Servo, kinda

A motor & geartrain moves to a certain position where a switch switches it off. Thus wanted position is reached. But what are such mechanisms called? Servos, or something more basic?

NT

Reply to
tabbypurr
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Simply "limit switch".

The control theory equivalent I suppose would be hysteretic control, except it stops in one cycle without integrating an error and oscillating continuously (monostable, not astable). The error band (how far it overshoots the threshold) will be comparable to the ripple of such a control.

(It would be astable if the switch caused the motor to reverse, rather than stop completely. Then you could imagine sliding the switch around, and having the drive train follow its position.)

Tim

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Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
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Reply to
Tim Williams

Generally if it has a fixed target point it's a regulator, but if you can move the target point around it's a servo. So if there's not a knob or a slider to move the switch, it's not a servo (a means for a maintenance guy to move it doesn't count).

However: people will look at you strangely if you call it a regulator, unless you preface your statement with "in theory...". Just call it a limit switch, as the other Tim has suggested.

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Tim Wescott 
Control systems, embedded software and circuit design 
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Reply to
Tim Wescott

Just what I needed to know, thank you.

NT

Reply to
tabbypurr

Parking switch? Very common on windscreen wiper motors!

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Mike Perkins 
Video Solutions Ltd 
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Reply to
Mike Perkins

quadrature incremental encoder. Absolute gray encoder. optiocal, inductive, magnetic, capacitive or mechanical switch.

potentiometer, inductive linear output senser..

Current load sensing from mechanical stop/Jam.

Windshield wiper motors for the most part normally use a reciprocating connecting rod from an orbital drive, mostly of the wheel type with offset mounting pin. This old style of drive has been around since the dawn of man. The park switch as you call it is simply a switch that opens supply circuit when it is in its park position.

Most wiper units have a Main Supply and the bypass supply to close the internal switch, along with the common/grd of course. The idea of the main supply of course is to allow the unit to have power when you turn off the switch. This will auto retract the wipers the next time you turn on the ignition or acc, if not in the park pos to start with..

With the poster comments, I would think that a mechanical limit switch would serve as the complete cycle stop switch.. If you want to repeat the cycle, you can close that switch. I guess this only holds true if the mechanics are design with a reciprocating motion.

But I really think this video will help much more.

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Jamie

Reply to
M Philbrook

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