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Table of Contents

Chapter 2

Specifications:

1)Gripper Challenge and Task ..................................................................................................................................

Gripper Challenges ......................................................................................................................... ……...

Gripper Tasks ....................................................................................................................................................

2)Pneumatically-driven highly under actuated 10-DOF robotic hand ..............................................................

Materials .......................................................................................................................................................... Silicon rubber (KE 550) .................................................................................................................................

Alumina ceramics 99 .....................................................................................................................

Alternative ……………………………………………………………………………………………………………..

Three Kinds of Grippers:

1)HEAVY DUTY ANGULAR PNEUMATIC GRIPPER

General Descriptions………………………………………………………………………………………………………………………………………….

Mechanism ...............................................................................................................................................................

Components and its working ...................................................................................................................................

Materials ..................................................................................................................................................................

Stainless Steel ............................................................................................................................................................

Hard Coated Aluminum ............................................................................................................................. Chromium Coating ....................................................................................................................................

2)Narrow Body pneumatic parallel gripper

General Descriptions………………………………………………………………………………………………………………………………………….

Mechanism ...............................................................................................................................................................

Components and its working ................................................................................................................................... Materials ..................................................................................................................................................................

Realistic Constraints:

Reliability……………………………………………………………………………………………………………………………..............

Economic Factor……………………………………………………………………………………………………………………………..

Safety…………………………………………………………………………………………………………………………………………….. Aesthetics…………………………………………………………………………………………………………………………............. Social Factors………………………………………………………………………………………………………………………………

Ethics……………………………………………………………………………………………………………………………………………. Security……………………………………………………………………………………………………………………………………….. Code and Standards…………………………………………………………………………………………………………

I. Specifications:

To determine the important specifications of the gripper, first it is fundamental to know the tasks and challenges that grippers would be responsible to do. Then, the selection of materials, the shape, and mechanism of the grippers should be logical and easy. After covering the descriptions of the materials, properties and mechanism, the fundamental specifications of the grippers should be covered.

1) Tasks:

A. Construction in building: 1) holding tools 2) squeezing and pressing on some bottoms and stuffs (light and heavy stuffs) 3) Knocking by hammer.

B. Fixing electrical wires in the street: 1) holding the wires 2) cut and joint wires.

C. In the factory: 1) Loading and unloading stuffs 2) Repair some machines 3) Products coverage. 4) Lubrication.

D. heating up some materials in furnace: 1) heating up some materials.

E. Aquarius Reef Base: 1) hurricane activity 2) locate the gripper on the work field part.

F. Grippers are used in robotics & electric gripping: for gripping assembly, tending of machines, lab automation & mobile robots.

2) Challenges :

High temperature, high location, hard places to reach because they are stuck, or narrow (need a lot of motion and advantages), aquatic location, electrical dangers (electric resistance), weather challenges, heavy stuffs, and m, and fast respond for functions. Beside these challenges, the grippers should work at extremely high and low gripping power, gripping without any damage, compressed air problem in vacuum grippers, small amount of oil decreases gripping power drastically, and slow motion.

II. Three Types of Gripper:

1) Pneumatically-driven highly under actuated 10-DOF robotic hand a)

A. General Descriptions:

Pneumatically-driven highly under actuated 10-DOF robotic hand (SARAH-Hand) is one of the best kinds of grippers that can be used in many work fields. In fact, the first point to pay attention about is the weight and density of the tool in the building construction. The most fundamental properties are presented for that point are the strength, pressure (force and area), hardness, and wearing and corrosion resistances. SARAH Hand has a good compact surface.

Due to necessities of flexibility and capability of doing any complex function, this gripper has 10 DOF. Also, its spherical compact surface is provided with rotational mechanism that let the fingers change their position so that it can be flexible to do complex repair or function. In fact, it is possible to move or rotate one finger and keep the others at stationary condition.

The purpose of using three fingers is to improve the controlling mechanism on the tools that are used for complex functions. For example, when using drill, two figures would be used for grasping the drill, and the third one is for turning on/off the drill. There are very few safety issues regarding the design and potential use of the gripper, the use of parts which should not cause any threats to humans.

B. Mechanism and Motor:

The mechanism of the SARAH-Hand uses the principle of a hand featuring under actuation among the fingers of the user. As one moves the fingers, the gripper is controlled by only one motor. A single motor is necessary for the operation of this type of motor because as the fingers move, or even a single finger, the gripper will independently grasp an object as firmly as possible. If a single finger closes and is firmly wraped around the object, the other fingers move to the point that they are all firmly closed. Actuation among the different fingers is achieved through an innovative gear differential mechanism. The differential is a train gear with three shafts, which gives it the ability to achieve an angular velocity for one shaft that has the average angular velocity of the other two shafts. Using a second motor in the griper will allow the orientation of fingers and enhance ability to achieve a spherical, cylindrical, and planar grasps.

c) Material

Silicon rubber (KE 550), stainless steel, and alumina ceramics 99.

Stainless Steel (gears, nails)

Alumina ceramics 99.5(limbs, wrist, joints)

Silicon

Rubber (KE 550)

(a)

Figure 1: Pneumatically-driven highly under actuated 10-DOF robotic hand (SARAH hand)

C. Materials Selection:

c-1: Silicon rubber (KE 550)

The first material is used for the grippers is the silicon rubber will be on the fingers’ thump Using the silicon rubber for the fingers’ thump is to grasp the tools, because it is not rough and can protect the tools from any future damages and the ceramics would be used due its sustaining capability and strength.

