Use optical home sensors; do not use micro switches. High rotational speeds and constant wear will kill microswitches, no matter how well you mount them.

Animated diagram shows slot and flag type home sensor mounting. Triangle indicates home sensor position. 'E' circle turns green when the software detects the homing edge of the slot (or flag), empty circle turns green when home sensor is not being blocked by the slot mask or flag.

Attach a disk with a slot cut into it on or as close to the motor shaft as possible, to avoid linkage slop from affecting homing. The slot does NOT need to be thin; the OPCS software will always home to one edge of the slot, not to the width of the slot, making for highly accurate homing, regardless of slot thickness. Also, if the slot is too thin, the sensor could miss it during rotation.

Mount the sensor to the motor bracket. This way the bracket can be removed with the motor and sensor all as a single assembly.

It is sometimes nice to have an led to give a visual indication when the sensor is in the home position. Some Omron sensors have a light on them already.

Use optical home sensors; do not use micro switches. Besides being solid state, they are simply more accurate.

Home At End Of Track

If the home position is going to be at one extreme end of the track, then mount the sensor to the stationary base, and put a flag on the moving base that interrupts the sensor when it hits the end of the track. This way, the computer always knows which direction to seek the home position.

Home In Center Of Track

Sometimes one wants the home position of a linear track to be in the middle, such as for the lens (focus) board. An obvious problem is having the computer know which end of the track the channel is at, so it knows which direction to run the motors to seek the home position. This means a simple flag isn't sufficient.

In this case, it's best to mount the sensor to the moving base, and mount a bar of steel that is half the length of the track to the stationary base, such that one end of the bar is flush with one end of the track, and interrupts the sensor for that entire half of the track.

Animated diagram shows how to mount a home sensor on a linear axis, where home is at the center of travel. Gray bar of metal is mounted to bed, running half it's length. Right edge of bar is the 'homing edge'. Sensor (triangle) is blocked by bar during half the travel of bed, which software uses to determine which direction to move bed to find home. While bed moves, software monitors the sensor (S) until it changes state, detecting homing edge (E).

This way, the computer knows which end of the track the channel is sitting just by looking at whether the home sensor is triggered or not. The computer can then know which direction to run the motor to seek home. Then it just runs the motor until the sensor changes state, which will always be at the home position.

The software is normally configured to approach home from only one direction, preventing mechanical slop from affecting homing accuracy.

Trip Switches

Dead Man Switches, Emergency End Of Track Switches.. what ever you call them, the OPCS software supports trip switches to stop all motors if any one of the axes is about to run off the track. Triggering a trip switch is the equivalent of hitting the ALLSTOP key.

Use trip switches protect your linear axes. Should the operator accidentally tell a channel to run off the end of the track, the trip switches will prevent crashing the hardware.

Since trip switches are rarely activated, it is okay to use mechanical switches, but you should probably use optical sensors instead.

Wire all trip switches in series. This way interrupting any one triggers a single bit on the computer. Then configure the tripswitch command in the opcsdefs.opc file to monitor this bit. Tripping any switch will have the same effect as hitting the ALLSTOP key.

Put trip switches at either end of each linear channel, and mount them to allow for at least some amount of overrun, since stopping motors involves slight overtravel just to ramp the motors down to a stop.

It is recommended you use localized LEDs at each trip switch, to indicate which trip switch is the cause of the problem.

Prevent Noise!

Needless to say, be sure your wiring is extra-resistant to electronic noise, since the entire run of a series rigging basically comes down to an extremely long run of wire. Refer to the tripswitch OPCS command's documentation for more info.

Braiding Motor Wires

You will most likely want to braid the wires that come off the motors. If you don't have a 12 year old daughter handy, or simply keep forgetting, then use this wire braiding reference.

Superior Electric Motors - Models/Sizes
Superior MO61 MO62 MO63
Superior MO91 MO92 MO93

Please note: OPCS does not sell motors.
Customers must purchase motors from motion control distributors or motor manufacturers; see the links page.

Superior Electric Stepper Motors Wire color diagram for 4-Wire / 6-Wire / 8-Wire Motors

This diagram of Superior Electric 4/6/8 wire motors is excerpted from the Superior Electric "Slo-Syn 440-EP110 Stepper Motor Indexer/Drive product manual.

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© Copyright 1997, Greg Ercolano. All rights reserved. To report documentation errors, send email to