Motion Redefine Position (MRP)
CompactLogix
5380, CompactLogix
5480, ControlLogix
5580, Compact GuardLogix
5380, and GuardLogix
5580 controllersUse the Motion Redefine Position (MRP) instruction to change the command or actual position of an axis. The value specified by Position is used to update the Actual or Command position of Axis. The position redefinition can be calculated on an Absolute or Relative basis. If Absolute is selected the Position value is assigned to the current Actual or Command position. If Relative is selected the Position value is added as a displacement to the current Actual or Command position. The process of redefining the current axis position has no affect on motion in progress as the instruction preserves the current servo following error during the redefinition process. As a result, axis position can be redefined on-the-fly without disturbing axis motion.
Architecture and Safety Support
Available Languages
Architecture | Standard | Safety |
|---|---|---|
CompactLogix 5370, ControlLogix 5570, Compact GuardLogix 5370, and GuardLogix 5570 controllers | Yes | No |
Compact GuardLogix 5380, CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, and GuardLogix 5580 controllers | Yes | No |
Ladder Diagram
Function Block
This instruction is not available in function block.
Structured Text
MRP(Axis,MotionControl,Type,PositionSelect,Position);
Operands
Ladder Diagram and Structured Text
Operand | Type Tip: AXIS_CONSUMED is supported by Compact GuardLogix 5580, CompactLogix 5380, and CompactLogix 5480 controllers only. | Type Tip: AXIS_GENERIC is supported by the ControlLogix 5570 and the GuardLogix 5570 controllers only. | Format | Description |
|---|---|---|---|---|
Axis | AXIS_CIP_DRIVE
AXIS_VIRTUAL | AXIS_CIP_DRIVE
AXIS_VIRTUAL
AXIS_SERVO
AXIS_SERVO_DRIVE | Tag | Name of the axis on which to perform the operation. For controllers that support the REF_TO motion data types, the supported axis operand type can be replaced by an equivalent REF_TO type. |
Motion Control | MOTION_INSTRUCTION | Tag | Structure used to access instruction parameters. | |
Type | BOOLEAN | Immediate | The way you want the redefinition operation to work. Select either: 0 = absolute 1 = relative | |
Position Select | BOOLEAN | Immediate | Choose what position to perform the redefinition operation on. Select either: 0 = actual position 1 = command position | |
Position | REAL | Immediate or Tag | The value to use to change the axis position to or offset to current position. |
See
Structured Text Syntax
for more information on the syntax of expressions within structured text.For the operands that require you to select from available options, enter your selection as:
This Operand | Has These Options Which You | |
|---|---|---|
Enter as Text | Or Enter as a Number | |
Type | Absolute Relative | 0 1 |
PositionSelect | Actual Command | 0 1 |
MOTION_INSTRUCTION Structure
Mnemonic | Description |
|---|---|
.EN (Enable) Bit 31 | It is set when the rung makes a false-to-true transition and remains set until the servo message transaction is completed and the rung goes false. |
.DN (Done) Bit 29 | It is set when the axis' position action has been successfully redefined. |
.ER (Error) Bit 28 | It is set to indicate that the instruction detected an error, such as if you specified an unconfigured axis. |
Description
The MRP instruction directly sets the actual or command position of the specified axis to the specified absolute or relative position. No motion is caused by this instruction—the current axis position is simply redefined. Select or enter the desired Axis, Type, Position Selection, and enter a value or tag variable for the desired New Position.
If the targeted axis does not appear in the list of available axes, the axis has not been configured for operation. Use the Tag Editor to create and configure a new axis.
The MRP instruction may be used while the axis is moving as well as when it is at rest. MRP is used to redefine position on-the-fly for certain registration, slip compensation, and re-calibration applications.
