RoboteQ AX2550 Closed Loop Position Mode, Safety limit switches interrupting power to motors

Closed Loop Position Mode

The diode polarity depends on the particular wiring and motor orientation used in the appli- cation. If the diode is mounted backwards, the motor will not stop once the limit switch lever is pressed. If this is the case, reverse the diode polarity.

The diodes may be eliminated, but then it will not be possible for the controller to move the motor once either of the limit switches has been triggered.

The main benefit of this technique is its total independence on the controller’s electronics and its ability to work in practically all circumstances. Its main limitation is that the switch and diode must be capable of handling the current that flows through the motor. Note that the current will flow though the diode only for the short time needed for the motor to move away from the limit switches.

SW1	SW2
	Motor

Controller

FIGURE 53. Safety limit switches interrupting power to motors

Another method uses the AX1500’s Emergency Stop input to shut down the controller if any of the limit switches is tripped. Figure 54 shows the wiring diagram used in this case. Each of the limit switches is a Normally Open switch. Two of these switches are typically required for each motor. Additional switches may be added as needed for the second 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.

88 AX1500 Motor Controller User’s Manual Version 1.9b. June 1, 2007