How It Works; Initialization; Parameter Use; Position Sensing - Delta Computer Systems TMC 188/40 Series Manual

TMC 188/40 Motion Control Module

How It Works

Initialization

When the Motion Control Module is powered up, the SCALE and OFFSET parameters are set to the
default values. The ACTUAL POSITION is then calculated based on the default values. The
REQUESTED POSITION, COMMAND POSITION and TARGET POSITION are set to the calculated
position. The EXTEND LIMIT and RETRACT LIMIT are set to the ACTUAL POSITION. These
values keep a 'G' command from moving the axis until the axis parameters are initialized. This
makes the P/C responsible for setting the EXTEND and RETRACT limits using the 'P' command to
change the VINIT parameters.
After the 'P' command is sent, two additional P/C scans are needed to process the parameters. A
new ACTUAL POSITION is computed and the REQUESTED POSITION, COMMAND POSITION,
and TARGET POSITION are updated with the new ACTUAL POSITION.
Once the VINIT parameters are set, you can move an axis by setting the ACCELERATION and
DECELERATION distance or rate, SPEED, and REQUESTED POSITION to the desired values, then
writing a 'G' in the VWRITE COMMAND field. The TMC 188/40 will move the axis to the new position
using the most recently programmed parameters.

Parameter Use

The VWRITE parameters (MODE, ACCEL, DECEL, SPEED, REQUESTED POSITION, and
COMMAND) can be changed while the axis is moving, and any change will take effect on the next
scan. For each new move, usually only new REQUESTED POSITION and COMMAND parameters
are written.
If an axis halts because of an error, the condition can be cleared by sending a new COMMAND.
Since the last command is stored in the command register, the new command must be different for
the MCM to detect the change. For example, if a move is started with a 'G' command and the move
halts on an error, another 'G' command will not clear the error since it is the same as the command
stored in the COMMAND register. However, if the first 'G' command is followed by an 'N' command
(No-Op), then another 'G' command would clear a HALTED condition, since the MCM would detect
the change from 'N' to 'G'.

Position Sensing

Position sensing is done by sending a TTL-level interrogation pulse to the axis transducer, then
measuring the time between the start and stop pulses returned by the transducer. The polarity of the
interrogation pulse can be set with jumpers P4-P7. The return pulse must be a positive pulse of at
least 1.5 volts. The time resolution is determined by the frequency of the counter crystal (27.75 MHz.
in the TMC 188/40). The actual resolution is determined by the number of interrogation pulses used
for a single position measurement. Each pulse is called a recirculation.
In the TMC 88/40 the number of recirculations can be selected with jumpers P8-P11. Usually four
recirculations are used, giving the best resolution. See page 49 for more information about
recirculation (For Quadrature or Analog options, see the appropriate appendix).

Drive Output

The drive calculated by the TMC 188/40 is sent to a 12-bit digital-to-analog converter (DAC). The
output of the DAC can be configured for either voltage or current mode. Jumpers P12, P13, P14, and
P15 select the mode. Jumpers P16, P17, P18 and P19 select the full scale range (±10 volts,
volts, ±2.5 volts or ±100mA, ±50mA, ±25mA). For best resolution use as much of the output‟s range
Delta Computer Systems, Inc. 360/254-8688
How It Works
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