Limit Switch-Specific Home Position -1756-PLS

In addition to determining the relative zero point (home position) for the resolver’s axis, you may also determine a relative zero point for each limit switch. Three features determine a limit switch’s home position:

ZeroOffset

Use the ZeroOffset member when you know the starting point in the resolver’s axis. For example, if the limit switch’s zero position is at the machine’s 10 degrees point, to match the limit switch zero position to the machine zero position, you can configure the 1756-PLS module with a limit switch ZeroOffset value of 10 degrees.

The ZeroOffset value is limited to +/- the Rollover Position. For example, if you are using degrees as your engineering units, the maximum engineering units is 359 degrees. In this case, the ZeroOffset can be configured for values between -359 and +359.

The 1756-PLS module does not save ZeroOffset values after power-down. The value must be saved in the ControlLogix controller and downloaded to the 1756-PLS module with limit switch configuration data.

Preset

Use the Preset member to set the relative starting point for the limit switch by the energizing of an input.

For example, the 1756-PLS module can be configured to set the position to 0 degrees when an input turns ON. The 1756-PLS module replaces the current ZeroOffset value with this number.

When the Preset occurs, the 1756-PLS module changes the current Position to its Preset predefined value. The ZeroOffset value is recalculated by the 1756-PLS module. The new ZeroOffset value is temporary and remains until the next occurrence of the Preset.

The PresetInput member informs the 1756-PLS module which input on the module signals the Preset event.

Perform the following steps to use the Preset:

The Preset value is limited to less than or equal to the RolloverPosition. For example, if you are using degrees as your position units, the value of the Preset can range from 0 degrees to 359 degrees.

Nudge Up/Down

The Nudge Up/Down functions allow you to precisely adjust the 1756-PLS module’s Setpoints to account for minor changes in the machine set-up.

For example, during a shift, a resolver may have changed its position by +5 degrees due to slippage. The NudgeUp member allows you to correct the Setpoints by nudging up to the original position.

The Nudge Up Input ID informs the 1756-PLS module which input on the module uses the Nudge Up value configured with the message.

The Nudge Up Offset value determines the number of units (engineering) that are added to the Limit Switch Zero Offset when Nudge Up is used.

For example, if your application is using degrees for its engineering units, you can configure the Nudge Up Offset so that each time you use Nudge Up, the position change is +1 degrees. Thus, to move the zero offset 5 degrees, you click the nudge up button 5 times.

Nudge Down Input ID informs the 1756-PLS module which input on the module uses the Nudge Down value configured with the message.

The Nudge Down Offset value determines the number of units, engineering or raw, that are added to the Limit Switch Zero Offset when Nudge Down is used. This function works similarly to the Nudge Up Offset. Enter a negative Nudge Down Offset value to make Nudge Down decrease the position.