The silicon rubber can set in 150 C with no losing for any of its properties. Also, it can resist the coldness between -60 and -70 C. Since the thermal conductivity of silicon rubber is low (0.2 W/mΩ-K) and the thermal conductivity of alumina 99.5 is high (30.7 W/mΩ-K), the tool would be gripped by the rubber not ceramics. Due to their good heat resistance, they can work in high temperature locations. However, the silicon rubber cannot work on the furnace because it sometimes reaches to 1700-1760 C. So, ceramics can only can work at this high temperature.

Silicon rubber and ceramics have a good electric resistance. In fact, silicon rubber have a high electric insulation between 1 and 100 TΩ-m and its electric conductivity is among 0.01 and 10 Ω-m. So, when using the grippers in electric fieldworks, there are less chance of damage of the gripper.

In the Aquarius Reef Base and lubricating process in factories, the grippers can be efficient there and not exposed for damage. In fact, the silicon rubber can work underwater with only 1% of water absorption. Also, this rubber has a good steam and moisture resistance and oil, solvents, and other chemicals resistance. Figures 3-4 explain the resistance of steam and chemicals.

Figure 2: Silicon rubber Graphs

Figure 3: Silicon rubber Graphs (SP Value)

c-2: Alumina ceramics 99

The second material used for the grippers is the alumina ceramics 99.5 will cover the hard-side part because this alumina is commonly applicable on machine tools. The usage of this metal for the hard parts namely, limbs, wrist, and joints is because to its qualification because of its characteristics. The material has tensile strength, compressive strength, flexural strength, hardness, and elastic modulus (see figure 4). In fact, its hardness reach to 8 Kg/mm2. And, what justify its quality to be the hard part of the gripper its extreme Vickers hardness that reaches to 15.7 Gpa. Beside all these properties, this ceramic has a good stiffness and toughness level. In fact, its young modulus is 350 Gpa and the toughness is 3~4 Mpa(m2) . Also, the thickness of SARAH gripper reduces the potentiality of bending and damage, so the potentiality of damaging when holding heavy stuffs is less.

Other characteristics that make the material applicable in this type of gripper include its melting point and specific heat at 25C of alumina ceramics, which are 2050 C and 0.182 Cal/g/ oC. Secondly, its coefficient of thermal expansion at 251000 C is 8 X 10-6. Therefore, it is other than silicon rubber can be used in the furnace. On the other hand however, alumina 99.5 has a dielectric constant of 9.7 e' / eo, and it unfortunately has a high electric conductivity (30.6 Ω-m). Therefore, it can be only in contact with tools that has a good electric insulation.

c-3: Stainless Steel:

The main purposes of using stain steel in this gripper for nails, gears, or any other parts used is to assembly and connect each of the parts together. The stainless steel use in the grippers is mainly because they have a high resistance to corrosion. Secondly, the steel has high temperatures resistance and are also resistant to oxidation when exposed to air. Steel is commonly use in materials that may be exposed to hot temperatures. High chromium content in steel enables it to be resistant to corrosion and have the strength to resist high temperatures. In this context, this type of gripper may be used in areas where temperatures are elevated.

2) HEAVY DUTY ANGULAR PNEUMATIC GRIPPER:

A. General Description:

Some of the traits of heavy duty angular pneumatic grippers include spring assists on open and close options, high grip force to weight ratio, and hardened steel jaws. Additionally, the open and close options are available in different forces. The shape of the material the one needs to handle, shape of the parts, speed at which the parts are transferred, working pressure, and shape of the fingers determine the maximum load that grippers can handle.

The gripper has operating temperature of -20 to +180F [-28 to +82°C], and 0.2° Jaw backlash. The spring grip force is 3908N having Jaw displacement of 0.59in3.

Grip Force

80-3600 N

Stroke Spread

180 degrees

Weight

0.08-2.8 kg

Table 1:-Details of Two Jaw Style Toggle Lock Angular Gripper

the gripers can provide up to 180o angular travel, which allows the jaws to completely retract from the work area and eliminates the need for another gripper. The gripper body has two mounting surfaces, which has dowel pin holes that provides accurate mounting in different positions in case there is need to do complex repairs or provide different functioning abilities. It has property to detect magnetic material by adding HALL EFFECT PRINCIPAL (Shown in figure 5).

Figure 4: SERIES 5300 ANGULAR GRIPPERS

B. Mechanism:

In these types of grippers, the angular jaw travels an angle of total 180 degrees thus compelling the jaws of the grippers to retract back completely from the gripping which eliminates another required axis of travel. The Jaw rotations can be adjusted for a varied angle from -2 to 90 degrees which is associated with individual jaws and thus makes the gripper suitable for many industrial applications. Such type of grippers features in two jaw or three jaw design, both of which are fail safe toggle locking and is -2 degree past parallel.

C. Components their working and benefits:

In this type of grippers, the angular jaw of a gripper travels a total of 180 degrees, which compels the jaws of the grippers to retract back completely from the gripping and eliminates any need of another axis of travel. Each jaw can also be adjusted for a varied angle from -2 to 90 degrees making the gripper applicable in many industrial applications. The grippers sometimes feature in two jaw or three jaw designs, which are all fail safe toggle locking and -2 degree past parallel.

The following are the components and the working of the grippers’ parts:

1. The grippers have two styles of steel jaws capable of making an angular move of 180 degrees. The jaws enable the grippers to provide multiple mounting patters.

1. The bronze bearings attaching the jaws provide the jaws ability to resist wearing when they move to and fro. Additionally, the bearing enables rebuilding.

1. The jaws have neoprene seals to minimize contamination.

1. A long rod bearing helps the gripper get support and have an increased life because of the use of chrome plated steel piston rod.

1. Hall switches are available enabling position sensitivity. There is use of scientific techniques applied to detect magnetic fields and magnetic materials.

1. For the use of this gripper in narrow space oval piston is provided in the gripper providing high grip force in a narrow package.

