Laser Printer Motors
Laser printers break, are retired and normally sent through some recycling process within an institution. One of the ways to build up a set of motors for engineering projects is to take the laser printers apart. There are usually two motors in them. One moves paper through the printer and the other spins the mirror the laser bounces off of. The goal here is to document the motors found. The information comes from information found in printer manuals.
Paper Path Motor
Laser printers have a single motor that causes all movement in a printer except the spinning mirror that the laser bounces off of. These motors cost around $60 if purchased. It appears that the circuitry underneath is designed to keep them running at a constant speed even if the load varies by drawing more current.
The printer path motor is typically an outboard, brushless DC motor. A bunch of gears are attached to it that cause all movement within the printer. The cable going to it connects to a controller as follows:
The cable has a J301 connector on one end and a J52 connector on the other end. There are 7 wires going between the connectors. From the motor's perspective:
- pin 1&2 ground
- pin 3 MON .. main motor rotates when "L" .. into the motor .. probably ground
- pin 4&5 24 volts dc power to the motor
- pin 6 MRDY .. motor rotating normally .. out of the motor to controller
- pint 7 HALF ... rotate half speed when "L" .. into the motor .. probably ground
The next figure gives us more detail:
Again, from the motor's perspective:
- pin 1&2 ground .. nothing new
- pin 3 .. transistor is used to pull the motor to ground .. indicating that IC501 in the controller can not sink the current from the motor .. means that need to protect the arduino from spikes, back EMF, etc from the motor on this pin .. in different printer manual this is pulled up to 5 volts through pull up resistor like pin 6
- pin 4&5 24 volts .. nothing new
- pin 6 is tied high to 3.3 volts through a pull up resistor, so the motor is probably not drawing too much current when it pulls this low to indicate normal operation .. in different manual 3.3 volts is replaced with 5 volts
- pin 7 is also tied high to 3.3 volts through a pull up resistor .. different from pin 3 .. this has something to do with the circuit board the brushless outboard DC motor is mounted on .. in a different manual this is 3.2 volts
First look at the solder pads of the cable connection to the circuit board underneath the motor to figure out where pin 1 is. Can see pins 1 and 2 (ground) are soldered together. Pin 3 is isolated as it should be. Pins 4 and 5 are soldered together (24 volts). Pins 6 and 7 are isolated as they should be.
Next found a connector from the printer and re-attach the cables to the motor. Then strip the ends of the wires and "tin" them with a soldering iron like "tin" the tip of the soldering iron. Then solder the stranded cable to solid cable that can be stuck into the arduino headers. Then warp electricians tape around the soldered joints in case they accidentally touch each other.
Now the goal is to match the colors up with the pins.
- red is ground (pins 1 and 2)
- blue is Motor on .. touch to ground when want to spin (pin 3)
- orange is 24 volts (pins 4 and 5)
- brown is what want to hook to a scope to see what the output of the motor looks like (pin 6)
- green is touched to ground to cut the speed in half (pin 7)
The next step is to mount the motor on a board so it is easier to hold onto when it starts to spin.
Hooked up and motor spun fast and then slow. Drawing 120 ma fast, 85 ma slow and 50ma while off. Can not tell the speed.
Applying a load causes it to draw up to 1A .. max of the supply using. Looks like it is maintaining constant speed while different loads are applied.
Hook the brown wire to the middle of a voltage divider (probably a pot) and tie to an oscilloscope to see what happens. Perhaps can get an output that varies with the hall effect probes in the brushless motor.
Then hook to an arduino and use it to turn the motor off and on and display speed/rpm.
Then perhaps start hacking the circuitry on the circuit board to see if the speed can be varied .. either manually or electronically.