Command: Geared Slave Offset (35)

Supported Axes:	Position Control Axes
Supported Control Modes:	Position PID, Position I-PD

See the Commands Overview topic for basic command information and how to issue commands from PLCs, HMIs, etc.

Command Parameters

#	Parameter Description	Range
1	Slave Offset (position-units)	Any REAL number
2	Master Distance (position-units)	Any REAL number

Description

This command offsets the slave axis position by a specified amount. As the master moves the Master Distance from its position at the time this command was issued, the Slave Offset will be superimposed upon the slave position. When this command is issued, the axis must be geared and the gear ratio must be locked. This command will not work if the axis is geared with a Gear Absolute (25) command.

The Master Distance implies the direction with its sign. For example, with an initial master position 5, a Master Distance of 2 means that the offset will happen as the master moves from 5 up to 7. A Master Distance of -2 means that the offset happens from 5 down to 3.

The Geared Slave Offset command is related to the Phasing (34) command. The Phasing command shifts the master position as seen by the slave. The Gear Slave Offset command shifts the slave position itself.

Geared Slave Offset Example

In this example, Axis 1 (slave) is geared to Axis 0 (master) at a 1:2 ratio. Both axes start at 0 pu. The master is moving at 5 pu/sec. When the master reaches 2 pu, the following Geared Slave Offset command is issued to the slave.

Slave Offset = 1

Master Distance = 1

The plot below shows how the slave moves.

Legend: — Master Position —Slave Position — Slave Velocity — Master Velocity

The Initial Master and Slave positions are the positions at the time the command was issued. The Slave Final Position is 2.5 pu. If the Geared Slave Offset command had not been issued, it would have been at 1.5 pu at that master position. Therefore, the Geared Slave Offset moved the slave 1 pu, as specified by the command.

Reversing Direction

This command allows reversing the direction of the master. If the master reverses directions before the master has reached the Final Master Position, the slave will follow the profile in reverse. If the master continues in reverse past the Initial Master Position, no slave offset will be applied until the master returns to the Initial Master Position.

Once the master has reached the Final Master Position, the slave will continue gearing (as directed from the previous gearing command) whether the master goes forward or backward. It will not revert to the profile it followed before reaching the Final Slave Position.

Specifying an Absolute Position

The Master Distance parameter is relative to the master position at the time this command was issued. To specify an absolute position, use an Expression command that calculates the Master Distance by subtracting the current master position from the desired Final Master Position. For example, if the slave is gearing to the Axis 0 Target Position, and you wish to do the Slave Offset by the time the master reaches 5 pu, then use the following expression command:

MasterDist := 5 - _Axis[0].TarPos

where MasterDist is a variable defined in the variable table. Then use this variable in the Master Distance parameter of this command.

Rotary Axes

The Slave Offset and Master Distance specify distances on the axes. These distances are complete distances whether the axes are rotary or not. If both axes have a Position Unwind of 1, and the Slave Offset is 2 and the Master Distance is 3, the slave will be offset 2 pu, or 2 revolutions, while master moves 3 pu, or 3 revolutions. The sign of the values indicates the direction.

Target Generator State Bits

The Target Generator bits in the Status Bits register indicate which portion of the move the axis is currently in. These bits are useful when programming complex motion sequences.

Target Generator Done bit

Set when the master position has reached the Final Master Position. The gear ratio is now locked and will no longer change even if the master moves prior to the Final Master Position.

Target Generator State A and B bits

B	A	Description
0	0	The master is at or beyond the Initial Master Position. Use the Target Generator Done bit to determine if it has reached the Final Master Position.
0	1	Reserved
1	0	The master is prior to the Initial Master Position.
1	1	Reserved