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Command: Sync Move Absolute (13)

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

Command Parameters

Description

This command initiates a ratioed synchronized move on the axis. In this type of synchronization, the motion of all the axes in the same Sync Group are synchronized such that all the axes start and stop moving simultaneously, and at any point during the move, each axis has completed the same percentage distance (or ratio) of its move. For example, if three axes start at 0 inches, and are to move to 2, 4, and 6 inches, respectively, then at any point in the move, these axes' positions will be at a 1:2:3 ratio.

Synchronized moves are useful when several actuators are moving a rigid structure around a fulcrum. The axes do not need to start or stop at the same positions.

How to Start a Sync Move

To start a synchronized move, issue the Sync Move Absolute (13) or Sync Move Relative (14) commands simultaneously to each axis that you wish to include in the synchronized move. Refer to the Issuing Sync Move Commands Simultaneously section below. The Sync Group command parameter must be set to the same value for each axis to be synchronized together.

The Position, Speed, Acceleration, and Deceleration command parameters for all synchronized axes in the same group need not be the same. When the commands are issued, all the command parameters are evaluated and the RMC selects the maximum speeds and velocities for each axis such that (1) all axis positions are ratioed evenly throughout the move such that the axes arrive at the same time, (2) no individual axis exceeds its speed, acceleration, or deceleration parameters. Therefore, when issuing the Sync move, just set the velocities and accelerations to the maximum value you want on each axis, then the RMC will automatically ratio them so the axes remain in sync and arrive simultaneously.

For best results, all axes to be synchronized should be stopped when the Sync Move command is issued, although they are not required to be (this is required in firmware prior to 3.31.0). In closed loop control, "stopped" means the Target Velocity is zero; in open loop control, "stopped" means the Stopped Status Bit is be set. If the axes are moving (and not already synchronized) when a Sync Move is issued, this may cause discontinuities in the velocity and may jerk the axis. Changing directions while a sync move is in progress is not recommended.

Sync Group Details

The Sync Group command parameter is used to define which axes should be synchronized together. Valid group numbers are zero (0) to ten (10). It is possible to have multiple sync groups in progress at the same time. The sync group will be valid for the duration of the synchronized move. Once the Target Positions reach the Command Positions, the sync move will be complete, the axes no longer belong to that sync group, and the sync group number will be available for another synchronized move.

Changing a Sync Move In Progress

It is possible to speed up or slow down a sync move that is in progress while still maintaining the same synchronization ratio. To do so, issue sync move commands to all the synchronized axes such that the final position for each axis are the same as for the initial sync move command. It is not recommended that you change the final commanded positions of a sync move in progress. Doing so will likely cause a step jump in target speed on one or more axes, and is not allowed prior to 3.31.0 firmware.

Exiting a Sync Move In Progress

To remove an axis from a sync move in progress, issue any non-sync motion command to the axis. The motion of the remaining axes in the group will be re-evaluated based on their requested speeds and accelerations. This can cause the profile to speed up or use a different acceleration/deceleration value.

Synchronized Stop

If you need to stop a sync move in progress, use the Sync Stop (17) command to stop the axes while maintaining the synchronization.

Halting

If any axis in a sync group receives a Closed Loop Halt, then all axes in that sync group will halt while maintaining their sync ratios. When the halt is complete, the axes will no longer belong to the sync group. An Open Loop Halt or Direct Output Halt will immediately remove the axis from the sync group, and halt all the axis in that sync group with the same halt.

Notice that an axis can also be a member of a Halt Group as defined by the Halt Group Number axis parameter. Halts in any group will propagate recursively to other groups. If an axis halts, all axes in that group will halt, and so will the axes in any other sync groups or halt groups that the other axes in the group are part of.

S-Curves vs. Trapezoidal

If the Requested Jerk Axis Parameter is non-zero for any of the axes in the sync group, then all the axes will use s-curves. If the Requested Jerk Axis Parameter is zero for all of the axes in the sync group, then all the axes will use a trapezoidal profile.

When using s-curves, if the sync move commands are re-issued when the axes are decelerating, it may cause the axes to overshoot the requested positions.

Issuing Sync Move Commands Simultaneously

This section describes various methods of issuing the Sync Move commands simultaneously.

• From RMCTools
  In the Command Tool, set up the sync commands for each desired axis. Make sure all other axis have a No-op(0) command, then click the Send All button. If the Send All button is not visible, right-click in the Command Tool and choose Show Toolbar.

• From a User Program
  Including the Sync Move commands in the same step of a user program will ensure that they are issued simultaneously.

• From a Host Controller (PLC, HMI, etc.)
  The Sync Move commands must be written to the RMC such that they are all included in the same communication packet. Some PLCs and many HMIs are not capable of doing this. If this is the case, you will need to create a user program to issue the commands simultaneously. Then use the PLC or HMI to start the user program.

Status Bits

In Position Bit

When the Target Positions of all axes in the sync group reach their final positions, and the Actual Position of this axis is within the In Position Tolerance window, the In Position Status bit will be set. This bit indicates that the move is complete and the axis is at position.

Target Generator 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

This bit indicates that the Target Positions of all axes in the sync group have reached their final positions. Notice that this bit does not indicate whether the Actual Position has reached the Requested Position.

Target Generator State A and B bits

See Also

Sync Move Relative (14) | Sync Stop (17)

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