In this follow-up to the previous article, we continue exploring dual-axis control using the CMZ motion controller “FCT641” with CODESYS SoftMotion and OMRON servo drives (R88D-1SN01L-ECT) over EtherCAT.

This time, we focus on MC_GearIn / MC_GearOut to demonstrate master-slave axis synchronization (gear control).
We’ll walk through key topics such as velocity ratio tracking, coupling/decoupling timing, and hands-on HMI-based operation for intuitive testing and tuning.

Come on, let’s enjoy FA!

Reference Link

Codesys# Let’s Implement 2-axis control by via CMZ FCT641 and OMRON servo!

MC_GearIn (FB)

MC_GearIn is a function block that links a slave axis (driven axis) to a master axis (main axis) and applies a constant speed ratio between the two axes.

Once this block is initiated, the slave axis is gradually accelerated to the specified ratio of speeds, and when the target speed ratio is reached, coupling (coupling) with the master axis is complete.

At this time, the distance traveled until coupling is established is not compensated (the misaligned distance remains unchanged).

Notes

MC_GearIn must be executed after the function block of the motion system that controls the master axis (e.g., MC_MoveVelocity, MC_MoveAbsolute, etc.) is called.Otherwise, the slave axis will lag behind the master axis.
If the speed ratio needs to be changed during MC_GearIn operation, it can be changed by calling MC_GearIn again.In this case, a prior call to MC_GearOut is not necessary.
When the specified speed ratio is reached, the output flag InGear is set; the coupling mechanism after InGear is set depends on the axis’ current control mode.

interface

input-output（Inout）

name	Type	initial value	Description.
Master	AXIS_REF_SM3	–	Master axis (spindle) axis reference.The master axis does not necessarily have to be stopped.
Slave	AXIS_REF_SM3	–	This is an axis reference for the slave axis (driven axis).

input（Input）

name	Type	initial	Description.
Execute	BOOL	–	On the rising edge (0 to 1), the GearIn function starts executing.
RatioNumerator	DINT	1	Numerator for specifying the target speed ratio of the master and slave axes in fractional form.
RatioDenominator	UDINT	1	Denominator of the target speed ratio.For example, if the numerator is “1” and the denominator is “2,” the slave axis will have half the speed of the master axis.
Acceleration	LREAL	–	This is the maximum acceleration to allow the slave axis to reach the target velocity ratio.[Unit: u/s²].
Deceleration	LREAL	–	This is the maximum reduced speed to allow the slave axis to reach the target speed ratio.[Unit: u/s²].
Jerk	LREAL	–	This is the maximum jerk (rate of change of acceleration) when the slave axis is accelerating or decelerating.[Unit: u/s³].
BufferMode	MC_BUFFER_MODE	–	This mode specifies the chronological order of this FB’s actions with the previous action

Output（Output）

名称	Type	initial value	Description.
InGear	BOOL	–	In the case of TRUE, the slave axis has reached the set speed ratio and coupling (coupling) is established.
Busy	BOOL	–	If TRUE, it indicates that this function block is currently being executed (processed).
Active	BOOL	–	Indicates that this function block has control authority over the slave axis.
CommandAborted	BOOL	FALSE	When TRUE, it indicates that the operation of this function block has been interrupted by an interrupt by another FB, etc.
Error	BOOL	–	If TRUE, it indicates that an error occurred during the processing of this FB.
ErrorID	SMC_ERROR	–	When an error occurs, this identification code indicates the detailed type of error.

Example

This figure shows the transition of each signal and axis speed when the MC_GearIn function block is executed twice consecutively.

FB Settings

Here is an example of GearIn FB in use.

1st GearIn

For the first GearIn, the Ratio: ratio is “1”, i.e., the slave axis runs at the same speed as the master axis.

Second GearIn

The second GearIn is Ratio: the ratio is “2”, i.e., the slave axis runs at twice the speed of the master axis.

time chart

The overall process is,

The first GearIn is performed and the slave axis accelerates until it reaches the same speed as the master axis.
When the set speed (ratio “1”) is reached, InGear is set.
Once Execute is turned off, the coupling is de-coupled.
When the second GearIn is executed, the slave axis is further accelerated and reaches twice the speed of the master axis.
InGear is set again, and a new ratio (ratio “2”) is used for the coupled state

First.Execute (first execution instruction)

When first set to ON (1), the GearIn operation starts; when set to OFF (0), the GearIn operation ends (stops).

First.InGear (1st speed ratio achieved signal)

It turns ON when the slave axis reaches the set ratio (here “1”).Once turned ON, it is held until Execute is turned OFF.

Second.Execute (second execution instruction)

After the first Execute is turned OFF, it is turned ON again to start the next GearIn operation.

Second.InGear (second speed ratio achieved signal)

It turns ON when the next set ratio (in this case “2”) is reached.

MySlave.Velocity (velocity of slave axis)

Finally, let’s look at the speed of Slave: after the first run, the speed gradually increases, following the speed of the master axis, achieving a ratio of “1”.After the ratio is achieved, the speed changes temporarily when Execute is turned off.

The next time the second Execute is turned on, the speed increases further, eventually reaching a ratio of twice the master axis speed.

MC_GearOut

MC_GearOut is a function block that disconnects (unlinks) a slave axis (driven axis) from a master axis (spindle).When this block is executed, the slave axis is disconnected from the master axis to which it was previously connected.

Notes

It is usually assumed that some other movement command (e.g., MC_Stop or MC_GearIn) will be executed after this block.
If no move command is specified after MC_GearOut, the slave axis will default to “maintain the previous speed.In other words, the slave axis will continue to move at the same speed after uncoupling, so it is recommended that the subsequent process be explicitly specified to prevent unintended movement.

interface

input-output（Inout）

name	Type	Description
Slave	AXIS_REF_SM3	This is an axis reference for the slave axis (driven axis).

input（Input）

name	Type	Description
Execute	BOOL	Execution of GearOut (decoupling) operation starts at the rising edge (0→1).

Output（Output）

名称	型	説明
Done	BOOL	When TRUE, it indicates that the axis has been successfully decoupled.
Busy	BOOL	If TRUE, it indicates that the processing of this function block has not yet been completed (is in process).
Error	BOOL	If TRUE, it indicates that an error occurred during the execution of this FB.
ErrorID	SMC_ERROR	When an error occurs, the error code indicates the type of error.

Implementation

Variable Declaration

This one controls two axes (_Axis1 and _Axis2) and also declares instances for gear connection (MC_GearIn) and disconnection (MC_GearOut) between axes.

PROGRAM pAxis
VAR

_Axis1: fbAxis;
_Axis2: fbAxis;
_AxisGear :SM3_Basic.MC_GearIn;
_AxisGearOut:SM3_Basic.MC_GearOut;
END_VAR

Program

This is an addition to the previous program, using MC_GearIn to link slave axis _Axis2 to master axis _Axis1 with a velocity ratio, and the slaves follow at the speed of RatioNumerator : RatioDenominator.Also, use MC_GearOut to decouple if necessary.