I can now run EMC2 and it kind of "works"

Image "tmp-7713.jpg"

Knee is to the left (big gray slab).

Servo motor is center, with a brass square plate on the back holding your new encoder.

Passing just to the left of the upper left-hand corner of the brass plate is a long rod which also passes through a bearing of some sort cat in or welded to the side of the knee located in the lower left-hand corner of the photo, and there appears to be a crank or lever on the end of the rod. It appears to come out just under the mounting plate for the motor bracket.

At a guess -- it may be a way of remoting access to the locking screw for the vertical dovetail, but I'm not sure. It could be for almost anything. It is not present on my Boss-3, anyway.

Hmm ... perhaps remote access to the BiJur lube pump's button?

For that matter -- it almost looks as though the motor is mounted on the *back* side -- near the vertical ways instead of on the front side where it would access the leadscrew crank and dial if they were present. If so, that must make it a real pain to get to the belt to replace it.

Thanks, DoN.

It is the knee locking lever.

You are right, it is a knee vertical lock.

No, it is very easy actually. I already took the pulley and belt off for testing purposes.

i

My lathe has the servo motors with tachometers and uses encoders wired to the control, much like yours. I used, or attempted to use, velocity feed forward and think it will help your system too. As a movement is started, the following error increases to the point of the motor increasing speed to try to reduce the following error (if I of PID is used). With velocity feed forward, if you command a speed of about 50% of the maximum speed, it would feed 5V into the servos to run the commanded speed, then the PID loop would correct for errors, it doesn't have to wait for the I term to integrate the error to remove the following error. EMC has velocity feed forward but it's called something else IIRC. Is my explanation making sense? If you command a move at perhaps 25% of speed, then you already know you need 25% output to get the velocity correct and the PID control takes care of the errors. You probably don't need to worry about this just yet but keep it in mind, I think it will make a difference in how tight the system can follow a path.

RogerN

Roger, to be honest, I did not understand. At this point, I want to take a step to the side and do safety related wiring. (estop, motion power cutoff in estop, thermal switches, etc)

Yes. Y axis only.

I believe that the speed at 70v will be more like 70 or so IPM, but I am not sure. I tried to set max velocity so that the drive would "try hard".

I think that you got it.

Jon, seems easy enough, I will try it tonight. I did not see PID_MAX_VEL in EMC docs and did not set it. I will set PID_MAX_VEL to

2. I have yet to find a good page on PID tuning.

Thanks a lot.

i

Maybe a simpler way to say it, for example imagine you have to make a move at 20 inches/minute. Without VFF all motion is a result of error, when you have a large enough error to get the axis moving 20 inches/minute then it will follow. With VFF the control tells the amp to run at 20 inches/minute and the control corrects for smaller position errors. Note both are capable but the VFF forwards the speed command to the amp and the PID only has to deal with smaller errors.

After you get everything else going you can play with Halscope and watch your following error, tune the servos, etc. I'm just trying to explain this concept a little before you need it and when you are to that point you will think "Ah, that's what that idiot was talking about!".

RogerN

Roger, thanks a lot, I think that your explanation is great and I am beginning to understand. Halscope sounds like a good thing to tune the system. But I will do it later, after safety wiring.

i

[ ... ]

O.K.

Thanks, DoN.

On Thu, 15 Jul 2010 08:19:35 -0500, Ignoramus12838 wrote the following:

Surely you could find a window air conditioner and install it in the sho^H^H^Hgarage, Ig. It would also help reduce humidity in there, preventing rust on your tools and equipment. (wifely sales point)

Safety wiring is good. I mentioned this before, and will repeat: A standard trick during development is to electrically (or hydraulically in a hydraulic system) limit the max power the motor can deliver, to reduce the consequences of the inevitable mistakes during the learning curve.

Power limitation can be achieved in a number of ways. For an electric motor, a big power resistor in series is typical. Another approach is an undersized fuse or circuit breaker in series with the motor. And one can do both.

Joe Gwinn

Not sure what information you are looking for, but here is one of my favorite authors on the subject:

Kevin Gallimore

You can also find some good info by searching for PID on the Nuts and Volts magazine web site.

Dan

Do you understand PID loops?

P - Proportional I - Integral D - Derivative

Proportion is proportional to the error. If you set your cruise control for

60MPH and you are only going 55MPH then you have an error of 5MPH. There is a proportional gain Kp, this determines how much of the proportional error goes in the equation, if Kp is 2 then 10 goes into the equation to calculate the output.

Derivative is the rate of change, If your cruise control is set for 60MPH and you're going 55, you have 5MPH proportional error. But if you're 5MPH too slow but catching up fast, you may need to ease up on the throttle or you'll overshoot 60MPH. Likewise if your 5MPH too slow and slowing down (maybe a steep hill) you can stomp the throttle more. Derivative gain, Kd, determines how much effect the rate of change in error has to do with the output.

Integral is the error over time. If you have your PID cruise control set for 60MPH it will never get there without Integral because it takes some throttle (output) to get the car to 60MPH. Let's say you're driving 60MPH, hit the cruise control, Proportional error is zero, Derivative is zero, guess what, the output is zero! You'll slow down until there is enough error to hold the throttle at some speed below the setpoint. Integral integrates the error over time and causes the output required to achieve zero error, it is needed when an output is needed for zero error, such as the cruise control or often a temperature control, or even a motion control in a vertical application or under a load.

Though not the scientific method, I raise proportional gain until it becomes unstable, then back it off a bit. Then I do the same with Derivative, then re-do proportional, back an forth a couple times until I have P and D controlling but well into the stable region. Then I work on I gain. One way is to put a little torque on the shaft to see some error, turn up I gain until it gets rid of disturbances on the shaft as fast as possible without oscillation.

For my lathe with tach feedback, I have D gain set to 0, the amp does enough that any D gain in the control seems to make it oscillate.

Hope this helps!

RogerN