1. The gripper also have both heavy and light force springs that can give the gripper an additional grip force without affecting the strength of the unit. It is connected with pressure tank and can operate within range of 65 to 150 psi.

1. The hard aluminum coating on the body with precision dowel holes provides the gripper with minimal seal wear.

1. Lastly, there is a solid state sensor transducer for jaw position sensing. The transducer is helpful since it receives command and implements on the jaws.

D. Materials:

- The gripper has different materials namely, stainless steel jaws, hard coated aluminum body, chrome plated steel piston, carbon, and heat treated steel dog.

Chrome plated steel piston rod

Carbon

Hardened precision pivot

for reduced wear

Heat treated steel dog

styles of steel jaws

ard coated

aluminum body

Hall Effect

Switches

Heavy and light force springs

Figure 5: SERIES 5300 ANGULAR GRIPPERS

d-1: Stainless Steel

The use of stainless steel is based on several considerations. One of the factors that make stainless steel essential in this type of gripper is the high resistance to corrosion even if exposed to air and water. Secondly, steel has very high melting point and can withstand high temperatures and its ability to withstand exposure to oxygen since it is hard to oxidize the material. High temperatures are needed to make oxygen react with steel. High composition of chromium element enables the material to be essential for use in case the gripper is to be exposed to high temperatures as its melting point is also elevated. In this context, the making of this type of gripper uses this element to make jaws that come into direct contact with heat and rusting elements.

Resistance to oxidation, or scaling, is dependent on the. Chromium content in the same way as the corrosion resistance. Most austenitic steels, can be used at temperatures up to 870°C.

Figure 6: Effect of Chromium content on scaling resistance of Chromium-Iron Alloy

Figure 6 indicates the approximate maximum temperatures in which the stainless still may still be used with high resistance to oxidation in dry air. The temperatures are dependent on the actual environment and in some instances, there may be destructive scaling, especially in substantially lower temperatures.

Another factor that make materials to be resistant to high temperatures is the creep strength, which refers to the ability of a material to resist destruction for a long time even when exposed to high temperatures. In regard to the stainless steel, it has good designs such as the Australian ASD120 Pressure Vessels and AS40141 Pressure Piping codes from the ASME and other bodies, which stipulate allowable working stress of each grade at different temperature ranges. In this perspective, it is the creep strength of the steel that enables this type of gripper.

Another factor that makes steel important for use in the making of the jaws is its stability. The problem associated with grain boundary carbide precipitation is a phenomenon where some steel may be exposed to higher temperatures of up to 815 degrees resulting in the reduction of corrosion resistance. Such properties relate to the intergranular corrosion and thus, there is need to use the material that evades such corrosion. In this context, the steel used in this type of gripper is capable. Another issue with steel that is not mixed with other elements is that exposure to high temperatures may lead to formation of sigma phase. Formation of the sigma phase in the austenitic steel used in this type of gripper is dependent on time and temperature.

The other factors that can be important in the use of steel in this type of grippers in high temperatures are carburization and sulphidation resistance. Sulfur has the ability to attack many alloys that are not stainless with nickel contents when exposed to high temperatures. At times, Grade 310 and Grase S30815, which have lower nickel content may be good but in other instances, totally nickel-free alloy is superior. When sulfur bearing gases are present under resucing conditions, it us better that pilot test specimen are run to determine the best alloy for this type of grippers.

d-2: Hard Coated Alumina

The light weight per unit volume of aluminum is desirable in many applications where its wear resistance prohibits- its use. Aluminum might also be desirable in some applications because of the ease of fabrication and its availability in a wide range of extruded sections. On the other hand, the weight or susceptibility to corrosion of case hardened steel make its use undesirable for the same applications.

0.002 inch hard coating will withstand an 1800°F Bunsen burner flame for one minute whereas the uncoated sheet blisters and warps considerably after 15 seconds.

The coefficient of thermal expansion of the hard anodic films differs considerably from that of the base metal. Checking will occur in the thicker films (0.002 inch and greater) when temperatures exceed 200 0F. However, the coating shows no tendency to spall, and the checking doe s not materially affect the corrosion resistance.

The hard coating is a nonconductor and acts as an insulator. Whereas standard anodize films break down at about 340 volts, the MHC coatings withstand a range of 500 to 3400 volts depending upon thickness. The breakdown voltage of a 0.003 inch Hard as film is reported as 20,000 volts.

The hard coatings show improved corrosion resistance over conventional anodizing. Little corrosion was shown by a 0.002 inch coating after 14 months continuous exposure to atmospheric and salt water corrosion. The coating is resistant to most of the common chemicals bat is attacked by strong acids and alkalis.

The coating itself is brittle and cracks easily but remains strongly bonded to the base metal. The coating process causes some loss of ductility in the tensile test of coated 0.060 inch.

d-3: Hard Chrome Steel

The hard chrome plating used in this type of gripper involves an electrolytic process that utilizes a chrome acid based electrolyte. To make the steel, steel is passed through a cathodes and passage of a DC current via lead anode. The material is ultra-hard with 850-100Hv (65-70Rc) and it is harder than most industrial abrasives and steel counter faces. The material have fives superb adhesion, which is greater than 10,000 psi. Before plating the steel, substrates are subjected to rigorous cleaning to free them from common contaminators. Chrome plating can be applied to a wide variety of substrates covering a wide range of engineering and high alloyed steels such as stainless steel and cast iron, lightweight aluminum alloys or titanium alloys, copper alloys, brasses and bronzes, and nickel-based alloys. The material or the hard chrome steel provides superb abrasion resistance even under very high contact stress. As a result, the hard chrome steel wear rate is very low even better than hardened steels or electro-less nickel.

