After downloading the motor configuration file to a Gemini, the motor will be optimized for the no load condition. This means that by adding any load to the shaft the tuning will not be optimal. To adjust for your load use the following procedure.
1) Enter the LJRAT value for the system. LJRAT is the load to rotor inertia. During the sizing process this should have been calculated. If not, then one must calculate it based on physics formulas found in any physics book, the Engineering Reference Section of the Compumotor Catalog, or online. The rotor inertia is found in the Rotary Servo Motors section of the Compumotor Catalog or online under the motor series.
2) Enter the LDAMP value for the system. LDAMP is the system damping provided by the mechanical load. If the system has significant damping from the load but one does not know the exact value, adjust this value until the desired performance is achieved. If the system does not have significant load damping, leave the LDAMP value at 0.
Check the system performance by performing moves that are close to those that will be done in the working system. If the performance is adequate, stiffness and lack of oscillation are present, then the drive is tuned. If there are oscillations, high pitch noises, or sluggish responses to commanded motion, then proceed to the next step in this procedure.
3) Disable the drive and type DMODE17. This is position tuning mode and the drive will turn the motor 1/4 of a revolution back and forth. If you have an oscilloscope then connect it to the 2 analog monitors on the 50 pin connector: An oscilloscope is not required, but will more accurately depict current performance.
Pin 21 = Channel A configured with DMONAV
Pin 22 = Channel B configured with DMONBV
Pin 25 = Analog Ground
Connect one channel of the oscilloscope to Channel A on the Gemini and the ground to Analog Ground; type DMONAV3 to set Channel A analog monitor to display the position error. Adjust the scale on the oscilloscope to display the analog voltage.
Enable the drive and observe the system response. Position Error will increase during acceleration, but should smoothly decay to near zero without significant ringing or oscillations. If ringing or oscillations are observed then do the following:
- Decrease DPBW
- Increase the Position Mode damping with SGPRAT
- Decrease SGPSIG
- For applications with high static friction or backlash, turn off the integrator with SGINTE0
- If these all fail, make sure LJRAT and LDAMP are set appropriately.
If a sluggish response is observed, the position bandwidth is set too low, or the position mode damping is set too high.
- Increase DPBW
- Decrease SGPRAT
- Increase SGPSIG
Adjust these factors until performance is adequate. Check the system performance by performing moves that are close to those that will be done in the working system. If the performance is adequate, stiffness and lack of oscillation are present, then the drive is tuned. If there are oscillations, high pitch noises, or sluggish responses to commanded motion, then proceed to the next step in this procedure.
4) Disable the drive and type DMODE15, current loop tuning mode. In this mode the drive commands a 10 Hz step change in current proportional to the motor's continuous current setting (DMTIC). No motion will occur so this procedure will require an oscilloscope. Type DMONAV16 for commanded current and DMONBV17 for actual current. Connect the oscilloscope to both analog monitor channels on the Gemini.
Enable the drive; please note that motion doesn't necessarily occur, but can since there is current in the motor. Sudden motion of the motor must be expected.
Adjust the oscilloscope to see the commanded and actual currents in the motor. If ringing, audible high pitched noise or oscillations are observed, do the following:
- Decrease DIBW
- Increase SGIRAT
A sluggish response indicated the bandwidth is set too low or the damping is set too high.
- Increase DIBW
- Decrease SGIRAT
After adjusting to get adequate performance, redo number 3. Once these are both done, check the system performance by performing moves that are close to those that will be done in the working system. If the performance is adequate, stiffness and lack of oscillation are present, then the drive is tuned. If there are oscillations then proceed to the appropriate Hardware Installation Guide for instructions on how to use the Filters to eliminate mechanical resonances.