[RLMTS]

Hi,

I would appreciate your feedback / comments on which way you would approach the design task for this simple application, which is fairly cost critical.

The requirements are generally as follows.....

A rotary axis is required to rotate and position a part for plasma spraying (the spraying is accomplished by a robot)

The parts are cylindrically symetrical (if there is such a phrase!) such that there is no weight that could be trying to offset the axis, and there are no other external forces being applied to that axis. So holding whilst in position requires little torque.

Max rotary axis speed = 200 RPM (perhaps via gearbox?)
Motor rating Approx 0.5Kw (Max)

The axis control needs to have a very simple interface with an existing controller (a robot), the existing controller will signal via a digital (on/off) signal to start rotating the axis to it's first position.

Then, after the existing controller (robot) has done the first part of it's spray job it will signal to rotate to the second position,
and so on... perhaps 4 or 5 steps max.

The customer is asking that only ONE output from the existing controller is used to step through the positions.

(1st pulse = move to first pos, 2nd pulse = move to 2nd pos etc)

The new axis control will need to signal back to the robot (via one digital on/off signal) that it has done it's step.

This is quite 'loose' synchronisation, but this is what they are asking for (it's not 'high volume' production, engineers run the kit)

EG:
1st on/off pulse from robot controller = start... go to position 1
Echo back 'DONE' from positioner when axis move to position is complete.
2nd on/off pulse = continue to position 2
Echo back 'DONE' when move is complete.
3rd on/off pulse = continue to position 3
Echo back 'DONE' when move is complete.
etc.

A seperate input to the axis controller from the robot can be used to END the program and return the axis to it's datum or zero position.

The ability to store up to 5 programs each with a max of 5 steps.
(each prog may have more or less steps, different positions etc.)
(one of the programs will be a continuous rotation program until the 2nd step pulse is received or END input is received)

The above control I/face example is not 'set in stone' so alternative signalling/interfacing is possible.

Also the ability to ensure the axis is only allowed to travel in one direction (parameter?) This is because of mechanical issues (chain drive, has slack idling tensioner side of chain! Although this mechanical constraint may be resolved) (Part of the mechanics for this axis exists, but no drive)

The customer will need edit access for adding or modifying the very simple programs / steps / positions.

Can you suggest something that will achieve this at reasonable cost.

NOTE: the accuracy required is quite low! (+-/ a couple degs)
The positioning job is for presenting faces of product (or round bar) to a robotic spray arm, it is not for machining purposes.

I am more familier with the likes of Fanuc 0_C and Siemens Sys 8/810/840 etc but feel this is a costly overkill! Althoug the Siem 802s is tempting (stepper) but still fairly expensive for the application in mind?

Your Comments appreciated..........

Rich.

[Laser.Tech]

Sounds like a job for a small microcontroller connected to either a stepper/driver or servo/driver. Perhaps a BASIC stamp or similiar product? A task this simple, I think even a single PIC chip could handle...

Laser.Tech

[RLMTS]

Thanks Laser.Tech
Mmm... ? Don't think I am into PIC chip programming?
More of an 'off the shelf' guy I suppose!
I'm ok with PLC and CNC programming...

[keebler303]

Definately the cheapest route would be a PIC with a bootloader for uploading modified programs. A small plc would be fine for this. It would make it pretty easy to modify the programs as well. If you can program a plc, just have the plc output a set number of pulses to a stepper or servo drive each time the input is pulsed. Then just bring an output high to tell the robot it is there. You could have a limit type switch which would serve as home, which the plc could home to on power up.

Program

powerup

turn slowly until home input goes high
wait for index input from robot
when received output 72 pulses (steps) on step output
after 72 steps, pulse done output to robot.
go to wait

The number of pulses could be changed to divide the circle evenly into however many parts you wanted. I would use a servo motor and drive capable of step and direction input to interface with a budget PLC.

Matt

[slp_prlzys]

If you chose to go the pic way, this might be right up your alley.
http://cq.cx/ladder.pl

[Laser.Tech]

I would agree, a PIC would be an ideal cheapest solution. However, if you don't feel comfortable learning to program/use one, consider using a BASIC oriented controller. There are several different choices available, most for less than $200. The STAMP and related products come to mind first, All you need is a power supply and serial cable to program from a pc. The program could probably be written in 15 minutes.

p.s. Yes I know BASIC is ANCIENT, but it is sooooo easy, especially for something simple like this...

Laser.Tech

[RLMTS]

Thanks Matt, Laser.Tech & SLP....

I will do some further research based on your comments and bear it all in mind if a job like this ever crops up again. This one was cancelled by customer, purse strings pulled very very tight!

ATB Rich