3) Narrow Body pneumatic parallel gripper

A. General Description:

The narrow body pneumatic parallel gripper has the advantage of having a narrow design, 2-finger parallel gripper with smooth roller guides at the base of the jaws. With this trait, gripping and moving of small sized pieces as well as medium sized work pieces in low contaminated environments is easy. Such environments include assembly areas, testing areas, laboratories, and pharmaceutical industries. The base jaws are guided on double roller bearings enabling movement with minimum friction to the surfaces and smooth running. The grippers also has the benefits like synchronous jaw motion, With the narrow width, low profile, and long travel lengths, the grippers can be used for lighter objects. Other traits of this type of grippers include having manifold porting option, two jaw travels per bore size, and two sizes for each of the versions, that is, metric and imperial gripper versions The grippers have operating temperature of -20 to +180F [-28 to +82C], and within -0.002° in [-0.05 mm] of original centered position Jaw backlash. The total grip force is 124N having Jaw displacement of

0.28in3. The construction of the jaws of the grippers enables it to withstand high impact and shock loads.

Grip Force

40-180 N

Stroke Spread

10-31 mm

Weight

0.12-0.45 kg

Table 2: Details of Parallel Gripper

Figure 4: Narrow Body pneumatic parallel gripper

B. Mechanism

The mechanism of operation of the grippers is based on the characteristics of their jaws. The motion of the arms of the griper occurs along the direction of the piston shaft or the direction of the air cylinder. Gripper rods are then connected to the jaws of the gripper and are made up of rubber. There are two types of gripper jaws, which determine the gripping force of a gripper namely, friction grip and encompassing grip. Gripping rods are connected to the shaft of two pneumatic cylinders placed in opposite positions in relation to each other. The movement of the rods occurs during the intake and exhaust stroke whereby, the piston rods move out and in the pneumatic cylinder creating a motion of the rods across the pin joint. Such movement of the piston rods causes the gripper to grip or release objects as per the requirements of the user.

C. Components Working and Benefits

a. A synchronizer in gripper has function to control the speed and motion of jaws. The precision of the gripper is hardened and its life lengthened by the hardened steel synchronizer.

b. As describe above it has hall switches available for sensing position.

c. To work with this gripper in narrow places it has been provided with manifold porting, which allows for mounting on surfaces and created a narrow package with long jaw travel.

d. The gripper has hardened steel pins for minimal wear.

e. The angular gripper has chromium plate piston but it has anodized aluminum piston which extends lubrication life.

f. Aluminum body with precision machined jaw guides provides resistant jaw support because if rugged guides.

g. The hardened steel jaws also provide dowel holes for precise tooling location during a grip.

h. Stainless Steel jaws

i. Hard coated aluminum body

j. Anodized aluminum piston.

As they have the same material as above so its properties may be same.

Precision hardened steel synchronizer

Hardened

Steel Jaw

nodized aluminum piston

Hard Coated Alumunium Body

Hall

Effect

Switches

Figure 5: Narrow Body pneumatic parallel gripper

III. Realistic Constraints:

1) Reliability:

A. Angular Opening-Closing:

a) Three-finger grippers are used to let the work piece be centralized between the fingers, which are balanced by 120° .Furthermore, the three fingers slide the work piece to the center of the gripper to effortlessly hold the object. (Richards, Frances, 27-30)

b) The alternative options are angular and parallel grippers. The angular gripper is designed to hold a workpiece that have big sizes and odd shapes because its opening angles is radical; its full opening degree is 180 which work functionally when the vertical space is small. Also, there is a possibility to open to various number of angles, such as 30, 40, 80. Based on that, it also can grasp the workpieces with tight sizes same as parallel gripper. (31-39)

c) In general, these grippers have a various number of degrees of gripping forces that are approximately ranged among 20N to 6,500 N or more for high force models. The closing time is between 0.00l sec to 0.1 and sometimes it goes less than 0.001sec. The repetition accuracy come out with average of ± 0.01 to ± 0.05 mm. These engineering characteristics are very useful to provide an appropriate technique to control opening-closing motions.(40-49)

B. Strokes and Grasping:

Pneumatic grippers are typically designed as double actions — either air open or air closed. Variations include springs to ensure that the work piece remains gripped should air flow stop. Other options include long-stroke grippers with strokes from 20 to 150 mm.

C. Flexibility:

What's more, the use of flexible hands that can work with many different products will reduce the need for new featuring and tooling, which is required today to present parts to grippers in a certain orientation. Instead, hands can be configured to pick up different parts in any orientation. To do this, a typical gripping hand is built like a miniature robot, complete with seven servomotors (for seven DOF), a control unit for each motor, and several advanced sensors.

2) Economic Factors:

All three of the basic gripper styles are available in either pneumatic or electric versions. Pneumatic grippers are generally less expensive upfront, simpler, lighter, and offer higher gripping forces than electric versions, but electric grippers are somewhat less expensive to operate than their pneumatic counterparts. Even so, pneumatic systems offer diagnostic features that help maintenance personnel and machine operators identify air pressure loss, which contributes to higher energy costs in pneumatic systems. The material/frame in pneumatic grippers cost 50, 42 and 35$ respectively for above three grippers. The air pressure compression and tank cost about 90 $, and other miscellaneous parts are cost about 30$.

3) Safety and Gripping of Large and Small Parts:

A. Safety: The motion-design process starts with defining the shape and size of the work piece plus the available space, and then works up through the gripper and the rest of the mechanical assembly. For example, a lighter gripper requires a lighter handling system, while a heavier gripper requires heftier machine parts to support it. So there are very few safety constraints in lighter gripper but precaution should be needed during handling the gripper manually (Human handling).

