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4th axis setup
« on: June 19, 2008, 03:11:14 PM »
Hi All

I am running a wabeco 1210 and I am currently trying to add a 4th axis.

I have used an Arceuro 4"" rotary table and stepper and connected up

using an oldham coupling arrangement.

Problems.

1) The stepper is moving very slowly compared to the other axis

2) I have a loss of accuracy. eg when I tell it to rotate 10 deg it will rotate approx 9.5 deg

(measured using the scale on the table)

I have gone through the full coupling and there is no signs of slippage or backlash

(when power is disconnected the movement turns easily)

My motor settings are as follows

                steps per            vel               acc                 g

x axis          1000               1500             192             0.019579

y axis          1000               1500             190.8           0.19464

z axis          1000               888               89.77           0.0091548

a axis          400                3592.8           689.06         0.070267

Kernal speed 25000

I have tried to up the vel/acc with only marginal improvement

My logic for the 400 steps per is as follows

rotary table ratio 1:72
system uses geckodrives G201 with 10 micro steps
motor step angle 1.8 deg =200 steps per rev

mach steps per rev = 200 x 10 microsteps = 2000

steps per = 2000 x 72 / 360 = 400


Can anyone help ?

Cheers George
« Last Edit: June 19, 2008, 03:41:09 PM by BIGWING »

Offline Chip

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Re: 4th axis setup
« Reply #1 on: June 19, 2008, 07:39:18 PM »
Hi, George

Your 72 to 1 may not be an accurate/exact number , If its moving 9.5 deg with 400 steps per deg.

Try 421.05261 in steps per, Dose it make a full 10 deg or 360 deg now.

Check it both ways there can be allot of backlash in a std. worm gear table.

Do you have the "Use diameter for Feed-rate" Checked in Config, Tool-Path Configuration page and using a "Rotational Diameter" in the Settings page.

Been awhile since I had my rotary table setup.

Hope this Helps, Chip

Offline jimpinder

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Re: 4th axis setup
« Reply #2 on: June 20, 2008, 01:53:50 AM »
I am very sorry - but I must disgree with Chip once again about the adjustment of your number of steps per unit. For some reason he seems to think that you can fiddle about with that until you get things right. This is not correct.

Your Maths for working out the number of steps per unit are correct, and 400 is the right answer. Why on earth anyone should make a rotary table that required 421.05261 turns per rev is beyond me - or are standards so sloppy that is how it turns out. It must be the heat.

The correct way to test this is as follows.  Jog the table clockwise. Mark a position on the table - where the rotating part meets the body. A pencil line will do (across the join). Instruct the computer (G0 or G1) to turn the table 360 degrees - again clockwise . The pencil mark should then line up again.

If the pencil marks do not line up then I will agree that the screw thread is not accurate - but I personally would send it back if it is only accurate to 5%

To check backlash - use the scale on the table. Move the table clockwise to a convenient position e.g. 0 degrees or similar. Instruct the computer to move the table again clockwise by 10 degrees. If your steps per unit are accurate and your screw thread is accurate and the scale is accurate your scale should now read 10 degrees. Instruct the computer to move it back to 0 and see how the scale reads. It should be zero, but if you have backlash, it will not be. This is the amount of backlash and should be entered in the backlash table.

Make sure A is angular is ticked on the general config page otherwise if you change from inches to mm and vica versa, the A axis will change too - you don't want it to.

As far as speed goes - I am not sure what you are saying - you seem to have the speed set at 4000, that is a revolution of the table in 5 seconds (at rapid speed) - I am not sure what you are set up in - mm or inches - looking at the other speeds, I would think mm or you are going into orbit.
When you put in a command g1, use the s command to dictate the speed. I do not know what rate is set for the A axis to revert to. Is the jog any different from a g1
Not me driving the engine - I'm better looking.
Re: 4th axis setup
« Reply #3 on: June 20, 2008, 06:20:38 AM »
Hi Chris / jim

Many thanks for the help.

I have altered the settings and the speed is working a treat, I have had to turn the vel / acc

down to a similar level to the other axis now. Result.

Now that it is moving easily I will have had a better chance to play.

(previously it was taking about 2 mins to move 10 deg)

I think the accuracy problem was my fault. I was trying it out using MDI

screen G01 A10 expecting it to rotate by 10 degs instead it moved to angle 10 deg

a relative / absolute mistake. what threw me was that the readings we so close.

Only problem now is I have noticed there is an intermittent electrical fault on one

of the wires which I will need to find. When doing a large rotation the movement

occasionally stops even though the dro says it is still moving.

Will try to sort this out and let you know what the final answer was.

Many thanks for your help

Cheers George
Re: 4th axis setup
« Reply #4 on: June 23, 2008, 07:13:04 AM »
Hi Chris / Jim

Many thanks for your help guys

sorted out electrical fault (geckodrive terminal had bad connection)

All appears to be working well now but

Steep learning curve ahead.

Cheers George