Research Project of intelligent CAD model :Electric Linear Actuator

Introduction to Linear Actuators: Precision Linear Motion Accomplished Easily and Economically

Part 2 of 2

In Part 1, we discussed the basics of a stepper motor-based linear actuator, one of the

most effective ways to convert rotary into linear motion for a wide range of applications. In Part

2, we will explain how to accurately size a linear actuator.

How Is a Linear Actuator Sized?

Sizing a linear actuator is quite easy once you understand the basic needs of the

application. The following is the minimum information needed to begin sizing the proper

device.

1. Linear force needed to move the load, expressed in Newtons (N)

2. Linear distance the load needs to be moved, expressed in meters (M)

3. Time required to move the load, expressed in seconds (s)

4. Table 1 – illustrated below

5. Performance curves illustrated in Haydon linear actuator catalogs

Power Requirements

The power required to meet the application is now calculated using the parameters above.

This will allow the user to easily choose the correct motor framesize needed.

P linear = (distance traveled in Meters) (force in Newtons) (Time to travel the distance in Seconds) = watts

Once the power is known in watts, choose the proper frame size of the actuator as listed in Table

1. All stepper motor linear actuators require a drive to send the pulses to the motor. As seen in

Table 1, the power for both an L/R drive and a chopper drive is listed. Most applications today

use an electronic chopper drive. Unless the application is battery-powered (as in a handheld

portable device), a chopper drive is highly recommended to get maximum performance from the

linear actuator.

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Table 1. Frame Sizes and Performance Based On Required Output Power

Hybrid Single Stack

Max. Linear Power (watts)

Series Size Max Force (N)

Linear Travel Per Step (micron) L/R Drive Chopper Drive

21000 8 45 1.5 – 40 0.3 0.37

28000 11 90 3 – 50 0.27 0.51

35000 14 220 1.5 – 50 0 .59 1.5

43000 17 220 1.5 – 50 1.02 2.31

57000 23 880 4 – 50 1.47 6

87000 34 2200 12.7 – 127 N/A 21.19

Hybrid Double Stack

Max. Linear Power (watts)

Series Size Max Force (N)

Linear Travel Per Step (micron) L/R Drive Chopper Drive

28000 11 133 3 – 50 N/A 1.14

35000 14 220 15.8 – 127 N/A 2.7

43000 17 350 15.8 – 127 N/A 4.62

57000 23 880 12.7 – 127 N/A 10.08

Canstack

Max. Linear Power (watts)

Series Size Max Force (N)

Linear Travel Per Step (micron) L/R Drive Chopper Drive

15000 15mm 7 20 0.025 0.03

20000 20mm 16 25 – 100 0.05 0.06

Z20000 20mm 35 25 – 100 0.09 0.23

26000 26mm 50 6 – 100 0.17 0.18

Z26000 26mm 80 6 – 100 0.18 0.48

36000 36mm 160 3 – 100 0.23 0.69

46000 46mm 260 12.7 – 400 0.55 1.13

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Velocity

After calculating the mechanical power needed to meet the application requirements, the

linear velocity in inches per second is calculated using the following equation:

Velocity linear = required travel distance (in) Time to achieve travel (s) = in / s Force vs. Linear Velocity Curves

Once the required actuator frame size is determined and the linear velocity is calculated,

the “force vs. linear velocity curve” is used to determine the proper resolution of the actuator

lead screw.

Figure 1. Size 17 Actuator - Force vs. Linear Velocity Chart

Actuator Life

There are many variables that ultimately determine life of the actuator. The best way to

predict life is through application testing, which is highly recommended. There is, however, a

first approximation technique that can help estimate this value. The stepper-motor prime mover

contains no brushes to wear out and also utilizes precision, long-life ball bearings. The main

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wear component is the power nut. The number of cycles can be summarized as a function of

load, as illustrated in Figure 2 below.

