Motion Control

Comment

Comment by lees on December 3, 2009 at 8:47pm

Capacitive sensors give very high performance. Unfortunately, they require a driver system and generally some tuning. Optical reflective sensors can require a bit of dong to make work well for a gear, but they are very cheap, come in a number of packages/voltages/logic rules, and do very well if they are able to be kept clean. Some models can discriminate distance surprisingly well, and this means even smaller teeth can work.

Comment by James Jones on November 6, 2009 at 4:33am

To state my objective more plainly: does anyone in this community have an opinion as to the difficulty or feasability of designing a linear motor that can be built using a coil winder and a small, light CNC mill? TIA, James

Comment by lees on October 22, 2009 at 2:03pm

An often overlooked encoder for some low to moderate speed applications is the optical mouse chip. It can work with performance similar to a 1024 cpi linear encoder, can provide feedback for multiple axes (the output is a vector rather than a simple quadrature or count/speed), and is relatively easy to implement. Surface characteristics are important but can be very flexible. They tend to get contaminated in dusty environments. They also have trouble with cumulative accuracy and require an independent home system of some sort. It can only handle several inches per second well. But the shortcomings can often be addressed for a variety of applications. A $3 to $7 chip with built-in serial capabilities that accomplishes what a lot of encoder strips, packaging, and software development would normally do is an attractive option.

Comment by James Jones on October 22, 2009 at 8:39am

Hi, thought I'd barge in and begin asking what will become 10,000 questions!
I have a little project at www.cubespawn.com, that I'm gathering information for all the various aspects of getting the first machine together. My first big goal, however is to find a DIY linear motor design that can be built with fairly primitive machining resources - mainly to simplify the motion control, positioning, and feedback aspects of a bootstrapping light CNC router as shown on the site. As opposed to a conventional ballscrew/stepper solution - any feedback appreciated!

Comment by Bob Setbacken on September 17, 2009 at 8:18am

Hi Suresh,
Control of spindle velocity is probably the most important thing in cutting metal. A smooth finish requires very well controlled spindle speeds. For this reason Steppers are in my experience never used. You need a real servo for this, brush or brushless. Of course if you are shooting for low cost and not trying to reach high levels of precision, a stepper could work, but the limitation on rpm will mean that you will not be able to remove metal very quickly.

Comment by Suresh N on September 16, 2009 at 9:30pm

Hi Bob,
certainly the gears will not be exposed and i am using high precision rotary encoders for positioning. Do you have any experience with small machine tools? I am planning to use stepper motors for powering the spindle.
Regards
Suresh

Comment by Bob Setbacken on September 16, 2009 at 7:48am

Eirc, how clean will the gear be? Is it exposed to the environment? Why do you not want to use magnetic sensors?

Comment by Suresh N on September 16, 2009 at 3:46am

Hi, everybody!
I am designing a high precision high accuracy machining center used for machining small components mostly nonferrous and plastic type. Can anybody suggest the motors and gear assemblies required. This machine tool will be capable of drilling, milling, gear cutting, will have 3 axes linear motion capabilities. I also welcome any sponsorers if interested.
The main idea is to bring in a substitute for injection moulding and other costly tooling.

Regards
Suresh (shuresh74@hotmail.com)

Comment by Eric Fleischer on February 4, 2009 at 12:56pm

I'm currently using a linear-type strip encoder to read the position of a large ring gear, but having problems with the strip. Is anyone familiar with a non-Hall type gear tooth encoder, that can give me relative position by reading the position and passage of aluminum gear teeth?