Daniel, Patrick, Matt
We did a little more rotation stage science today. The objective was to understand the remaining acceleration mystery, and to confirm that the resistor was helping. The on-screen EPICS values are the ones being used for acceleration and deceleration, and they now have an upper limit of 65000 (or 65s to reach the maximum speed of 100 RPM). Note that the on-screen velocity is in units of 0.01% of the maximum, so a value of 10000 gives the maximum speed of 100 RPM, and a value of 100 gives 1 RPM. (These RPM values are presumably for the motor, not the waveplate.)
We found that with the current firmware settings (which Patrick will append), the 50 Ohm resistor was not necessary, so we removed it. This means that other waveplates in the field need no hardware modification to achieve the 0.01dg accuracy we are seeing with this rotation stage.
The attached screenshot shows a move from 10W to 2W (velocity = 3000, acc = 6000, dec = 6000) and then from 2W to 10W (velocity = 300, acc = 60000, dec = 60000). Note that the higher values of acceleration and deceleration for lower velocities result in a smoother ride.
Current settings attached.
A couple of diagnostics features have been added to the code:
- Channels to look at the difference between measured and actual position (both counts and degrees)
- A channel which calculates the power from the measured angle
- Channels which look at the duty cycle and current of the PWM controller
- A halt flag which indicates that the rotation stage hasn't moved in the past 1 sec
- A busy error flag which indicates that the motor is no longer moving, but still indicating busy
- A tolerance value for the allowed angular error
- A target error flag which indicates that the tolerance has not been reached after the motor halted
- An auto abort button which, when enabled, will reset the busy flag after the busy error is lasting more than 2 sec
I reduced the calibration velocity from 3000 to 500. Driving too fast towards the home position seems to reduce its reproducibility. This test will have to be repeated by looking at the laser power.
The TCS rotation stages also got the new motor settings and can be tested. The TCS medm screens need to be updated as well. (why are they diffeerent?)