Haydon Kerk basic product training 2009.

• Why a stepper motor / actuator?
• Unlike other motors, stepper are unique, as
they move a given amount of rotary motion
for every input pulse.
• Can-stack motors will step 7.5 or 15
rotational degrees for each input pulse.
• Hybrid motors will step 0.9 or 1.8 rotational
degrees for each input pulse.
• This allows the motor to be used very
effectively for positioning applications.

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Types of linear actuators

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Catalog review:

• Force vs Linear velocity
• Force vs Full Steps / Second

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• Actuator life

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percent load vs number of cycles

120
100
percent %

80
percent load vs
60
number of cycles
40
20
0
1 100 10000 1000000 1E+08

number of cycles

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• Sizing the actuator

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How to size a linear actuator:
• The following information must be known:
• The load to be moved. ( Expressed in
Newtons )
• The distance that the load is to moved. (
Expressed in Meters )
• The time required to move the load the given
distance. ( Expressed in seconds. )
• The mechanical power is then calculated in
watts.
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Linear power: P lin ( watts ) :

P lin = (distance traveled in Meters) ( force in Newtons )
Time to travel the distance in Second = watts

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• Example:
• Let us assume that we have the
following application needs:
– force = 15 lbs
– travel = 3 inches
– time to achieve the travel = 6 seconds
– number of desired cycles = 1,000,000
– linear velocity = 3 inches / 6 sec. = 0.5
inches per second

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• Calculate the initial force based on number of cycles desired
– From the percent load vs number of cycle table determine the %
loss after the 1,000,000 cycles.
– This = 50%; Therefore the initial force required = 15 lbs / .5 = = 30
lbs.
– Convert this to Newtons. 30 / 0.225 = 133 Newtons

Life expectancy

120
100
percent %

80
percent load vs
60
number of cycles
40
20
0
1 100 10,000 1,000,000 100,000,000

number of cycles Sold & Serviced By:

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Example continued:
• Verify your selection by checking force at
required step rate.
• The resolution we chose is “J”. (0.00048
inches per step)
• Linear velocity = 0.5 inches per second
• Step rate = 0.5 / 0.00048 = 1041 steps per
second
• Verify that the required force is present at
1041 steps per second using the force vs
step rate curve.

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• Ramping:
• Sometimes, we may need to have the actuator
perform a bit faster than that shown in the catalog
curves.
• To do this we apply ramping to our input pulses.
• This means that we start slowly but RAMP the pulse
rate to a high final velocity.
• This final velocity is higher that then velocity the
actuator could reach without ramping ( acceleration )

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Ramping continued:
• Ramping can typically result in an increase step rate
of approximately 60 %.

force vs linear velocity

400 Z = 1.6 x Z

300
no ramping
lb s

200
with ramping
100

0
0 1 2 3
inches per second
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• Resolution, Accuracy, &
Repeatability…
• What’s the difference??

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• RESOLUTION:
• The incremental distance the actuator’s output shaft will extend
per input pulse (mm/step)
• Formula: _______LEAD_________
(360 degrees / step angle)

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• ACCURACY:
• The difference between the theoretical distance and the actual
distance traveled is the actuator’s accuracy.
• Example: For an actuator utilizing a screw with a 1” lead, 360
deg of rotary motion will result in a theoretical 1” stroke. Due
to manufacturing tolerances in the components of the actuator,
the actual travel will be slightly different. The magnitude of this
difference is the accuracy of the actuator.

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• REPEATABILITY:
• The range of positions attained when the actuator is
commanded to approach the same target multiple
times under identical conditions.
• Example: Allow the actuator to extend a given
distance from it’s home position. Measure and
record this distance and call it “x”. Retract the
actuator back to it’s home position. Command the
actuator to return to the commanded distance “x”.
The difference between the new distance traveled
and the original distance “x” is repeatability.

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Haydon Kerk basic product training 2009.

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