Digital Read Out for Circumference

[ddmunroe]

Hi,
Do DRO's kits come out for circumference, EG Fitting one to a rotary table !
Displaying degree / minute increments.
If not how could we come up with a device that could read and convert rotational movement to degree display. :thinking::thinking:
I know you like a challenge )
dd

 

[xalky]

A servo motor, which has positional feedback built in, essentialy does that exact thing. Stepper motors do not have this feedback feature, but it does count steps, as long as the steps are not lost, you can essentially do the same thing. The position of the sensor would have to be extrapolated into degrees of rotation for a given diameter of the "scale" ring. This is why this type of thing is easier to do on a CNC machine.

There's not a whole lot of room on a rotary table to mount a sensor ring. Perhaps a magnetic tape that gets stuck to the rotary OD could be used but then there's the whole problem of sensor extrapolation math, which needs to be done in software. Not an easy problem to solve for different diameter and brands of rotary tables. The sensor would almost have to be mounted inside the rotary table or a relief pocket would have to be milled/turned into the bottom of the rotary table to make room for the rotary sensor.

There might already be a product out there for this. I'll bet it aint cheap.

Marcel

Edit: http://www.beisensors.com/optical-rotary-encoders.html

http://www.bei-industrial-products.com/e_rotary_digital-display.html

Here you go. Some examples.

 

[ddmunroe]

A servo motor, which has positional feedback built in, essentialy does that exact thing. Stepper motors do not have this feedback feature, but it does count steps, as long as the steps are not lost, you can essentially do the same thing. The position of the sensor would have to be extrapolated into degrees of rotation for a given diameter of the "scale" ring. This is why this type of thing is easier to do on a CNC machine.

There's not a whole lot of room on a rotary table to mount a sensor ring. Perhaps a magnetic tape that gets stuck to the rotary OD could be used but then there's the whole problem of sensor extrapolation math, which needs to be done in software. Not an easy problem to solve for different diameter and brands of rotary tables. The sensor would almost have to be mounted inside the rotary table or a relief pocket would have to be milled/turned into the bottom of the rotary table to make room for the rotary sensor.

There might already be a product out there for this. I'll bet it aint cheap.

Marcel

Yes mounted internally safe from destruction is what I was thinking. Extrapolating now might be another story, how is it done from a stepper motor ? or is there another device ... a degree reader, position sensor, some thing that might have a more simple interface.
Might even be able to do away with purchasing a simple dividing head if this feature was accurate !
dd

 

[xalky]

Yes mounted internally safe from destruction is what I was thinking. Extrapolating now might be another story, how is it done from a stepper motor ? or is there another device ... a degree reader, position sensor, some thing that might have a more simple interface.
Might even be able to do away with purchasing a simple dividing head if this feature was accurate !
dd

It can't be done from a stepper motor directly, the stepper motor has to be driven by software. The software counts the steps and interpolates the amount of steps and translates it into degrees of rotation. There's no feedback loop. Servos do have a feedback loop however, but Ive never taken one apart to see how it's set-up.

I posted some links to commercially available stuff. There might be more cheaper solutions out there, but that should give you something to chew on.

 

[JimDawson]

Renishaw makes these, but probably not cheap.

There are a few other ways to do this with a rotary table. Installing an external or internal optical encoder would be a good option, as would a Hall effect sensor. I am going to build a powered rotary table for my mill one of these days, but I haven't yet thought about the best (and reasonably low cost) way to do this. Building something inside the rotary table would be the best option, just to protect the hardware. I would want a readout that will give decimal degrees with a resolution to at least 5 decimal places.

If you could insure 0 backlash, you could read the motor shaft position via encoder or stepper.

 

[SEK_22Hornet]

A rotary encoder certainly could be added to a rotary table to read out the rotation information. It would have to count pulses and software would be needed to convert the pulse count into degrees of rotation. Resolution would be limited by the number of pulses per rotation and the gear ratio of the worm drive. Being digital, there would be no way to display a position that was between counts. What you are looking for is a device like the mini lathe DRO systems use ( http://www.littlemachineshop.com/products/product_view.php?ProductID=2222&category= ). It is a self contained rotary encoder and readout for the cross slide of the mini lathes. Unfortunately, that device is a single purpose device that won't work as it is. Adding a rotary encoder to the control shaft would be about the same level of difficulty as adding a stepper motor. It would probably be easier to add a stepper to the table and then build a small control box that set the actual position. Accuracy would depend on the number of steps of the stepper motor. The stepper would add the advantage of micro stepping to increase resolution. The software to control it would be an ideal project for a PIC processor or Arduino board. You could use a small rotary encoder to input the step and direction or you could use a keypad and simply key in the number of degrees of rotation and direction. You would need a display to tell you where you are at. In either case. Both methods would be relative and would require a way to set the zero point. Encoders are available very cheaply, but you do get what you pay for in terms of quality and durability, so an industrial grade encoder would cost just about as much as a stepper motor. Any PIC or Arduino programmers reading this thread?

 

[hvontres]

If you can stomach the sticker shock, Renishaw has some very nice high resolution Angular encoders:

http://www.renishaw.com/en/magnetic-linear-encoders-and-magnetic-ring-encoders--9802

http://www.renishaw.com/en/optical-rotary-angle-encoders--6434

http://www.renishaw.com/en/resolute...te-optical-rotary-angle-encoder-system--10852

These are essentially linear encoders wrapped around a steel ring. (Actualy, the early prototypes I got to play with were exactly that )

As for reading an encoder, you will need a way to count the encoder transitions and convert them to degrees, probably with some type of micro-controller. Ti's Tiva-C boards have support for two encoder channels built in. you can probably also find some low speed solutions for ardunos.

 

[ddmunroe]

If you can stomach the sticker shock, Renishaw has some very nice high resolution Angular encoders:

http://www.renishaw.com/en/magnetic-linear-encoders-and-magnetic-ring-encoders--9802

http://www.renishaw.com/en/optical-rotary-angle-encoders--6434

http://www.renishaw.com/en/resolute...te-optical-rotary-angle-encoder-system--10852

These are essentially linear encoders wrapped around a steel ring. (Actualy, the early prototypes I got to play with were exactly that )

As for reading an encoder, you will need a way to count the encoder transitions and convert them to degrees, probably with some type of micro-controller. Ti's Tiva-C boards have support for two encoder channels built in. you can probably also find some low speed solutions for ardunos.

These units are high quality and they would be the best to use but you still have to develop the degree interpretation into display.
Hmmm this is not such an easy one to figure.
Thank's for posting .... good stuff. Fairly involved if you want to pursue it to finished product. Seems nothing on the market as far as digital readout degree display for rotary tables
dd
[video=youtube;6r2ZThBgSOc]https://www.youtube.com/watch?v=6r2ZThBgSOc[/video]
More on encoders (How they work)
[video=youtube;Q9d3d-gNii8]https://www.youtube.com/watch?v=Q9d3d-gNii8[/video]