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Chapter 3 Connecting Hardware
DMC-1000
Home Switch Input
The Home inputs are designed to provide mechanical reference points for a motion control application.
A transition in the state of a Home input alerts the controller that a particular reference point has been
reached by a moving part in the motion control system. A reference point can be a point in space or an
encoder index pulse.
The Home input detects any transition in the state of the switch and toggles between logic states 0 and
1 at every transition. A transition in the logic state of the Home input will cause the controller to
execute a homing routine specified by the user.
There are three homing routines supported by the DMC-1000: Find Edge (FE), Find Index (FI), and
Standard Home (HM).
The Find Edge routine is initiated by the command sequence: FEX <return>, BGX <return>. The Find
Edge routine will cause the motor to accelerate, then slew at constant speed until a transition is
detected in the logic state of the Home input. The motor will then decelerate to a stop. The
acceleration rate, deceleration rate and slew speed are specified by the user, prior to the movement,
using the commands AC, DC, and SP.
It is recommended that a high deceleration value be used so
the motor will decelerate rapidly after sensing the Home switch.
The Find Index routine is initiated by the command sequence: FIX <return>, BGX <return>. Find
Index will cause the motor to accelerate to the user-defined slew speed (SP) at a rate specified by the
user with the AC command and slew until the controller senses a change in the index pulse signal from
low to high. The motor then decelerates to a stop at the rate previously specified by the user with the
DC command.
Although Find Index is an option for homing, it is not dependent upon a transition in
the logic state of the Home input, but instead is dependent upon a transition in the level of the index
pulse signal.
The Standard Homing routine is initiated by the sequence of commands HMX <return>, BGX
<return>. Standard Homing is a combination of Find Edge and Find Index homing. Initiating the
standard homing routine will cause the motor to slew until a transition is detected in the logic state of
the Home input. The motor will accelerate at the rate specified by the command, AC, up to the slew
speed. After detecting the transition in the logic state on the Home Input, the motor will decelerate to
a stop at the rate specified by the command, DC. After the motor has decelerated to a stop, it switches
direction and approaches the transition point at the speed of 256 counts/sec. When the logic state
changes again, the motor moves forward (in the direction of increasing encoder count) at the same
speed, until the controller senses the index pulse. After detection, it decelerates to a stop and defines
this position as 0. The logic state of the Home input can be interrogated with the command MG
_HMX. This command returns a 0 or 1 if the logic state is low or high, respectively. The state of the
Home input can also be interrogated indirectly with the TS command.
For examples and further information about Homing, see command HM, FI, FE of the Command
Reference and the section entitled ‘Homing’ in the Programming Motion Section of this manual.
Abort Input
The function of the Abort input is to immediately stop the controller upon transition of the logic state.
NOTE:
The response of the abort input is significantly different from the response of an activated
limit switch. When the abort input is activated, the controller stops generating motion commands
immediately, whereas the limit switch response causes the controller to make a decelerated stop.
NOTE:
The effect of an Abort input is dependent on the state of the off-on-error function for each
axis. If the Off-On-Error function is enabled for any given axis, the motor for that axis will be turned
off when the abort signal is generated. This could cause the motor to ‘coast’ to a stop since it is no
longer under servo control. If the Off-On-Error function is disabled, the motor will decelerate to a
stop as fast as mechanically possible and the motor will remain in a servo state.
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