How To Calculate The Linear Displacement Per Encoder Count; Notes On Max Velocity And Acceleration/Deceleration Profile - THORLABS Z8 Series User Manual

Z8 Series DC Motor Actuator

5.2 How to Calculate the Linear Displacement per Encoder Count

For the Z806, there are 512 encoder counts per revolution of the motor. The output
shaft of the motor goes into a 67:1 planetary gear head. This requires the motor to
rotate 67 times to rotate the 1.0 mm pitch lead screw one revolution. The end result
is the lead screw advances by 1.0 mm.
To calculate the linear displacement of the actuator per encoder count:
512 x 67 = 34,304 encoder counts per revolution of the lead screw
Linear displacement of the lead screw per encoder count is:
1.0 mm / 34,304 counts = 2.9 x 10-5 mm (29 nm)

5.3 Notes on Max Velocity and Acceleration/Deceleration Profile

Although the max velocity is quoted at 2.6 mm/sec, it is possible to drive the Z8 motor
at speeds in excess of this figure. However, at higher velocities the controlled
acceleration and deceleration profiles may be affected. If these controlled profiles
are required, then the speed should be reduced to around 2.3 mm/s maximum.
Furthermore, the velocity ripple due to the PID loop in the KDC101 driver is greater
when the unit is running at the higher velocities.
Velocity
(mm/sec)
Velocity
(mm/sec)
Fig. 5.1 Effects of Higher Velocity on Acceleration/Deceleration Profile
Page 8
Graph A - max velocity <2.3 mm/sec
2.3
Graph B - max velocity >2.3 mm/sec
velocity ripple due to PID loop
2.6
controlled profile
P1
rapid deceleration to set point
P1