Selection | Description |
|---|---|
Absolute Mode | When Absolute is selected or entered as the MRP Type, the New Position specifies the new absolute position of the axis. No motion occurs—the current axis position (actual or command) is simply redefined to be the specified new position. If software overtravel limits are used (refer to Motion Axis Object specification for more information on software overtravel configuration), the new position must be between the Max Positive and Max Negative Travel configuration values. Otherwise a software overtravel fault is generated when the instruction is executed. Important: If software overtravel limit checking is in effect, execution of an MRP in Absolute Mode may invalidate the current Max Positive and Max Negative Travel limits in the absolute sense. Exercise caution when redefining the absolute position of an axis that has travel limits.Absolute and relative mode MRP instructions have the same effect when the axis is not moving. When the axis is moving, however, absolute mode introduces a position error equal to the motion of the axis during the time it takes to execute the MRP instruction and assign the new position. Relative mode does not introduce this error and guarantees an exact correction independent of axis speed or position. |
Relative Mode | When Relative is selected or entered as the MRP Type, the New Position value is used to offset the current position of the axis. No motion occurs—the current axis position (actual or command) is simply redefined to be the current position plus the specified new position. In relative mode, axis position is redefined in such a way that no position errors are introduced if the axis is moving. It is particularly useful for unwinding axis position under program control rather than using the built-in rotary axis feature. Absolute and relative mode MRP instructions have the same effect when the axis is not moving. When the axis is moving, however, absolute mode introduces a position error equal to the motion of the axis during the time it takes to execute the MRP instruction and assign the new position. Relative mode does not introduce this error and guarantees an exact correction independent of axis speed or position. |
Actual Position | When Actual is selected or entered as the MRP Position Selection, the New Position is directly applied to the actual position of the physical axis. The command position of the axis is also adjusted along with the new actual position to preserve any position error which exists. This ensures that there is no unexpected motion of the axis when the positions are redefined. See the Motion Axis Object Specification for more discussion of command position, actual position, and position error. |
Command Position | When Command is selected or entered as the MRP Position Selection, the New Position is directly applied to the command position of the servo or imaginary axis. For an axis with a Position Loop type of Feedback Only, the Command Position and the Actual Position are the same. The MRP can be used with ether the Command or Actual Position with the same effect. The actual position of servo axes is also adjusted along with the new command position to preserve any position error which exists. This ensures that there is no unexpected motion of the axis when the positions are redefined. Command position is the desired or commanded position of a servo as generated by any previous motion instructions. Actual position is the current position of a physical or virtual axis as measured by the encoder or other feedback device. Position error is the difference between these two and is used to drive the motor to make the actual position equal to the command position. The Figure below shows the relationship of these three positions.  To successfully execute a MRP instruction, the targeted axis must be configured as either a Servo or Feedback Only axis. Otherwise, the instruction errs. Important: The instruction execution may take multiple scans to execute because it requires multiple coarse updates to complete the request. The Done (.DN) bit is not set immediately, but only after the request is completed. |
In this transitional instruction, the relay ladder, toggle the Rung-condition-in from cleared to set each time the instruction should execute.
Master Driven Speed Control (MDSC) and the MRP Instruction
You can execute an MRP on the Master or the Slave axes or coordinate system when an MDSC is active.
The Master axis position is changed when an MRP is executed (goes IP) on the Master while it is moving in MDSC mode; the slave is not affected.
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
Condition/State | Action Taken |
|---|---|
Prescan | The .EN, .DN, .ER, and .IP bits are cleared to false. |
Rung-condition-in is false | The .EN bit is cleared to false if the .DN or .ER bit is true. |
Rung-condition-in is true | The .EN bit is set to true and the instruction executes. |
Postscan | N/A |
Structured Text
Condition/State | Action Taken |
|---|---|
Prescan | See Prescan in the Ladder Diagram table. |
Normal execution | See Rung-condition-in is false, followed by rung is true in the Ladder Diagram table. |
Postscan | See Postscan in the Ladder Diagram table. |
Error Codes
See Error Codes (ERR) for Motion Instructions.
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. The following Extended Error codes help to pinpoint the problem when the MRP instruction receives a Servo Message Failure (12) error message.Associated Error Code (decimal) | Extended Error Code (decimal) | Meaning |
|---|---|---|
SERVO_MESSAGE_FAILURE (12) | Device in wrong state (16) | Redefine Position, Home, and Registration 2 are mutually exclusive. |
Extended Error codes for the Parameter Out of Range (13) error code work a little differently. Rather than having a standard enumeration, the number that appears for the Extended Error code 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 MRP instruction, an extended error code of 4 would refer to the Position operand’s value. You would then have to check your value with the accepted range of values for the instruction.
MRP Changes to Single Axis Status Bits
The AxisHomedStatus bit is not impacted by the execution of the MRP instruction. The status is the same before and after the MRP is execution. If the axis has been homed using the absolute home procedure, the AbsoluteReferenceStatus is set. AxisHomedStatus may also be set is the axis has not been subject to a power cycle. AbsoluteReferenceStatus is cleared when the MRP is executed and this is only true to Axis_Servo_Drive axis. This indicates the axis position is no longer referenced to the absolute home position.
Examples
Example 1
Ladder Diagram
Example 2
Ladder Diagram
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