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Chapter 6 Programming Motion • 92 USER MANUAL
are moving back and forth. For example, when operating with servo motors, the trippoint AM (After
Motion) is used to determine when the motion profiler is complete and is prepared to execute a new
motion command. However when operating in stepper mode, the controller may still be generating
step pulses when the motion profiler is complete. This is caused by the stepper motor smoothing filter,
KS. To understand this, consider the steps the controller executes to generate step pulses:
First, the controller generates a motion profile in accordance with the motion commands.
Second, the profiler generates pulses as prescribed by the motion profile. The pulses that are generated
by the motion profiler can be monitored by the command, RP (Reference Position). RP gives the
absolute value of the position as determined by the motion profiler. The command, DP, can be used to
set the value of the reference position. For example, DP 0, defines the reference position of the X axis
to be zero.
Third, the output of the motion profiler is filtered by the stepper smoothing filter. This filter adds a
delay in the output of the stepper motor pulses. The amount of delay depends on the parameter which
is specified by the command, KS. As mentioned earlier, there will always be some amount of stepper
motor smoothing. The default value for KS is 2 which corresponds to a time constant of 6 sample
periods.
Fourth, the output of the stepper smoothing filter is buffered and is available for input to the stepper
motor driver. The pulses which are generated by the smoothing filter can be monitored by the
command, TD (Tell Dual). TD gives the absolute value of the position as determined by actual output
of the buffer. The command, DP sets the value of the step count register as well as the value of the
reference position. For example, DP 0, defines the reference position of the X axis to be zero.
Motion Profiler
Stepper Smoothing Filter
(Adds a Delay)
Output Buffer
Step Count Register (TD)Reference Position (RP)
Output
(To Stepper Driver)
Motion Complete Trippoint
When used in stepper mode, the MC command will hold up execution of the proceeding commands
until the controller has generated the same number of steps out of the step count register as specified in
the commanded position. The MC trippoint (Motion Complete) is generally more useful than AM
trippoint (After Motion) since the step pulses can be delayed from the commanded position due to
stepper motor smoothing.
Using an Encoder with Stepper Motors
An encoder may be used on a stepper motor to check the actual motor position with the commanded
position. If an encoder is used, it must be connected to the main encoder input. Note: The auxiliary
encoder is not available while operating with stepper motors. The position of the encoder can be
interrogated by using the command, TP. The position value can be defined by using the command,
DE.
Note: Closed loop operation with a stepper motor is not possible.