[biederboat]

Hey guys, I'm pretty much a "newbie" to PC controlled motion; my expertise is more with PLC's. My basic question is this: will a SmoothStepper system, properly programmed and with proper hardware, do what we want it to. We are trying to re-purpose a measuring scope with under the following circumstances:

1. Two-axis motion control that is primarily used to "get to an approximate area" either through a program or manual use of a joystick.
2. Once you're at an area, the motors need to be moved "manually" (with hand-cranks). The stepper motors would have to turn independently of their resolution (i.e go between pulses). So, is that even possible? Would the motors have to be turned off or somehow decoupled?
3. Once you're done looking at an area you'd like to hit a "go" button and tell the system to move to the next position where you would do additional manual moves.
4. For "one-time" (e.g. prototype) parts, we'd like to use a joystick to control the motors and travel around the part.

The main point here is that stepper motors just don't have the resolution for the details in our parts; they would be fine to get to an area but then you'd have to move manually. The current system does have hand-cranks on the back of the motors but the rest of the system is so old and unsupported we want to chuck it and add new motors & control system. Hopefully I've clarified that correctly.

Thanks for any feedback,
BB

[awerby]

1. Two-axis motion control that is primarily used to "get to an approximate area" either through a program or manual use of a joystick.
2. Once you're at an area, the motors need to be moved "manually" (with hand-cranks). The stepper motors would have to turn independently of their resolution (i.e go between pulses). So, is that even possible? Would the motors have to be turned off or somehow decoupled?

[When the motors are powered up but stationary, you can't crank the cranks and move them. That's when steppers have their maximum torque.]

3. Once you're done looking at an area you'd like to hit a "go" button and tell the system to move to the next position where you would do additional manual moves.

[What sort of manual moves did you want to do? What makes you think that would be more accurate than simply commanding the moves in software?]

4. For "one-time" (e.g. prototype) parts, we'd like to use a joystick to control the motors and travel around the part.

[You can do that, but it works just the opposite of how you seem to think it does. You can use manual jogging to get most of the way there, but for fine control you'd want to use the stepper drivers and software.]

The main point here is that stepper motors just don't have the resolution for the details in our parts; they would be fine to get to an area but then you'd have to move manually.

[I have a hard time believing that. What sort of resolution are you talking about?]

The current system does have hand-cranks on the back of the motors but the rest of the system is so old and unsupported we want to chuck it and add new motors & control system. Hopefully I've clarified that correctly.


Thanks for any feedback,
BB

[You've clarified it some, but it's still pretty turgid. This idea of intermittent motor-controlled and manual movement doesn't make any sense to me. For one thing, if fine control is what you want, stepper motors do a much better job than hand-cranks. I've used both kinds of machines, and it's invariably more accurate to use an MDI (manual Data Input) command to get to a given position than to try and achieve the same thing with hand-cranks. When cranking, one often overshoots the mark and then has to backtrack a few thousandths, whereas the motors just go there and stop. If you're worried that your steppers, which typically have 200 discrete steps per revolution (and the intermediate half-steps can be hit pretty accurately), still aren't going to hit the spot, then consider adding a timing belt and pulleys to expand that to 1000 steps per rev (with a 5/1 ratio) or more if you need it.

The Smoothstepper will help if you're trying to use a computer without a parallel port, or need higher throughput, but it's not going to increase the accuracy of the system.]

Andrew Werby
301 Moved Permanently

[biederboat]

I was trying to keep the explanation straightforward but the measuring we need to do is down at the micrometer level and a stepper would never hit that. The gear reduction on the drive after the motor is fine enough that with the existing crank (inline with the motor shaft) you can easily move around without over/under shooting. Hopefully I'm wrong, but I just can see it being either economical on either a time or money basis to integrate the linear scales for the measuring system. (that are entirely separate from the drive system) into the motion control system. As it stands, I either need to keep the existing digital display and send it's data into the PC via RS-232 (entirely separate project) or integrate the scales directly into the PC but I just don't know if it will buy us anything trying to integrate the scales into the motion control system. For one thing, to do any automated measuring we would need a camera and the payback would likely not be worth it. It's beyond my expertise to do all that but I'm not afraid of tackling a relatively simple 2-axis motion system.

Hopefully that makes it less turgid (had to look that one up!).

BB

[awerby]

In that case, you probably should integrate a MPG (Manual Pulse Generator) pendant into your system. It's essentially a knob you can turn that will move your axes a little at a time. That way you could keep the machine under stepper control, but dial in the final position by hand. Here's one that gets good reviews: vistaCNC