High-Speed Input and
Pulse Output Features
3–31
High-Speed Input and Pulse Output Features
Trapezoidal Profile Operation
The trapezoidal profile is best suited for simple point-to-point moves, when the target
position is known in advance. Starting velocities must be within the range of 40 pps to
1k pps. The remainder of the profile parameters are in the profile parameter table.
Trapezoidal Profile
Time
Accel Decel
Velocity
Start position
Target position
Target Velocity
Starting
Velocity
Start
Profile
Complete
Y0
SP104
The time line of signal traces below the profile indicates the order of events.
The HSIO uses logical output Y0 as the Start input to the HSIO, which starts the
profile. Immediately the HSIO turns off the Profile Complete signal (SP104), so the
ladder program can monitor the progress of the move. Typically a ladder program
will monitor this bit so it knows when to initiate the next profile move.
If you are familiar with motion control, you’ll notice that we do not have to specify the
direction of the move. The HSIO function examines the target position relative to the
current position, and automatically outputs the correct direction information to the
motor drive.
Notice that the motion accelerates immediately to the starting velocity. This segment
is useful in stepper systems so we can jump past low speed areas when low-torque
problems or a resonant point in the motor might cause a stall. (When a stepper motor
stalls, we have lost the position of the load in open-loop positioning systems).
However, is is preferable not to make the starting velocity too large, because the
stepper motor will also “slip” some pulses due to the inertia of the system.
When you need to change the current position value, use logical Y1 output coil to
load a new value into the HSIO counter. If the ladder program loads a new value in
CT76/CT77 (V1076/V1077), then energizing Y1 will copy that value into the HSIO
circuit counter. This must occur before the profile begins, because the HSIO ignores
Y1 during motion.
Trapezoidal Profile
Applications
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