Hello,
I have a gearbox on the end of an electrical motor that is used to drive a chain/belt system in a manufacturing environment. On the gearbox, there is a small plastic gear with a slotted hole in it, that is used to spin a cable going to a mechanical gauge to measure gearbox speed. We vary the voltage on the motor to keep the gearbox speed at a set point, as the load on the system changes daily and the speed with it.
The cable wears out from time to time because of the poor angle. More often than the plastic gear that's spinning it. It gets a kink in it somewhere and then breaks and starts to fray.
I want to do away with the cable. Is there a type of sensor that I can mount on the gearbox facing the outlet where the cable goes in, and then machine an adapter to spin the sensor so I can output an RPM reading to an LCD screen?
Someone mentioned mounting a small servo motor to the gear, and having the gearbox spin the servo and then just measure the speed of the servo. I'm not sure it works that way. Is there a type of sensor I can mount directly to it, spin it, and use a library or example for simple speed measurement? I'm trying to avoid magnetic pickups, hall effect sensors, etc, because the speed gear itself is plastic, and a metal version is not available.
There are lots of optical sensors (often called photointerrupters) made to detect slots in wheels. Is there room to fit one in?
a small plastic gear with a slotted hole in it
Can you position a optical interrupter photo sensor to read through the slot?
I'm trying to avoid magnetic pickups, hall effect sensors, etc, because the speed gear itself is plastic, and a metal version is not available.
Can you attach a magnet to the side of the gear?
mounting a small servo motor to the gear, and having the gearbox spin the servo
A rotary encoder turned by the gear.
All good answers, but in the mean time, how often do you lubricate the cable?
Paul
The cable is in a nylon tube so nothing comes in contact with the cable itself.
The cable is at roughly a 180 degree angle because the output gear is facing towards the ground.
Its a relatively small project. Savings is roughly $1200/year after the cost of the components for the digital gauge, but if it works, I'll get buy-in on much larger projects I would like to do.
The face of the gear that the cable slides into is flat. There are no spokes, and you cannot see the teeth of the gear. An optical sensor isn't an option in this case. I need something to physically spin.
The face of the gear that the cable slides into is flat.
Can you provide a drawing or photograph of the mechanical arrangement. I don't understand about the cable sliding into the gear.
What access to you have to the gear? Can you take speed of the main driven chain or belt?
The face of the gear it flat and smooth. You can't even tell its a gear there from the outside. It has a hole in it the gear face that the cable slides into, and the hole is flat, like a flathead screwdriver notch, but its about an inch deep. The ends of the cable are flat, look similar to a flathead screwdriver, and slide into these holes. The nylon covering over the cable has ends on it that are threaded, and they thread onto the body of the gauge and gearbox to secure the cable. The gear spins, the flat end of the cable is secured into the middle of the gear.
The face of the gear that shows through the housing for the cable to slide into is roughly 2" wide.
They DO offer an electrical connector for this gear. It attaches to the gearbox and slides into the face of the gear just like the cable does. You can them in 4, 8, 16 pulse per rotation versions. This would seem like a no-brainer to use, but they're $3500 for the sensor with wiring and digital readout, or roughly the cost of 3 years worth of the cables for the current configuration.
If I could get a motor, sensor, etc that outputs X pulses per rotation, I could make up a bracket and adapter to mount it to the gearbox and attach to the slot in the gear, and save a LOT of money.
JoeNova:
The cable is in a nylon tube so nothing comes in contact with the cable itself.
The cable is at roughly a 180 degree angle because the output gear is facing towards the ground.
Its a relatively small project. Savings is roughly $1200/year after the cost of the components for the digital gauge, but if it works, I'll get buy-in on much larger projects I would like to do.
The face of the gear that the cable slides into is flat. There are no spokes, and you cannot see the teeth of the gear. An optical sensor isn't an option in this case. I need something to physically spin.
I am guessing, but if wear is involved, something is touching something. Anyway, how fast is the gear revolving? Is the gear clean enough to glue a bit of reflective tape to it? Then an IR LED could light the reflector and a sensor could pick up the light and signal an Arduino that the gear made one revolution.
Paul
We usually spin the gearbox at 4000 RPM, but it gets as high as 10000 on small-load production runs.
We usually spin the gearbox at 4000 RPM, but it gets as high as 10000 on small-load production runs.
Is that the speed that the plastic gear is rotating?
You should be able to create an axial interface between the gear slot and the shaft of a high speed encoder. You want to find something rated for the 10000 rpm. The pulse per revolution is not really relevant, as you will likely use the index pulse, for one pulse per revolution. Be sure you get an encoder with an index pulse.
There are many options, and one possibilty would be the Bourns EMS22D or EMS22Q series. They look to be less than $50 US at Mouser.
If you can get a marker on the gear face you could pick it up with a non contact reflective optical sensor(possibly commercially available integrated with a tachometer) for a lower cost, but it would be more affected by dirt in an industrial environment.
JoeNova:
We usually spin the gearbox at 4000 RPM, but it gets as high as 10000 on small-load production runs.
I know this is late, but I have been gone. At the speeds you listed, it's no wonder the cable is wearing out. What speeds is the cable rated for? A non-contact sensor is certainly needed.
Paul