This function is used to slave the position of an axis (called the slave axis) to the position of another axis from the same module (called the master axis).
The master axis is always the axis 0. A 2 axis module can have one master axis and one slave axis. A 4 axis module can have one master axis and up to 3 slave axes.
This position slave function is confirmed in the configuration screen. At programming level, the slave axis is slaved to the master axis when the SLAVE bit (%Qr.m.c.17) of this axis is set at 1. The IN_SLAVE bit (%Ir.m.c.36) indicates that the slave axis is operating in tracking mode.
An axis is slaved either to the measured position or to the master axis position setpoint (choice defined in the configuration screen). A RATIO1 / RATIO2 ratio and an Offset are applied to obtain the final setpoint. These 3 parameters are defined in the adjustment screen.
The slave axis is related to the master axis in the following way:
SlavePositionSetpoint = MasterPosition x (Ratio1 / Ratio2) + SlaveOffset
In order to indicate that the slave axis is tracking the master axis correctly, the AT_PNT (%Ir.m.c.9) bit from the slave axis is set at 1 when the slave has caught up with the master and remains close to it (tracking error of the latter is lower than DMAX2) for more than TSTOP ms
Differences from the TSX CAY •1 Module
The tracking function of a TSX CAY•2 module differs from the TSX CAY •1 in the following ways:
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the ratio can be modified from the application or by the P_Unit in recalibration mode (for the TSX CAY •1 module the ratio is set during configuration,
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the offset enables to slave axis to slave itself to the master axis, whatever the master’s position. This allows object tracking applications to be set up where a tool-carrying axis has to be slaved to a permanently moving axis (conveyor) for the transportation of objects (glue application, etc.).
The offset value can be modified from the application or from the P_Unit software in recalibration mode. The TSX CAY •2 module provides an alignment or locking device in order to avoid a ’surprise’ during the switch to slave mode.
The function calculates the offset as follows:
SlavePosition = MasterPosition X Ratio + Offset
The configuration parameter Automatic offset is used to select the operating mode. The signed ratio value advances from 0.01 and 100.
Parameters Associated with the Master Mode - Slave
The parameters of the master – slave mode are as follows:
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Ratio1 (%MWr.m.c.29) and Ratio2 (%MWr.m.c.30) which determine the value of the master – slave ratio,
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Slave_Off (%MDr.m.c.55): offset value when the Automatic offset option has not been selected during configuration,
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InternalSlaveOffset: offset value (calculated by the module and not accessible by the user) when the Automatic offset option has been selected during configuration,
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The master axis is configured in automatic or manual mode in the framework of a setpoint follower.
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The slave axis is referenced in automatic mode.
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No blocking fault is detected.
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The master axis must be referenced within the framework of a measurement follower (the master being situated indifferently in one of the 4 modes).
If the calculated setpoint overshoots the axis soft stops, the moving part stops and the command is refused.
SlavePositionSetpoint = MasterPosition (1) x Ratio1 / Ratio2 + Slave_Off (or InternalSlaveOffset)
(1) according to configuration.
This mode is used to slave a slave axis to a master axis. In this case, the slave is declared a measurement follower.
Meaning of the AT_PNT Bit and DMAX2 Parameter
The DMAX2 parameter defines the precision threshold.
This value is particularly useful in the object tracking applications where the slave axis goes into a recovery phase before satisfying the condition:
(MasterPosition x Ratio + Offset) - DMAX2 < or = (SlavePosition) < or = MasterPosition x Ratio + Offset) + DMAX2
As soon as the condition is satisfied over a period at least equal to the value of the T_STOP parameter, the AT_PNT bit takes the value 1, to signify that the slave axis has caught up.
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For the calculated slave axis position setpoint to be valid, you must make sure that the slave axis is already at the Master x RATIO position before switching this axis to slave mode.
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Reference point commands on the master axis must be avoided when there are slave axes (risk of tracking error fault on the slave axis).
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In Tracking mode:
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the TH_PNT, NEXT information bits are not managed,
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the PAUSE command is not active,
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CMV modifications are not taken into account (CMV = 1000).
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When a slave axis is slaved to a master axis, the slave tries to catch up with the master by the shortest possible route. For this reason, the tracking error must always be less than half the slave modulo value.
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During configuration you can specify that the link between slave and master must be made with no movement.
In this case, the slave does not take the SlaveOffset parameter into account, and calculates an InternalSlaveOffset parameter (which is not communicated to the application), in order to inhibit all slave movements, at the point when it becomes a slave, while the master is immobile.
These applications are made up of:
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an infinite axis or "master axis" which moves continuously,
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an axis which is sometimes controlled by a master, and sometimes independent.
