Rotary Encoders

vk6kci

New Member
Hi All,

I am working on a project that regulates a sewing machines stitch length in proportion to the speed that the sewing machine is moved around on a quilting frame.

Has anyone on the forum done this?

For this I need some really simple but reliable rotary encoders for the X,Y direction of the frame that can output pulses around 500PPR or more. PWM output would also be ok, as I intend to interface the encoders to a Picaxe to provide a semi proportional resistive output. (I have that part worked out)

There seems to be plenty of rotary encoders out there, but most are fairly expensive and of the quadrature or multiple grey code type. I just need a simple slotted disk type incremental encoder that doesn't care about direction.... just square wave pulse or PWM output relative to rotation of any voltage but of course around 5V pulses would be good.

I'm sure the vector maths for diagonal velocity shouldn't be too difficult, but any help there would be appreciated as well.

Looking forward to your replies!

Regards
Maarten
VK6KCI
 

BeanieBots

Moderator
Has anyone on the forum done this?
I'll be stunned if you get a yes to that one!

For a basic pulse encoder, pull apart your nearest old 'ball' type mouse.
For the vector maths, X1/X2 support sin/cos.
Otherwise, use a lookup table and extrapolate.
 

vk6kci

New Member
Thanks folks,

There are really two criteria for the PPR. In the first instance, I need enough PPR so that I can get pulses if the sewing machine is pushed in any one direction on the quilting frame with the needle down. (to start sewing) Whilst I don't know what this rate is, I suspect it needs to be reasonably high because there will be latency in the actual sewing machine motor starting and also in execution of the picaxe code which will have to include false start routines.

I have checked and found that I have at least 3-5mm of lateral movement with the needle down because of needle flex and fabric stretch. This should be enough to get pulses started but exactly how many pulses I need to run through false start routines and motor start remains to be seen. I'm thinking 400PPR should be more than enough!

Once the machine has started, the resolution may well be lower as I only need proportional PPR to 10 individual resistance outputs. (the sewing machine foot controller is a 10K variable resistor and I only need a resolution of 1K to have 10 speed steps)

Andrew.. if you have details on how to buid a 440PPR, I can then experiment further to see if it works.

Anyone else....... any ideas most welcome!!

Are there any other ways of measuring velocity of a quilting frame?

Kind regards
Maarten
VK6KCI
 

Andrew Cowan

Senior Member
My robot has this kind of system to let the PICAXE know how fast the motor is going.

It uses slotted optocouplers and striped discs to create a waveform (is about 2V p-p and curvey). This goes into an op amp, which turns it into a 3V p-p digital signal. Ideally I would have used a rail to rail op amp, but that is all I had around.

This then goes into a transistor, which buffers it up to a standard 5V TTL digital signal. The PIC accepts this and works fine.

The stripes on the disc need to be around 0.6mm wide for the system to work (with my slotted optos). 400PPR = 480mm circumference = 15cm diameter wheel.

The larger the wheel, the more stripes you can have. I haven't tested how fast the system works, but my tests at 400PPR were OK. I'm using a 100 PPM setup in my robot.

A
 

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