MC_CamIn (FB)¶

FUNCTION_BLOCK MC_CamIn

Electronic Camming¶

The slave axis follows the movement of the master axis as defined by the given cam table.

This function block controls the Slave axis. The Master axis can be an axis controlled by another function block, or an encoder axis.

Calculation of slave positions¶

The positions for the Slave axis are calculated as follows:

Read the current position from the Master axis.

Scale and offset the master axis position to obtain the master cam position: MasterCamPosition = MasterScaling * MasterAxisPosition + MasterOffset

Evaluate the cam table at the master cam position to obtain the slave cam position: SlaveCamPosition = cam(MasterCamPosition)

Scale and offset the slave cam position to obtain the slave axis position: SlaveAxisPosition = SlaveScaling * SlaveCamPosition + SlaveOffset

Write the calculated slave axis position to the Slave axis.

Start Modes¶

Camming can be started in two different modes: immediate start and ramping in. With immediate start, the slave immediately follows the cam; with ramping in, a ramp-in phase is performed to bring the slave in sync with the cam.

Please note that the ramping-in start modes only have an effect on a rising edge of input Execute. If the cam table is changed by modifying input CamTableID, no ramping-in is performed.

Immediate Modes (absolute, relative)¶

With the start modes absolute and relative, the slave is InSync immediately and follows the cam table and master axis. Depending on the current state of the slave, this can lead to a jump in position, velocity, and/or acceleration.

If the StartMode is absolute, the value of SlaveAbsolute, set by MC_CamTableSelect, determines whether the start mode is abolute or relative. If the StartMode is relative, relative coordinates will be used for the slave position, effectively overwriting the value of MC_CamTableSelect.``SlaveAbsolute``.

In the diagram below, the start mode is absolute, the slave position (blue dots) jumps to the cam position (black line) immediately.

Ramping in with a Trajectory¶

With the start modes ramp_in, ramp_in_pos, and ramp_in_neg, the slave synchronizes to the cam as fast as possible using the configured VelocityDiff, Acceleration, Deceleration, and Jerk. If the slave is a modulo axis, ramp_in_pos and ramp_in_neg define the direction for ramping in. For a finite Slave, all three modes behave the same.

In the diagram below, the start mode is ramp_in. The slave position (blue dots) is ramped to the cam position (black line) and reaches it after the cam reaches the maximum position of 360.

Ramping in based on a Distance¶

With the start mode ramp_in_dist, the slave synchronizes to the cam so that it is InSync as soon as the master axis reaches the MasterSyncPosition. Synchronization will start when the master axis is within the MasterStartDistance of the MasterSyncPosition.

If MasterStartDistance is 0 (or negative), then the slave movement is started immediately, provided that the master is not in standstill. If BufferMode <> Aborting, then the MasterStartDistance must be 0 (or negative).

The MasterSyncPosition` must be a valid position in the cam table, otherwise the error SMC_CI_MASTER_SYNC_POSITION_OUT_OF_SCALE is reported.

In the diagram below, the start mode is ramp_in_dist. The master sync position is 180, and the master start distance is 0. The slave position (blue dots) is ramped to the cam position (black line) and reaches it exactly at master position 180, when the cam reaches the maximum position of 360.

Avoiding reversals of the slave axis¶

For some applications, a reversal of the slave axis is not allowed. For distance based ramping in, the input AvoidReversal will avoid a reversal of the slave during ramping in.

The avoidance is only applied to modulo slave axes. If a reversal cannot be avoided, the axis is stopped with an error.

Behavior:

If the slave axis is a modulo axis and the master velocity (times the slope of the cam table at the MasterSyncPosition) is not opposite to the slave velocity, then MC_CamIn tries to avoid a reversal of the slave. It tries to “stretch” the slave movement by increasing the distance the slave travels by up to 5 slave periods. If this “stretching” is not successful, i.e. does not avoid a reversal, an error is reported.

If the slave velocity is opposite to the master velocity times the slope of the cam table at the MasterSyncPosition, an error is reported.

If the slave axis is not a modulo axis, an error is reported on the rising edge of the Execute input.

Changing the Cam Table¶

Using the input `BufferMode`¶

The recommended way to execute a second cam table after a first one is to buffer a second instance of MC_CamIn with the second cam table.

When loading the second cam table with MC_CamTableSelect, MasterAbsolute and SlaveAbsolute both must be set to FALSE. The StartMode for the second MC_CamIn instance must be set to relative and the BufferMode to Buffered.

The second MC_CamIn instance will then start as soon as the first instance reports EndOfProfile while automatically making the transition as smooth as possible.

Changing the input `CamTableID`¶

Note

It is no longer recommended to change the cam table by changing the CamTableID.

For the recommended way to change the cam table on EndOfProfile see SwitchingCamsUsingBufferMode.
To immediately change the cam table simply restart MC_CamIn with BufferMode Aborting, the desired StartMode, and the new CamTableID.

While camming is active, this input can be used to change cam tables on the fly without a new rising edge on Execute. Compared to restarting camming with a rising edge on Execute, there are a few differences:

If ramping in with StartMode ramp_in, ramp_in_pos, or ramp_in_neg is active, it is not aborted.

Even if the StartMode is ramp_in, ramp_in_pos, or ramp_in_neg, no new ramping in is initiated.

If EndOfProfile has been set in the same cycle, the new cam table is automatically offset so that no gap occurs between the two tables.

