Help
Subscribe to Bench Press
Leave Comment
One of the things we tried to do with the Motion Mind was pile on the functionality so it could do as many things as possible. At the same time we wanted to keep the cost as low as possible. The Motion Mind was a replacement for three products we previously produced... The ICON H-bridge, ICON Position Controller, and the ICON Interface Module.
Those three products could be arranged to produce a closed loop 32 bit DC motor position control system or an open-loop motor speed controller. With the Motion Mind we were able to reduce the retail cost of these systems by about 60% and provide similar functionality. We also included an RS232 port and analog inputs. This meant we could build into the Motion Mind firmware a closed-loop analog control system.
To operate in analog closed loop mode you need to set the DIP switches for mode 4 (MOD2 in left position, and MOD1, MOD0 in the right position). You will also need to adjust the PID settings to get good control.
Terms:
PID - Proportional, integral, and derivative controller.
PID Scalar - Adjusts the magnitude of the PID output.
Analog Feedback - Is usually a potentiometer connected to your mechanical system and lets the Motion Mind know the actual position of the motor.
Analog Control - Can be a potentiometer, an A/D output, or some other analog signal provides the Motion Mind with the desired position.
Example Schematic
Analog things-to-know:
There are some things to keep in mind when using the analog closed loop mode.
1. The input impedance of the analog inputs on the Motion Mind are around 2,500 ohms. So if you plan on using a potentiometer with a higher impedance then you may introduce some error to the system. You can isolate the impedance with an op-amp voltage follower external to the Motion Mind (see schematic).
2. The Motion Mind accepts analog signals from 0-5VDC, and converts them to a position value of 0-1023. This translates to 4.88mV per bit. The actual value will change somewhat based on the tolerance of the onboard 5V regulator. You can pull 5V and ground connections off of J4 to power the potentiometer as opposed to providing a separate source.
3. There is no analog front end filter to reduce electrical noise on the Motion Mind. If your system is noisy, and most motor systems are, you will lose some low end resolution. The 10-bits of position values may act more like 8 bits in practical use. If you need really precise postion control then it is best to use the serial closed loop mode with a quadrature (also called an incremental) encoder. That system provides 32-bits of position data.
4. The factory PID settings configured into the Motion Mind's memory are for serial PID control with a quadrature encoder. To use the analog system you will have to tune the PID, and generally the PID scalar value needs to be reduced from 14 to something closer to 12.
5. If the potentiometer is connected to your motor shaft it may spin in the reverse direction. Check that the spin of the shaft and the feedback potentiometer voltage at your wiper output match. When the motor is moving in reverse the wiper voltage should decrease. When the motor is moving forward the wiper voltage should increase. If this is reversed the motor will "run-away".
Video
The video below shows how to tune the analog PID setting. In it I use the Motion Mind 3, which is an rohs compliant prototype of the Motion Mind 2. In most respects it is the same product. To tune the PID you need to have the RS232 interface connected and the test software located on the Motion Mind product page installed on your PC.
The next steps mentioned in the video...
Those three products could be arranged to produce a closed loop 32 bit DC motor position control system or an open-loop motor speed controller. With the Motion Mind we were able to reduce the retail cost of these systems by about 60% and provide similar functionality. We also included an RS232 port and analog inputs. This meant we could build into the Motion Mind firmware a closed-loop analog control system.
To operate in analog closed loop mode you need to set the DIP switches for mode 4 (MOD2 in left position, and MOD1, MOD0 in the right position). You will also need to adjust the PID settings to get good control.
Terms:
PID - Proportional, integral, and derivative controller.
PID Scalar - Adjusts the magnitude of the PID output.
Analog Feedback - Is usually a potentiometer connected to your mechanical system and lets the Motion Mind know the actual position of the motor.
Analog Control - Can be a potentiometer, an A/D output, or some other analog signal provides the Motion Mind with the desired position.
Example Schematic
Analog things-to-know:
There are some things to keep in mind when using the analog closed loop mode.
1. The input impedance of the analog inputs on the Motion Mind are around 2,500 ohms. So if you plan on using a potentiometer with a higher impedance then you may introduce some error to the system. You can isolate the impedance with an op-amp voltage follower external to the Motion Mind (see schematic).
2. The Motion Mind accepts analog signals from 0-5VDC, and converts them to a position value of 0-1023. This translates to 4.88mV per bit. The actual value will change somewhat based on the tolerance of the onboard 5V regulator. You can pull 5V and ground connections off of J4 to power the potentiometer as opposed to providing a separate source.
3. There is no analog front end filter to reduce electrical noise on the Motion Mind. If your system is noisy, and most motor systems are, you will lose some low end resolution. The 10-bits of position values may act more like 8 bits in practical use. If you need really precise postion control then it is best to use the serial closed loop mode with a quadrature (also called an incremental) encoder. That system provides 32-bits of position data.
4. The factory PID settings configured into the Motion Mind's memory are for serial PID control with a quadrature encoder. To use the analog system you will have to tune the PID, and generally the PID scalar value needs to be reduced from 14 to something closer to 12.
5. If the potentiometer is connected to your motor shaft it may spin in the reverse direction. Check that the spin of the shaft and the feedback potentiometer voltage at your wiper output match. When the motor is moving in reverse the wiper voltage should decrease. When the motor is moving forward the wiper voltage should increase. If this is reversed the motor will "run-away".
Video
The video below shows how to tune the analog PID setting. In it I use the Motion Mind 3, which is an rohs compliant prototype of the Motion Mind 2. In most respects it is the same product. To tune the PID you need to have the RS232 interface connected and the test software located on the Motion Mind product page installed on your PC.
The next steps mentioned in the video...
Share This Entry:
0 Comments On This Entry
← September 2010 →
| S | M | T | W | T | F | S |
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | |||
| 5 | 6 | 7 | 8 | 9 | 10 | 11 |
| 12 | 13 | 14 | 15 | 16 | 17 | 18 |
| 19 | 20 | 21 | 22 | 23 | 24 | 25 |
| 26 | 27 | 28 | 29 | 30 |
Recent Entries
-
-
Analog Closed Loop Control
on Apr 08 2009 02:18 PM
-
-
-