B. Gripping:

As far as the gripper designs itself, this can vary substantially based on part size and shape. The smaller parts are more likely to be handled in higher volume, which requires fast-actuating designs for use in assembly as well as pick and place applications. Small parts generally refer to those weighing 5 lb or less. For larger parts (those that weigh 5 to 30 or 40 lb), grippers within the same product family can be up or downsized. Larger parts are generally found in material handling applications, such as moving parts on and off of conveyors or loading raw material into machine tools and removing finished parts.

4) Aesthetics:

The design of the above-mentioned Grippers are created in which the analysis of material and functioning is done so these grippers are optimized for function and simplicity for ease in 3D printing.

Therefore, it is easy to control the color and present the factors of the beauty in this project.

5) Social Factors:

A. Control System:

The control system provides a sequence, generally logical sequence for different robots which they are to follow up. The control system provides all the theoretical position values which are required for each step and thus continuously measures the actual positioning of the robot during each movement. When the robot functions, the control system quickly calculates the actual/theoretical/difference, along with other measured values and the stored data (such as theoretical speeds etc), and produces actuating variables which are required to drive the robot. (Dieterle ,Werner & Robert Bosch GmbH & Automotive Electronics & Driver Assistance Systems & Leonberg & Germany,275-276)

B. Automated Manufacturing and Advantages:

Automated manufacturing mainly symbolizes to the use of automation to reproduce things usually obtained in a factory. The automation technology has many advantages and thus it influence in the manufacturing and production processes.(275)

The main advantages of the automated manufacturing are higher consistency and quality, reduced lead times, simplification of production process, reduced man handling & improved work.

In field of Robotics and Automation, many research works have been done by many researchers. Some of the distinguished ones which are relevant and carries basic information for this paper have been highlighted briefly.

Ramesh Kolluru, Al Steward, Micheal J. Sonnier and Kimon P. Valavanis in their paper on ―A

Sensor based Robotic Gripper for Limp material handling ― proved that series of flat apparel grippers which are based on principle of pressure differential and suction can pick and place fabric materials reliably and with acute precision without causing any change to the structural dimensions of the fabric.

Junbo Song and Yoshihisa Ishida in their paper on ―A Robust Sliding mode Control for Pneumatic Servo Systems successfully simulated and applied the results of a robust sliding mode control scheme for pneumatic servo systems. It is proven that due to many of the uncertain bounds used in structural properties of pneumatic servo systems which are used in controllers design and also due to the insensitivity of the error dynamic to uncertain dynamics, the model is strong and a robust one.

As above scholar do a lot of work in gripper technology so best combinations of shape, size, weight, power, and power consumption are, the idea of a single, completely proven idea from which to build this project on is only based on the social constraints that stem from published items in literature.

f) Ethics:

The standard code of ethics which is directly applicable to the robot as gripper is a part of robot. Other important categories are less familiar, such as the potential for a robot operator to unknowingly command a robot to do something illegal and thereafter be held responsible for its actions. Issues such as wrongly attributing too much intelligence to a robot can be highly dangerous. So, the gripper have to follow the command what the robot given to it. In case of manually operating gripper a human should aware of illegal activities.

They cover the possible future capabilities of robotics, e.g. programming highly intelligent robots to make ethical decisions. They deal with the ethics of human-robot interaction, based on a level of robot intelligence which is currently unrealistic.

Even with these inconveniences, it is imperative that the objective remains the first priority before temporary convenience. This realization is important because it allows those attempting the project to work ethically and diligently while returning beneficial results.

With everything mentioned in mind, the engineers performing this design improvement have remained truthful through everything completed. This includes the covered topics, the project’s foundation, research involved, self-contributed ideas. The personally contributed ideas are based on previous experiments performed, proven theory, and concepts taught within class.

6) Security:

As gripper is the part of robot so a well care is needed to secure the parts of robot as well as gripper.

Once the gripper and robot dimensions and details are accuracy, all parts of the project could be save.

7) Code and Standards

We will be following the code and standards of ASME and OSHA, and they are as following:

· A normal convenience in everyday life functioning without incident.

· “Level playing field” for both manufacturers and users of the equipment or systems.

· Items manufactured uniformly, providing for interchangeability

· Tests and analyses conducted reliably, minimizing the uncertainty of the results

· Facilities designed and constructed for safe operation

· Observe testing that is done to find hazards in the workplace and get test results

· Training about hazards, methods to prevent harm, and the OSHA standards that apply to their workplace.

Pugh Chart:

- Based on the Pugh chart and data mentioned above, the gripper will be used in many fields, and it is important for jaws to be flexible and have many options of opening and closing angles. Therefore, the parallel gripper cannot be efficient for this project. And, the angular and three fingers grippers have a good ability to deal with objects with different shapes and dimensions.

Chapter 3

Background

Theory

The Human Hand………………………………………………………………………………………..

The Iron Hand of the Reichsritter Götz Gottfreid von Berlichingen………………………………..

The Shadow Hand………………………………………………………………………………………..

The Bh8-Series Barrett Hand…………………………………………………………………………..

The Dlr Hand ii…………………………………………………………………………………………..

Primarily Design

Pneumatically-driven highly under actuated 10-DOF robotic hand Grippers……….

Angular Grippers………………………………………………………………………………………………………….

Narrow Body pneumatic parallel gripper……………………………………………………………………… Chapter 3

Design Analysis

• Pneumatically-driven highly under actuated 10-DOF robotic hand

a) Dimensions………………………………………………………………………………

b) The Gripper Construction ……………………………………………………………..

c) Material Test…………………………………………………………………………….

d) FEM Analysis……………………………………………………………………………

e) Under load Behavior……………………………………………………………………

f) Table of Data……………………………………………………………………………………………………………

• HEAVY DUTY ANGULAR PNEUMATIC GRIPPER

a) Dimensions………………………………………………………………………………

b) FEM Analysis……………………………………………………………………………

c) Under load Behavior…………………………………………………………………….

