Encoder Question

[scrambled]

Hi everyone--


I am planning on ordering my encoders from US Digital this week. I have a question about the CPR (Counts Per Revelolution).

I e-mailed Tero a week or week-n-half ago, and he still has not answered, so maybe someone here will know.


What is the max CPR count that the VSD-E can handle? I am using the SmoothStepper, so from what I have read, the limitations will be with the Drive??? Is that correct??



Thanks for the info



Steve

[H.O]

Hi Steve,
The limit isn't really in the resolution of the encoder per se. It's a fuction of the encoder resolution and the speed you need to get out of the motor. The VSD-E has an encoder count rate of 4MHz so if you go with a 1000 line encoder you should be able to get 60,000rpm. (4,000,000 * 60 / (1000*4))

I've personally used 3600lines encoders with the older VSD-A without problems, the motor are rated 2000rpm.

Make sure you get the encoder with differential line driver output - it'll be much more imune to noise than the single ended versions.

/Henrik.

[Jason3]

To add to Henrik's post, here's an exceprt from the VSD-E manual that might be helpful:

13. Motor compatibility

This is a short guide for determining whether or not a motor is suitable for VSD-E.

Motor type must be one of the following:
● Permanent magnet brushed DC
● Permanent magnet brushless DC (BLDC)
● Permanent magnet AC
● 2 or 3 phase stepping motor (3, 4,6 and 8 wire motors)

Servomotors must be equipped with an quadrature/incremental encoder with differential or single-ended (open
collector or TTL) outputs (see chapter Encoder). Stepping motors can be operated with or without encoder.

Encoder notes:
● 2 channel encoder is enough for all motor types
● Index channel is not required but is supported for precise homing
● Hall or commutation sensors are not required but are supported for AC/BLDC motors
● Suitable encoder resolutions are from about 100 PPR to 20000 PPR (pulses or lines per revolution)

Motor voltages and currents can introduce some limitations to motor output speed and torque but does not cause
unsuitability.
● Motor voltage is the limiting factor for maximum speed. For example, if you have a 100 VDC brushed DC
servo motor and run it at 70 VDC using VSD-E, then you can expect to get a speed of 88%*70V/100V = 61% of
motor's rated speed. 88% comes from VSD-E effective voltage swing at power outputs (see Electrical
specifications).
● Motor current is the limiting factor for maximum torque. For example, if you have motor rated for 20A DC
and drive's maximum output is 10A DC, then you get 50% of the rated torque.

VSD-E has dual range current sensing (HDRT, High dynamic range torque control) which makes it suitable also for very
small motors, such as ones with rated current around 100 mA.

Note: 200 VAC AC servo motors would reach about 20-30% of their rated speed on 80 VDC drive supply.

Regards,

Jason

[scrambled]

Thanks Jason3


The encoders are on the way!!!




Steve

[scrambled]

H.O.

Thanks for the information. I did not see your post until tonight.


Steve