Modulo Axis

Modulo axis positioning is a motion control method used for rotary axes where positions repeat after a full cycle. In a rotary axis with a modulo range of 0° to 360°, if the axis moves past 360°, the position resets to 0° instead of continuing to 361°. Similarly, moving backward past 0° would wrap around to 359° instead of going to -1°.

NOTE: Starting with KS 4.5.2, modulo axis is supported.

KINGSTAR Modulo Axis Example

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// MoveAxisAbsolute, shortest path

KsCommandStatus moveCommand{};
KsCommandStatus setParaCmd{};
KsCommandStatus setPosOffsetCmd{};
 
setParaCmd = SetAxisParameter(TargetAxis, McAxisParameter::mcModuloAxisValue, 360, McExecutionMode::mcImmediately);
setParaCmd = WaitForCommand(10, true, setParaCmd);
 
setParaCmd = SetAxisParameter(TargetAxis, McAxisParameter::mcEnableModuloAxis, TRUE, McExecutionMode::mcImmediately);
setParaCmd = WaitForCommand(10, true, setParaCmd);
 
setPosOffsetCmd = SetAxisPositionOffset(TargetAxis, 0, FALSE, McExecutionMode::mcImmediately);
setPosOffsetCmd = WaitForCommand(10, true, setPosOffsetCmd)
 
moveCommand = MoveAxisAbsolute(TargetAxis, 360, 360, 3600, 3600, 360000, McDirection::mcShortestWay, McBufferMode::mcBuffered); // A
moveCommand = MoveAxisAbsolute(TargetAxis, 720, 360, 3600, 3600, 360000, McDirection::mcShortestWay, McBufferMode::mcBuffered); // B
moveCommand = MoveAxisAbsolute(TargetAxis, 60,  360, 3600, 3600, 360000, McDirection::mcShortestWay, McBufferMode::mcBuffered); // C
moveCommand = MoveAxisAbsolute(TargetAxis, 340, 360, 3600, 3600, 360000, McDirection::mcShortestWay, McBufferMode::mcBuffered); // D
moveCommand = MoveAxisAbsolute(TargetAxis, 90,  360, 3600, 3600, 360000, McDirection::mcShortestWay, McBufferMode::mcBuffered); // E

This code example configures and controls a modulo rotary axis in a motion control system by:

Configuring the axis as a modulo axis by assigning a modulo axis value of 360 and enabling modulo axis.
Commanding the axis to move to five absolute positions using MoveAxisAbsolute, ensuring the shortest path is taken.

The diagram above illustrates the movement for each command:

Command	Start Position	Target Position	Movement Distance (Direction)	Modulo Mode Effect
A	0°	360°	0°	360 % 360 = 0 Since the axis is currently at 0°, no movement occurs.
B	0°	720°	0°	720 % 360 = 0 Since the axis is currently at 0°, no movement occurs.
C	0°	60°	60° (Positive)	60 % 360 = 60 The axis is currently at 0°, and the shortest way to 60° is moving 60° in the positive direction. If it moves in the negative direction, it would travel 300°, which is much longer.
D	60°	340°	80° (Negative)	340 % 360 = 340 The axis is currently at 60°, and the shortest way to 340° is moving 80° in the negative direction. If it moves in the positive direction, it would travel 280°, which is much longer.
E	340°	90°	110° (Positive)	90 % 360 = 90 The axis is currently at 340°, and the shortest way to 90° is moving 110° in the positive direction. If it moves in the negative direction, it would travel 250°, which is much longer.

KINGSTAR Modulo Axis

The content in this section includes information you should know about modulo axis in KINGSTAR.

To configure KINGSTAR modulo axis, use the mcEnableModuloAxis and mcModuloAxisValue parameters.
- For RT/Win32, see McAxisParameter
- For .NET, see McAxisParameter

When modulo axis is enabled, position input and output in the following APIs will be converted to modulo position:

When modulo axis is enabled, distance input in the following APIs will NOT be converted with the modulo settings:

When modulo axis is enabled, position input in the following APIs will NOT be affected by the modulo settings:
- SetAxisCyclicSwitch
- SetAxisCam
- SetTrigger (users are responsible for converting the trigger value to a modulo value)

The Group motion APIs can't be used with modulo axis.

Properties of converted modulo value:
- The converted modulo value is always positive (0, modulo_value]. For example, assume the modulo value is set to 360. If a user commands a target position of -20, KINGSTAR will interpret it as 340.
- The default modulo value is UINT_MAX.
- No error is returned when a positive or distance command exceeds the modulo range.
- When the axis is at position 0 (modulo_value), the actual position may drift slightly away from 0. For example, assume the modulo value is set to 360. If a position is drifting by -0.001, the user will get a position of 359.999.

Drive's modulo feature:
- It is not recommended to enable the drive's modulo feature, as drives should be recognized as linear axes.
  - Take Sanyodenki's RS3 as an example, the drive's modulo feature relies on 0x607B (CiA), which is an optional object that is not guaranteed to be present.
  - If users still want to use the drive's modulo feature, we recommend that users:
    - Turn off the KINGSTAR modulo axis.
    - Maintain the modulo position on their own.