Servo, kinda

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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?


Re: Servo, kinda
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  

(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.)


Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
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Re: Servo, kinda
On Wed, 11 Jan 2017 20:09:50 -0800, tabbypurr wrote:

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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.

Tim Wescott
Control systems, embedded software and circuit design
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Re: Servo, kinda
On Thursday, 12 January 2017 06:29:37 UTC, Tim Wescott  wrote:
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Just what I needed to know, thank you.


Re: Servo, kinda
On 12/01/2017 04:09, wrote:
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Parking switch? Very common on windscreen wiper motors!

Mike Perkins
Video Solutions Ltd
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Re: Servo, kinda
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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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