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Question about a motor from a printer

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Daniel Kalseth

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Hi!
I have a couple of motors i got from a printer and i don't understand what the top black cap is there for. Is it to measure speed or what?
This is the motor itself:

Motor
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I am thinking of making a CNC machine and therefor i am also wondering if i need any motor controllers/drivers to spin it both ways?

Thanks in advance!
 

betwixt

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If it's a stepper motor it is probably just a cover over the connections to the coils. If it isn't a stepper, it might cover an optical encoder. In most printers the motors are steppers these days, it's easier to move the motor in known steps than spin it and try to stop it at the right time.

Brian.
 

Daniel Kalseth

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It is a cover to an optical encoder, but how would you connect power to it then? Wouldn't it just be one to each of the coils? (red and blue)? If so, could i connect dc directly or do i need a motor driver/cont

What does the optical encoder do?
 

FvM

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First point is to find out if it's a permanent magnet DC (PMDC) motor, or something different. I agree with your guess that red/blue may be PMDC terminals. You can connect a volt meter and turn the shaft. If yout get a DC voltage changing with direction, it's probably a PMDC.
 

Daniel Kalseth

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What is the optical encoder used for then?

- - - Updated - - -

Yeah FvM, when i connected my volt meter and turned the shaft i got voltage. So it is a PMDC, does that mean i can connect it directly to dc power(i have a bench power supply)
 

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An optical encoder will be a transparent disk with a pattern of radial lines around it's edge. I will sit within one or two optocouplers so the lines interrupt the light beam as they pass in the optocoupler slot. The idea is that as the motor rotates, it turns the disc and produces pulses from the optocoupler at maybe 1 per degree. The driver software counts the pulses to know how many degrees the motor has turned. Typically the software will adjust the power to the motor according to how many rotations it has to make and will follow an acelleration/decelleration profile to prevent it overshooting.

Brian.
 

Daniel Kalseth

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Ahhhh.. I pulled them out from a Lexmark printer and i am going to use a computer to control them. How would i do it and can i use DC directly to the motor to test it or do i need something in-between?
 

betwixt

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Again, it depends on the motor type. One with an optical encoder is just a plain DC motor and applying a voltage will make it rotate, reversing the voltage will make it rotate in reverse. A stepper motor will not turn though, instead of rotating it's own magnetic field to keep it turning, a stepper relies on you doing it electrically by connecting the voltage to one or more coils in a particular sequence. The coils 'pull' the rotor back or forth until they align internally and a sucession of coil windings allow you to then move it on to the next position when they are in turn energized. It allows the motor to be moved by a particular angle, that is why they are generally used in printers where the alignment of carriage and ink is so critical. To make them rotate you sequence the power supplied to the coils so it steps rapidly, giving the appearance of constant motion.

You have 6 wires to the motor, they could be one common connection and five coil conections or you could have three independant coils, if you measure the resistance between wire pairs it will give a clue as to the motor type.

Brian.
 

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