Please note that when using distance based ramping in (ramp_in_dist), the error SMC_CI_CAM_CHANGED_DURING_RAMP_IN_DIST is returned if the CamTableID changes while ramping in is still active.

Tappets¶

Tappets can be evaluated using the function block SMC_GetTappetValue.

The input TappetHysteresis allows to define a hysteresis for the tappets of the cam table. A positive value means that the tappet cannot fire immediately after it has fired. The master position first needs to move away from the tappet by more than the value given for input TappetHysteresis.

For example, if the master is an encoder, the master position may oscillate by a few increments around the tappet position. Without a hysteresis, the tappet may fire all the time.

End of Profile¶

The output EndOfProfile indicates that the cam profile has been completed, either in positive or negative master direction.

For periodic cams, the output is set for one cycle for each new period.

For non-periodic cams, the output stays TRUE while the Master is outside the cam range. The Slave will remain in synchronized_motion. If the Slave is not in standstill when EndOfProfile is reached, another movement must be commanded that takes control of the Slave. MC_CamIn does not stop the Slave on EndOfProfile.

A buffered movement that has been commanded after this movement is started as soon as EndOfProfile is set. This behavior is the same for periodic and non-periodic cams.

Note that with StartMode ramp_in, ramp_in_pos, or ramp_in_neg and depending on the configured VelocityDiff, Acceleration, Deceleration, and Jerk, it is possible that the Master reaches EndOfProfile before the slave is InSync.

Note

MC_CamIn should be called after the motion FB controlling the Master axis has been called. Otherwise, the Slave axis will lag behind the Master axis.

InOut:

Scope	Name	Type	Initial	Comment
Inout	`Master`	AXIS_REF_SM3		Reference to master axis.
Inout	`Slave`	AXIS_REF_SM3		Reference to slave axis
Input	`Execute`	`BOOL`		Rising edge: Starts the execution of the function block.
	`MasterOffset`	`LREAL`		Offset on the master cam table position in master cam table units.
	`SlaveOffset`	`LREAL`		Offset on the slave axis position in slave axis units.
	`MasterScaling`	`LREAL`	1	Scaling factor for the master axis position. Must not be 0.
	`SlaveScaling`	`LREAL`	1	Scaling factor for slave cam position. Must not be 0.
	`MasterStartDistance`	`LREAL`		The master distance (in master cam table units) from the `MasterSyncPosition` where the slave axis starts synchronization. Only used in `StartMode` ramp_in_dist. See RampInDist.
	`MasterSyncPosition`	`LREAL`		The master position in the cam table where the slave axis has to be synchronized to the master. Only used in `StartMode` ramp_in_dist. See RampInDist.
	`AvoidReversal`	`BOOL`		`FALSE`: Signals that the reversal of the slave is physically possible and acceptable. `TRUE`: Signals that a reversal of the modulo slave has to be avoided, e.g. because it is physically impossible or might lead to damage. See AvoidReversal.
	`StartMode`	MC_StartMode	absolute	The start mode defines how the slave begins camming on a rising edge of input Execute. See StartModes.
	`CamTableID`	MC_CAM_ID		Identification of the cam table. The input is connected with the output of MC_CamTableSelect. See ChangingCamTableID.
	`BufferMode`	`MC_BUFFER_MODE`		Defines the chronological sequence of the FB relative to the previous block. Only the buffer modes `Aborting`, `Buffered` and `BlendingPrevious` are supported. A cam table can be executed after a single axis command such as MC_MoveAbsolute using the buffer modes `Buffered` or `BlendingPrevious`. `BlendingPrevious` means that the velocity (including the direction) of the previous movement is used as the blending velocity, even if this movement has the opposite direction compared to the cam table. For switching between cam tables, see SwitchingCamsUsingBufferMode. If the function block is Busy, then only the `BufferMode` `Aborting` is allowed.
	`VelocityDiff`	`LREAL`		Maximum velocity difference in u/s for `StartMode` ramp_in, ramp_in_pos, and ramp_in_neg.
	`Acceleration`	`LREAL`		Acceleration in u/s² for `StartMode` ramp_in, ramp_in_pos, and ramp_in_neg.
	`Deceleration`	`LREAL`		Deceleration in u/s² for `StartMode` ramp_in, ramp_in_pos, and ramp_in_neg.
	`Jerk`	`LREAL`		Jerk in u/s³ for `StartMode` ramp_in, ramp_in_pos, and ramp_in_neg.
	`TappetHysteresis`	`LREAL`		Size of the hysteresis for tappets in user units [u]. See Tappets.
Output	`InSync`	`BOOL`		Indicates that the `Slave` follows the cam profile.
	`Busy`	`BOOL`		Execution of the function block has not finished.
	`Active`	`BOOL`		Indicates that the FB has control on the axis
	`CommandAborted`	`BOOL`		Command has been aborted by another command
	`Error`	`BOOL`		Signals that an error has occured within the function block.
	`ErrorID`	`SMC_ERROR`		Error identification
	`EndOfProfile`	`BOOL`		Indicates that the `Master` has reached a start or end of the cam table. (Whether it is the start or the end depends on the direction of the master axis.) See EndOfProfile.
	`Tappets`	`SMC_TappetData`		Tappets: Has to be evaluated by SMC_GetTappetValue function block. See Tappets.