• Calculation

a) Normal Gripping Force…………………………………………………………………

b) 3 ARM Robotic Gripper Torque Requirements………………………………………

c) Angular Gripper Torque Requirements……………………………………………….

· Matrix Decision:

I. Backgrounds:

In the chapter2 work we have do research basic analysis and specifications of grippers. Chapter 3 describes background about the above grippers. This chapter also describes the human hand, one historical artificial hand and three robotic graspers. First imitations of the human hand are coming from the prosthetic and in the last few years many robotic hands had be developed around institutes all over the world. This chapter shows and describes three different robotic graspers. One industrial robotic grasper (the Barrett hand), one humanoid robot hand without a wrist (The Shadow dexterous hand) and one humanoid robot hand including a wrist (The DLR Hand II).

II. Theories:

1) THE HUMAN HAND:

Developed under many years of evolution the human hand has made us to what we are today. The human hand is composed by 27 different bones and the opposing thumb is characteristic for the human. The opposing thumb enables the precision grasp between the long finger and the thump which enables us to write or to perform precision work. Further the hand has 20 DOF and the most muscles are placed in the forearm and transmit their developed force via tendons to the fingers. The bigger muscles in the hand are the thenar muscle on the thumb side and the Hypothenar muscle on the side of the little finger.

The Thenar muscle The Hypothenar muscle

2) THE IRON HAND OF THE REICHSRITTER GÖTZ GOTTFREID VON BERLICHINGEN

First imitations of human hands come from the prosthetic, as for example the iron fist of the Götz of Berlichingen (1480-1562). That hand had five separate fingers, which could be bent passively and could be redeemed by pushing a button. The hand had a mass of 1.5 kg what wasn’t too bad for that time.

The Iron Hand

3) THE SHADOW HAND

The Shadow Dextrous Hand is an advanced humanoid robot hand. The hand can perform 24 different grasps and is as close as it gets to a human hand. The hand has a total mass of 3.9 kg including all sensors and actuators. It’s built from a plenty different materials; the forearm bone is made of steel, the palm is made of acetyl, aluminum and polycarbonate and the fingers are made of acetyl. The hand is driven by 40 air muscles (40 degrees of actuation) which are mounted one the forearm. These are connected with tendons too the joints. The air muscle technology requires both electric current and compressed air. The hand is equipped with tactile sensors at the finger tips for feedback control. Each sensor has an output range from zero up to one kg.

THE SHADOW HAND

4) THE BH8-SERIES BARRETT HAND

This hand is a multifunctional industrial grasper for objects of different shape. The hand has four controlled degrees of freedom and is able to perform precision and power grasps. It has three fingers and two of them are spreadable, each finger has two joints and 1 motor and all together the hand has four DOA and eight DOF. These motors are Samarium-Cobalt, brushless, DC, servo motors and the Barret hand can grasp up to 6 kg at an own mass of 1.18 kg. The hand is controlled by optical incremental encoders and joint torque sensors.

5) THE DLR HAND II

This Hand is a further development of the DLR I Hand. In this further developed version the focus was to improve autonomous grasping. The fine manipulation possibilities where reached by using fully integrated actuators and electronics. The DLR Hands are as the hand in the KTH Mechatronic Lab just hands without a forearm. Hands with an integrated forearm open up for much better design opportunities (anthropomorphic design) because the additional space in the forearm can be used for placing actuators and electronic components. One disadvantage of hands with integrated forearms is that they can’t be placed on robot arms.

The DLR II hand has an open skeleton design which enables better maintenance and also the testing of different grasp surfaces without redesigning finger parts. When power grasps are performed it is important that all fingers are parallel but when precision grasps are performed it is necessary to have large regions of intersection of the ranges of motion. Furthermore, it is important that the thumb and the ring finger are placed opposite to each other. To perform these different assignments the hand has 16 DOF and 12 DOA. The actuators are placed in each finger joint. The base joint requires a bevel gear which is directly coupled to the motors to enable the two DOF. The hand is equipped with sensors for torque, position, and speed and temperature control. The control of the fingers and the hand is done by an external computer.

III. Primarily Design:

The task was to design a robot gripper. The focus of this thesis within the project lied on to improve the shape, function and assembly properties of the robotic gripper. In addition, we have to discuss the skills and the modern tools required to complete the design. To design the gripper

Auto CAD and Solid works software was used. FEM analyses where done in Pro Mechanical.

In this project, there are three selections are shown below:

1) Pneumatically-driven highly under actuated 10-DOF robotic hand

a) Design

The gripper is made in a lightweight construction and contains of different parts. Besides these parts there are some other parts needed to put the parts together, a spring to unbend the arms of gripper, three screw plates and three screws to fasten the spring and to keep the arm together.

Three Arm CAD model Side view of ARM

3D front View of ARM Base of gripper

Rendering of CAD Design

b) Design Analysis:

b-1: DIMENSION

The Gripper has three ARMs. The dimension and description of the arms, base, and handle is given below.

