Quadrature Encoder-Specific Commands - Delta Computer Systems TMC 188/40 Series Manual

TMC 188/40 Motion Control Module

Quadrature Encoder-Specific Commands

The TMC 188/40-(T)Q has two commands which are specific to quadrature encoders:
@ Command
(40H, 64D)
The @ command automatically moves the axis, attempting to find the Home position. The At
Command Position bit must be set and the axis initialized (with a 'P' command) before the TMC
188/40 (T)Q will accept the @ command. When the Home input is active (true), the Actual Position
is set to the value in the Requested Position field.
NOTE: The FEED FORWARD, SPEED, MODE , ACCEL and DECEL parameters must be set to desired
values when the @ command is issued. During the Home routine the axis moves under open
loop control and the drive output is calculated as:
The @ command works as follows:
1) The AT COMMAND POSITION bit is cleared and the axis retracts until one of the following
conditions is met:
A) the Home input is true,
B) the Limit input is false, or
C) the axis is obstructed
2) The axis then extends until the condition clears. If the Home was encountered the axis
reduces drive by half, then repeats Step 1.
3) Steps 1 and 2 repeat until the axis stops exactly on the Home position.
4) When the Home is located, the axis extends 100 quadrature encoder counts from the Home
position, the AT COMMAND POSITION bit is set, and the ACTUAL POSITION is set to the
value in the REQUESTED POSITION field + (100 counts * SCALE).
If a limit or obstruction is encountered, the axis reverses direction.
If the axis is between a limit and an obstruction (i.e. caught between the limit switch and the
physical limit of the system) the axis is moved beyond the limit away from the obstruction.
The Home routine can be terminated at any time with the Z command.
When an @ command is given, the ladder logic program should use a timer to make sure the Home
is found within a reasonable amount of time. If no Home is found the axis will be stopped and the
AT COMMAND POSITION bit will remain cleared.
The Home input causes the counters to be loaded with the Preset Value determined from the last
@ command. If a new SCALE or OFFSET is issued with a P command, an @ command must be
issued to update the Preset Value of the Home input.
If SPEED is set to 0 (zero) and an @ command is issued, then only the hardware counters are
changed; they are loaded with a Preset Value defined by:
Preset Value = (Requested Position - Offset) x SCALE / 1000
rather than the default value of 100. The next time the Home input is active this preset value will be
transfered to the transducer counts value.
Z Command
(5AH, 90D)
Delta Computer Systems, Inc. 360/254-8688
FEED FORWARD x SPEED / 10,000
Appendix C: QSBX/40 Module
87