Figure 2. Cycles on a Standard Stroke Actuator as a Function of % Max Load

Example #1

Application Requirements:

Req’d Force (lbs) = 15 lbs

Req’d Travel (in) = 3 in

Time To Achieve Travel (s) = 6s

Desired Cycles = 1,000,000

Linear Velocity (in/s) = 3 in / 6 s = 0.5 in/s

• COMPUTATION: Calculate the initial rated force based on required # of cycles:

Step 1:

Refer to Figure 2 and determine the correct sizing factor needed in order for the actuator

to achieve the required 1,000,000 cycles. This is illustrated with the blue line in Figure 3 below.

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Figure 3. Safety Factor Needed To Meet 1,000,000 Cycles

Step 2:

As indicated in the chart, in order to get 1,000,000 cycles, a factor of 0.5 must be used

when sizing the actuator. The initial rated force required in order to meet the load after

1,000,000 cycles is therefore…

15 lbs / 0.5 = 30 lbs

Step 3:

Convert lbs to Newtons (N)

30 lbs / (0.225 lbs / N) = 133 N

• COMPUTATION: Determine required travel in meters

3 in x (0.0254 M / in) = 0.0762 M

• COMPUTATION: Choose the proper frame size actuator using the selector chart

Step 1:

Determine the required linear mechanical power in watts

P linear = (133N x 0.0762M) / 6s = 1.7 N-M / s = 1.7 watts Step 2:

Use Table 1 to determine the correct frame size actuator. As discussed earlier in the

aticle, most applications will use a chopper drive to supply the required input pulses to the

stepper motor. The 43000 (Size 17 Hybrid) was chosen for this application, as highlighted in the

“Hybrid Single Stack” section of Table 1.

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Hybrid Single Stack

Max. Power; watts

Series Size Max Force (N) Linear Travel / Step (micron) L/R Chopper

21000 8 45 1.5 – 40 0.3 0.37

28000 11 90 3 – 50 0.27 0.51

35000 14 220 1.5 – 50 0 .59 1.5

43000 17 220 1.5 – 50 1.02 2.31

57000 23 880 4 – 50 1.47 6

87000 34 2200 12.7 – 127 N/A 21.19

• COMPUTATION: Determine the proper resolution using the “Force vs Linear Velocity”

chart

As determined by the life calculation performed above, an initial load of 30 lbs is to be

moved at a velocity of 0.5in/s. The resulting lead screw resolution required in the Size 17 hybrid

motor is 0.00048” (J resolution), as indicated in Figure 4 below.

Figure 4. Lead screw resolution required in the Size 17 hybrid motor is 0.00048” (J

resolution), as indicated.

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COMPUTATION: Verify selection by checking force at the required step rate

Earlier in the paper, it was discussed that the lead screw advances based on the number of

input steps to the motor. Haydon performance curves are expressed in both “in/sec” (as

illustrated in Figure 4) and also in “steps/sec” (Figure 5). As an effective check, verify the

selection by checking the force at the required step rate.

Resolution chosen 0.00048 in/step (“J” screw)

Req’d linear velocity 0.5 in/s

Req’d step rate (0.5 in/s) / (0.00048 in/step) = 1041 steps/s

Figure 5.

Figures 4 and 5 are good illustrations of how the pulses to the stepper motor translate into

linear motion through the lead screw.

Conclusion

Through the use of stepper motor-based linear actuators, rotary-to-linear motion takes

place inside the motor itself. This method offers unique advantages over alternative approaches,

such as fewer components, smaller overall footprint size, high force output, and long stroke

lengths. What’s more, the high precision, repeatability, long component are especially attractive,

as are the high resolutions possible.

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In addition, the use of the stepper motor translates to a lower overall cost for OEM

equipment builders in terms of development and production. Most importantly, this method can

be utilized in a variety of vertical markets, including medical, laboratory instrumentation,

semiconductor, aerospace, and virtually any other application where precision linear motion is

required.

About HaydonKerk Motion Solutions

HaydonKerk Motion Solutions is the joining of two world class brands in the field of

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linear actuators, rotary motors, lead screw assemblies, and linear rail and guide systems used in

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http://www.HaydonKerk.com.

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