Side view of ARM

Base of gripper Green base of Finger

Whole Finger

b-2: THE Gripper CONSTRUCTION

The Hand has two fingers and one thumb. To keep the construction light, these are hold together by an aluminum palm. The gripper Arms and all actuators and sensors are fastened with screws on the palm. The gripper is like two finger and with one thumb, the thumb is placed opposite and in the middle of the two fingers. This position was taken because it enables a nearly humanlike movement and it keeps the torques small.

b-3: Material Test

The existing hand is built in three different materials; alumina ceramics, rubber, and steel. The possibility to build the whole hand in alumina was tempting. This would enable to manufacture the whole hand in Rapid Prototyping and that opens up for a very free design. At first, the shape of the hand wouldn’t be limited by the manufacturing method. Second the finger base could be integrated into the hand. Third, actuators, motors, and cables can be fastened directly in the palm (hand) and fourth, all parts would be manufactured to one price.

b-4: FEM Analysis

By doing FEM analyses on the existing CAD files. The tensile strength of the material is 42

MPa and the FEM analyses showed that the stress didn’t reach this level even at the critical point at the finger base. The stress was 20 KPa.

b-5: Under load Behavior

FEM analyses of the thumb base and the hand backside where done to get a better understanding of their behavior under load .The conditions for the hand backside were that it was locked at the interface to the robot arm and a load off 1, 5 kg was applied at the outermost edge of the two finger bases. In two figures the most sensitive locations for deformation and stress are illustrated. The thumb base was locked around the fastener for the thumb axis and a force of 30 N was applied to the most distal surface of the thumb base. Also here the most sensitive locations for stress and deformation are illustrated. It also becomes clear that the yield stresses under the applied loads by far don’t reach the tensile strength of the used material (42.3 Mpa).

b-6: Table of Data:

Resultant Load on Model:

in global X direction: 1.488329e-08

in global Y direction: 9.217988e-10

in global Z direction: 3.000000e+04

Measures:

Name Value Convergence

-------------- ------------- -----------

max_beam_bending: 0.000000e+00 0.0%

max_beam_tensile: 0.000000e+00 0.0%

max_beam_torsion: 0.000000e+00 0.0%

max_beam_total: 0.000000e+00 0.0%

max_disp_mag: 3.412082e+07 2.4%

max_disp_x: 1.352688e+07 2.1%

max_disp_y: -3.289546e+06 8.6%

max_disp_z: 3.194036e+07 2.4%

max_prin_mag: 4.446599e+04 17.5%

max_rot_mag: 0.000000e+00 0.0%

max_rot_x: 0.000000e+00 0.0%

max_rot_y: 0.000000e+00 0.0%

max_rot_z: 0.000000e+00 0.0%

max_stress_prin: 4.446599e+04 17.5%

max_stress_vm: 3.891670e+04 17.6%

max_stress_xx: 4.167295e+04 16.1%

max_stress_xy: -6.295829e+03 1.6%

max_stress_xz: 1.402057e+04 2.6%

max_stress_yy: 1.495838e+04 20.3%

max_stress_yz: 5.094920e+03 11.0%

max_stress_zz: 2.357535e+04 31.1%

min_stress_prin: -1.959093e+04 5.7%

strain_energy: 3.113082e+11 2.5%

b-7: Calculation:

When gripping with frictional force, calculate the necessary gripping force as shown below.

b-7-1: Normal Gripping Force :

(1) F: Gripping force [N]

(2) μ : Coefficient of static friction between the finger attachment and the work part

(3) m : Work part weight [Kg]

(4) g : Gravitational acceleration [= 9.8m/s2]

(5) Jaw factor for a Friction grip is assumed as=4 (Rule of Thumb)

(6) Jaw facto for Encompassing Grip=1 (Rule of Thumb)

A condition in which a work part does not drop when the work part is gripped statistically:

· Fμ > W

· F > mg/μ Necessary gripping force as the recommended safety factor of 2 in normal transportation:

· F > mg/ μ x 2 (safety factor)

· When the friction coefficient μ is between 0.1 and 0.2:

· F > mg/ μ x 2 = (10~20) x mg 0.1~0.2

· F = 1.5kg * 9.8/0.2 * 2

· F = 36.75

*As the Coefficient of static friction increases, the work part weight also increases.

b-7-2: Force required to Grip= Part weight (1+Part Gr) * Jaw style Factor

· Friction grip= 1.5*10(1+1.5) *4= 150 N * Part Weight = 1.5 (Suppose)

b-7-3: 3 ARM Robotic Gripper Torque Requirements

The torque in a gripper is generated by two sources generally:-

· Torque developed by the gripper arms on itself

· Torque developed by the acceleration & weight of the part

GRIPPER TORQUE=gripper Force*Length of the jaw (It is the distance from the gripper face)

Jaw length= 149.7695mm=0.1497695m

· Jaw Torque (friction grip) = 150*0.149765= 22.46475 N-m

Torque generated by acceleration & weight of the part:-

· Part torque= Jaw length*Part Weight*(Acceleration+1 G if up & down)

· =1.5*10*0.1497695 m

· = 2.2465 N-m

Grand total of all Torques on the Gripper:-

· The Total torque that is developed on the gripper is the sum of the torque developed on the jaw and the Torque developed on the part.

· Total Torque= Jaw Torque + Part Torque

Total torque=22.46475 + 2.2465 = 24.71129 N-m.

c) THE SERVO (For 3 Jaw gripper) :( Abdullah)

To perform the rotary movement of the thumb a servo from bluebird technologies is used in the old hand. A Servo has a very strong torque at low dimensions and is suitable to realize the rotary movement. So it was decided that even the servo shall stay the same in the new hand.

Three air cylinders and the servo are placed in the palm and the third is rotating with the thumb. All air cylinders are placed in the hand and the servo is placed behind the thumb. Using this solution the thumb would become too far away from the fingers. The servo is placed behind the thumb joint and the motor is placed in front of it. This concept allows it to adjust the thumb base in the shown shape closer to the fingers. The concept used in the final design will be described closer in the chapter redesigning the thumb joint.

The Thumb

base with servo placed behind and the motor in front.

The thumb base

The angular form of the thumb makes it possible to move the bearing of the thumb more backwards in the hand. The angel between the base foot and the base top is 120 degrees. Simultaneously the thumb base comes five millimeters closer to the two finger bases. The tendon which comes from the distal part of the thumb runs at the inside of the thumb base and leaves the thumb right in the rotation axis of the thumb. The air cylinders are placed behind the thumb base to roll up the tendon.

