Quad - Step / Dir and resonance question

[mullenc525]

Hi,

I am looking to sync a stepper motor with a manual turntable (non-cnc side project). I am planning on using offset optical sensors to generate a quadrature output from the turntable, which will drive the stepper driver.

The stepper driver (http://store.qkits.com/moreinfo.cfm/QK158) takes a step and direction input. How can I convert quadrature to step and direction? Is there an IC that does this or do I need to work from scratch?

I am planning on using a 5718m-05s stepper (http://www.alltronics.com/mas_assets/acrobat/28M026.pdf). The maximum speed will be 0.5 rev/s, so I suspect I can run off a low voltage supply with no current limiter. The resistance times current rating equals 5V, how much extra voltage does the PS need to compensate for drops in the h-bridge?

Finally, I expect to run between 0 and 0.5 rev/s or 0-100 sps. The inertial load on the motor will be 1000x the motors inertia, with little friction (direct drive and ball bearings). Since the resonant frequency should decrease with the square root of inertia, I expect a new resonant frequency of 3 sps. Should I expect trouble?

Thanks!

[Mariss Freimanis]

1) We can modify the Verilog code for the G203V to accept a quadrature input (CH_A, CH_B instead of STEP, DIRECTION). We already have a CW, CCW code version for it.

2) Expect trouble with a 1,000:1 inertial load mismatch. The question is how much. Best case there will be considerable ringing and very sluggish accel/dec. Worst case the motor will be unable to move the load. Consider introducing some reduction gearing; the reflected moment of inertia is I / (reduction ratio)^2. A 5:1 reduction lowers the mismatch to a more reasonable 40:1.

Mariss

[mullenc525]

My required acceleration is 180 deg / s / s. The motor I am looking at has 20 times the required torque to accelerate my 1000:1 load at this rate. I assumed this would be ok, but I have no experience with these motors.

I have been considering sizing a damper to critically damp the system, to prevent resonance issues.

[mullenc525]

The reason I want to avoid gearing is I only have space for 100 marks on the turntable for the optical sensors. If I gear 5:1, I need 500 marks or I need to increase the step count by a factor of 5. The difficulty with increasing the step count by some factor is how do you time it so the steps are evenly spaced without some ugly hardware or a PIC (which I can avoid if I go direct drive and 1 step per optical mark)