Motion Change Dynamics (MCD)

Use the Motion Change Dynamics (MCD) instruction to selectively change the speed, acceleration rate, or deceleration rate of a move profile or a jog profile in process.

Available Languages

Ladder Diagram

Function Block

This instruction is not available in function block.

Structured Text

MCD(Axis, MotionControl, MotionType, ChangeSpeed, Speed, ChangeAccel, AccelRate, ChangeAccelJerk, AccelJerk, ChangeDecelJerk, ChangeDecel, DecelRate, SpeedUnits, AccelUnits, DecelUnits, JerkUnits);

Operands

There are data conversion rules for mixed data types within an instruction. See Data Conversion.

Ladder Diagram and Structured Text

Structured Text

See

Structured Text Syntax

for more information on the syntax of expressions within structured text.

Enter your selection for the operands that require you to select your available options.

MOTION_INSTRUCTION Structure

Description

The MCD instruction changes the speed of profile moves on-the-fly and the speed, acceleration, and deceleration of trapezoidal profile jogs on-the-fly. Choose the desired physical axis and type of motion and enter values or tag variables for the Speed, Accel, and Decel. Speed, acceleration, and deceleration values can be entered as percentages of the current maximum configured value or directly in the configured speed or acceleration units of the axis.

If the targeted axis does not appear in the list of available axes, the axis has not been configured for servo operation. Use the Tag Editor to create and configure a new axis.

Programming Guidelines

In this transitional instruction, the relay ladder, toggle the Rung-condition-in from cleared to set each time the instruction should execute.

Changing Move Dynamics

When a Motion type of Move is entered or chosen, the speed, acceleration, and/or deceleration of a Move in progress may be changed to the specified value. The speed change occurs at the specified acceleration rate if the new speed is higher than the current speed or at the specified deceleration rate if the new speed is lower than the current speed.

Pausing Moves

The MCD instruction may be used to temporarily pause a move in progress by changing its speed to zero. Use another MCD instruction with a non-zero speed value to complete the move as originally specified.

Changing Jog Dynamics

When a Motion type of Jog is entered or chosen, the speed, acceleration, and/or deceleration of a Jog in progress may be changed to the specified value. The speed change occurs at the specified acceleration rate if the new speed is higher than the current speed or at the specified deceleration rate if the new speed is lower than the current speed.

Supporting Motion Drive Start (MDS) Instruction

The MCD instruction supports the Motion Drive Start (MDS) instruction. However, the MCD instruction has no affect on the DirectVelocityControlStatus Command feature because the Motion Planner only takes the value from the Direct Command Velocity Attribute and sums it into the axis output before sending the total command to the drive. After all acceleration and deceleration have been planned, the MCD instruction has no affect on the feature.

Changing Between MDSC and Time Driven Modes in Master Driven Speed Control (MDSC)

You cannot change from Master Driven Mode to Time Driven Mode or vice versa with an MCD instruction. You receive a runtime error if you attempt to change modes.

Affects Math Status Flags

No

Major/Minor Faults

None specific to this instruction. A major fault can occur if an uninitialized reference or a reference of incorrect type is passed to the Axis operand. See Common Attributes for operand-related faults.

Execution

Ladder Diagram

Structured Text

Error Codes

See

Motion Error Codes (.ERR)

for Motion Instructions.

Runtime Error Condition

For the Master Driven Speed Control (MDSC) function, an error will occur at runtime if you attempt to change the mode of the system from Master Driven to Time Driven or from Time Driven to Master Driven.

Extended Error Codes

Extended Error Codes provide additional instruction specific information for the Error Codes that are generic to many instructions. See

Motion Error Codes (.ERR)

for Motion Instructions.

Extended Error codes for the Parameter Out of Range (13) error code lists a number that refers to the number of the operand as they are listed in the faceplate from top to bottom with the first operand being counted as zero. Therefore for the MCD instruction, an extended error code of 4 would refer to the Speed operand’s value. You would then have to check your value with the accepted range of values for the instruction.

For the Error Code 54 – Maximum Deceleration Value is Zero, if the Extended Error returns a positive number (0-n) it is referring to the offending axis in the coordinate system. Go to the Coordinate System Properties General Tab and look under the Brackets ([ ])column of the Axis Grid to determine which axis has a Maximum Deceleration value of 0. Click on the ellipsis button next to the offending axis to access the Axis Properties screen. Go to the Dynamics tab and make the appropriate change to the Maximum Deceleration Value. If the Extended Error number is -1, this means the Coordinate System has a Maximum Deceleration Value of 0. Go to the Coordinate System Properties Dynamics Tab to correct the Maximum Deceleration value.

MCD Changes to Status Bits

For the Master Driven Speed Control (MDSC) function, when the MCD is executed (goes IP), the status bit (CalculatedDataAvailable (CDA)) is cleared in an MAM instruction, which indicates that the Event Distances has been computed. After the MCD is complete and the Event Distances have been recomputed, the CalculatedDataAvailable status bit is set again. Therefore, look at the CalculatedDataAvailable status bit after the MCD instruction has been completed to determine when to use the recomputed Event Distances.

If a MCD is executed, the CDA bit is cleared. The Calculated Data for the move is recomputed using the new dynamics parameters. The CDA bit is set again when computations are complete. The Calculated Data that is recomputed is measured from the original Motion Start Point (MSP) to the Event Distance point using the new dynamics parameters as changed by the MCD instruction - not from the point of the MCD.

Note that if the MCD changes the speed to 0, the Event Distance is not recomputed; the CDA bit is not set. The Event Distance is however recomputed if a second MCD is issued to restart the motion. The recomputed Calculated Data includes the duration of the stopped motion.

If the Event Distance is set to 0, the Calculated Data is set to equal the position that equals the length of the move. This may be one or two coarse update periods before the PC bit is set because of an internal delay. The end position is typically achieved in the middle of a coarse update period, which adds up to one additional coarse update period to the delay. Therefore, if the master is moved a distance equal to the Calculated Data, you must wait up to 2 iterations more for the PC bit of the slave move to be set.

Examples

Example 1

Ladder Diagram

Structured Text

MCD(Axis1,MCD_1,Move,Yes,75,Yes,50,No,0,No,0,No,0,%ofMaximum,%ofMaximum,%ofMaximum,%ofMaximum);

Example 2

Ladder Diagram

Structured Text

MCD(Axis1,mcd_motion_ctrl,Move,Yes,2,Yes,1,No,100,Yes,100.0,Yes,100.0,%ofMaximum,%ofMaximum,%ofMaximum,%ofTime);