The servo which performs the rotation of 90 degrees lies in front of the thumb joint.

The thumb base in three different views

2) HEAVY DUTY ANGULAR PNEUMATIC GRIPPER

a) Design

The gripper is made in a lightweight construction and contains of different parts. Besides these parts there are some other parts needed to put the parts together, a spring to produce stretching force between the arms of gripper, two screw plates and two screws to fasten the spring and to keep the arm together.

Pin Jaw Opened

Jaw Jaw Closed

Body Sketched Body Diagram

Adjustment Bock Sensor Block

b) Design Analysis:

b-1: Dimension

The gripper has two arms, outer body, spring, sensor block etc and their dimention is given below together.

Dimensions of the angular gripper

b-2: FEM Analysis

By doing FEM analyses on the existing CAD files. The tensile strength of the material is 50 lbs. [222 N, 89 N]. For static and dynamic, it is respectively about 20 1bs.

b-3:Under load Behavior

FEM analyses of the angular gripper done to get a better understanding of their behavior under load. The robot arm and a load off 1, 5 kg was applied at the outermost edge of the two finger.

It also becomes clear that the yield stresses under the applied loads by far don’t reach the tensile strength of the used material (50 lbs).

FEM analysis of angular Jaw gripper

b-4: Calculation: Angular Gripper Torque Requirements :

GRIPPER TORQUE=gripper Force*Length of the jaw (It is the distance from the gripper face)

· Jaw Torque (friction grip) = 150*0.0311150= 4.66725 N-m

· * Jaw length= 31.1150mm=0.031115m

Torque generated by acceleration & weight of the part:-

· Part torque=Acceleration(Gr)* jaw length

· =1.5*10 * 0.031115 m

· = 0.466725 N-m

Grand total of all Torques on the Gripper:-

· The Total torque that is developed on the gripper is the sum of the torque developed on the jaw and the Torque developed on the part.

· Total Torque= Jaw length* Gripper Force+ Jaw length*Part Weight*(Acceleration+1 G if up & down)

· Total torque=4.66725 + 0.466725 = 5.133975 N-m

The Total torque that is developed on the gripper is the sum of the torque developed on the jaw and the Torque developed on the part.

IV. Matrix Decision

		ALTERNATIVES
Model	Three Fingers	Angular
Criterion	Weight	Rating	Score	Rating	Score
Maintainability	3	2	6	3	9
Relibility	5	4	20	2	10
Weight	3	3	9	4	12
Envoirmental Resistance	5	4	20	3	15
Cost	1	3	3	4	4
Safety	4	2	2	3	12
Flexibility	5	4	20	3	15
Human hand simulation	5	4	20	1	5
Ease of Use	3	2	6	3	9
Aethetics	1	4	4	2	2
Soft Gripping Force/torsion	4	4	16	3	12
Motion/ speed	3	4	12	1	3
Dimensions	4	4	16	2	8
Total	46	44	154	34	116

The reliability of three fingers has 120 degree offset, while angular gripper has 30, 40, or 80 degrees. In fact, the field of work sometimes requires having a gripper capable to hold up some unshaped and big stuffs. These stuffs widely need a gripper have more than 100 degree of freedom. Therefore, the angular gripper is not sufficiently wide to hold up these stuffs same as three finger grippers.

The weight of the gripper should trend to be small. In fact, if the gripper has a big size, it will so hard to do fast functions. Also, the arm should tend to have so strong materials with high cost. The weight of the angular gripper is about 1.5*9.8= 14.7N, while three finger’s gripper weight is 2.8kg*9.8. For, weight

Materials:

Cost:

Safety: Since the gripper is assembly complex, it tends to be less safe than sample gripper. In fact, the angular jaws components are very sample. It only needs a piston to control the jaw and one servo-motor to rotate the gripper. Also, the maintenance for this gripper is basic, while humans’ exposing to risks is higher when using three fingers grippers. It is very complex (multiple of differential gears and pneumatic pistons). Also, the repairing is so advanced and need and expert because this gripper is responsible for a multiple of motions. The probability of exposing to damage is more in three finger dues to it complex mechanism.

Flexibility: 10 DOF,

As it is clear the three fingers is more complex and similar for human hands. The angular gripper jaws are not flexible as human hand. Also, the principle details of human’s hands that help them do complex functions are not provided with angular jaws. Otherwise, three fingers gripper has many specific details that are simulated with humans’ hands. For example, the compact surface is doing the same function of human’s Plame. Also, the surrounding area of rotation compact sound same as the wrist. Finally, every finger in this gripper consist of three levels exactly same as humans.

Chapter 4

c) Pneumatically-driven highly under actuated 10-DOF robotic hand

One of the most complex parts of our motor-driven highly underactuated robotic hands is the gear differential mechanism that provides the under actuation between the three fingers. A much simpler substitute of this differential could be used in the case of pneumatic or hydraulic actuation — just a distributer with one input and three outputs. While, in many applications, pneumatic or hydraulic actuation is not suitable, in many other, this type of actuation is standard. The robotic hand is the smallest of all our underactuated hands. As described above, the differential was replaced by a multiple distributer. Three pneumatic cylinders are used for closing the fingers in combination with three flow control valves. The valves are currently manually adjusted to set the speed of closing the fingers. The force of the fingers can be controlled by the air pressure of the first air supply. A push button is used to let the air flow that closes the fingers. Two other pneumatic cylinders are used for orienting the fingers. The hand can have three discrete configurations — for cylindrical grasping, for spherical grasping, and for parallel two-finger grasping. A three-position switch is used to direct the flow to one of the cylinders or to disrupt it, thus selecting one of the three configurations. The result is a relatively low-cost multi-functional self-adaptive robotic hand that fits directly onto any industrial robot that can use pneumatic grippers

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