ORCA™ motors have five modes of operation: Sleep Mode, Force Mode, Position Mode, Haptic Mode and Kinematic Mode. This Iris Tutorials will cover how to get started with Position Mode. In our previous tutorial we introduced Force Mode, a mode in which the user controls the force output of the ORCA motor by inputting a desired target force. The motor will apply the target force to the shaft, independent of position. Position mode is another layer of control above force mode. The user inputs a desired end position for the motor’s shaft, and the motor generates the required force to move the shaft to that position.
Before entering Position Mode (3), the user should make sure the shaft has been zeroed to a known position, either manually or through the autozeroing feature. To learn more about autozeroing, watch our short tutorial here.
Position Mode is especially useful to applications when precise control over the shaft's position is required, for example, when simulating a physical control surface or actuator that must stop at exact points.
Position mode is the third mode of the motor’s operation. To enter Position mode a serial connection is required, in this case we are using a Modbus connection. Once in position mode, communications must be made regularly over the Modbus interface to avoid a timeout error. In the event of communications failure or other motor errors, the motor will cease all power draw and put the windings into a passive braking effect.
In order to tune the PID controller, go to the position/kinematics page on IrisControls.
| Fmax | Maximum amount of force that the position controller will output, measured in millinewtons |
| P | Proportional gain |
| I | Integral gain |
| DV | Derivative of velocity |
| DE | Derivative of error |
The green numbers represent active values, and the white numbers represent the staged setting.
For example, if we want to increase the value for ‘P’, we change the staged setting to 1500. The active value does not change until we click apply tuning. Then the active value rises to meet the staged setting. Tuning will also be automatically applied when entering any position control mode.
The amount of time the active value takes to rise depends on the softstart duration, which can be changed by the user in order to be faster or slower.
In position mode, the internal PID control loop will always attempt to directly follow the last position command. This means a high-speed serial connection is essential for smooth position mode operation.
Smooth position control can still be achieved with low speed Modbus communication, or our in-house GUI IrisControls using Kinematic mode, which we will cover in depth in our next video tutorial.