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HARSFEN0602
This block stops the desired position reference to its present position if a hard-stop switch is
sensed.
Right Limit Switch (Marked as 3 in the Figure)
This block stops the desired position reference to its present position if an RLS switch is
sensed, and if the output of the position reference generator is less than the controller's
position command.
Forward Limit Switch (Marked as 4 in the Figure)
This block stops the desired position reference to its present position if an FLS switch is
sensed, and if the output of the position reference generator is greater than the controller's
position command.
Rate and Acceleration (Marked as 5 in the Figure)
This block limits the speed and the acceleration of the controller's position command. The
block limits both the acceleration and the deceleration to the parameter SD, and the speed
command (the derivative of the position command) is limited to VL[2] from below, and
VL[3] from above.
The rate and acceleration limiter block intervenes in the following situations:
The position command to the controller experiences an abrupt change – for example
when a hard-stop switch is sensed, or when a hard-stop switch is released
The reference generator tries to command the motor in the permitted position range,
but with too great speed.
The position command moves towards its permitted boundary (VL[3] or VH[3])
with speed greater then can be braked until the boundary with SD acceleration. For
example, near VH[3], the upper speed limit may be much smaller then VH[2].
When the position command equals VH[3], the maximum allowed speed command
is zero.
Example
In this example, the software reference generator generates a sine, using PVT.
The low position limit is VL[3]=-5000. The input to the Stop Manager and its output (the
position command to the controller) are depicted in Figure 33 below. The input of the Stop
Manager (The output of the position reference generator) is in red, and the output of the Stop
manager is in dashed green. In At the time of 0, the PVT starts at the position of 17000. The
Stop-Manager catches up with the sinusoidal command, with the acceleration limit of SD.
At the time of 1sec, a hard-stop switch becomes active, and remains active until the time of
1.2 sec. The Stop manager decelerates the position command to zero speed, using the
deceleration SD. At the time of 1.2sec, the Stop Manager begins to catch up again with the
PVT reference, with the SD acceleration.
At the time of approximately 1.7sec, the PVT reference nears the limit of VL[3]=-5000.
Before the reference waveform actually reaches –5000, the Stop Manager finds that speed is
too large for stopping at VL[3] with the deceleration of SD. It therefore reduces the speed,
coming to a complete stop at VL[3] with very small or no overshoot.
At 2.75sec, approximately, the Stop Manager finds that although the position reference is
not yet in range, it will in short time be in. The Stop-Manager begins to accelerate the motor
into the permitted range, so that catching up when the reference returns to range will be
immediate, without the delay of acceleration.