RoboteQ AX2550/2850 user manual Using Current Limiting as Protection, Control Loop Description

Closed Loop Position Mode

The second method uses the AX2500/2850’s Emergency Stop input to shut down the con- troller if any of the limit switches is tripped. Figure 72 shows the wiring diagram used in this case. Each of the limit switches is a Normally Open switch. Two of these switched are typically required for each motor. Additional switches may be added as needed for the sec- ond motor and/or for a manual Emergency Stop. Since very low current flows through the switches, these can be small, low cost switches.

The principal restriction of this technique is that it depends on the controller to be fully functioning, and that once a switch is activated, the controller will remain inactive until the switch is released. In most situations, this will require manual intervention. Another limita- tion is that both channels will be disabled even if only one channel caused the fault.

Manual

Emergency

Stop Switch

SW1

Ground

SW2

Motor

AX2550

Emergency Stop Input

FIGURE 72. Safety limit using AX2500/2850’s Emergency Stop input

Important Warning

Limit switches must be used when operating the controller in Position Mode. This will significantly reduce the risk of mechanical damage and/or injury in case of dam- age to the position sensor or sensor wiring.

Using Current Limiting as Protection

It is a good idea to set the controller’s current limit to a low value in order to avoid high cur- rent draws and consequential damage in case the motor does not stop where expected. Use a value that is no more than 2 x the motor’s draw under normal load conditions.

Control Loop Description

The AX2500/2850 performs the Position mode using a full featured Proportional, Integral and Differential (PID) algorithm. This technique has a long history of usage in control sys- tems and works on performing adjustments to the Power Output based on the difference measured between the desired position (set by the user) and the actual position (captured by the position sensor).

120 AX2500/2850 Motor Controller User’s Manual Version 1.7. February 1, 2005