Motion control L33-ERM

[jape]

I have what might be an unusual question. I would like to use motion controls to simplify the calculations for what amounts to a robotic arm. It is in 3 sections each limited to +/-45 degrees mounted on a slew. Each section is controlled by a hydraulic valve with an operator input telling the end of the arm where they want it to go. The question is, is it possible to use the inbuilt motion control functions in Studio 5000 to control the arms using encoder and valve feedback and not a servo drive?

Thanks

[Ken Roach]

That's a big topic that prompts a bunch of of inquiries about whether the hydraulics and feedback devices can provide "servo like" control in the first place, and whether the control you want to do is within the abilities of ControlLogix kinematics.

A good handbook for understanding what sort of robot mechanisms can be controlled by ControlLogix coordinated motion kinematics is the MOTION-UM002 Motion Coordinate System user manual:

https://literature.rockwellautomatio...m002_-en-p.pdf

I think the question in between is "can I connect a Virtual Axis to hydraulic servo controller" or even "can I use ordinary non-motion-control I/O to control a hydraulic component, which in turn follows a ControlLogix virtual axis".

The usual answer to "can I use ControlLogix to run a servo hydraulic axis" is "you should use a purpose-built controller instead".

Please describe the mechanism in a little more detail, maybe with a photo or model or diagram. While you described the mechanism as being hydraulically driven, you didn't say if it uses rotary hydraulic motors or actuators, or if it uses hydraulic cylinders.

Do you have the ability to choose the hydraulic pumps and valves, or are you being asked to control an existing system ?

[jape]

Thanks for the prompt reply. I’ll try and do a diagram a little bit later. To answer your questions.

1. This is something that I’ve been asked to integrate into our control system. The hydraulic pumps/ valves and the arm have been sourced from different vendors
2. The arm itself sits on a slew so it can spin around and be put into position or stored
3. Each linkage on the arm is controlled by 2 parallel cylinders which limits the moment of the arm by +/-45 degrees. This was done to achieve the rotational speed required. Each arm section is the same but the length of the first arm in the x-y axis changes with the raising and lowering of the arm
4. The actual position of the end of the arm isn’t super important. Just that it moderately track what the operator wants it to do
5. Ramp up, down, abrupt stops are important to manage as they will cause the equipment to shake

To summarize the design without a photo, it’s a 3 linkage cork line stacker with activators like on a king pin on an excavator.

From your comment I take it that I should not bother with trying the motion controls or trying to use them in a situation which they weren’t expressed built for.

I was going to take the position and velocity feedback to calculate the position and movement of the tool and just ensure that it wasn’t travelling too quickly and generally in the direction that the operator wanted it to. Mostly ive just been a little intimidated in trying to do the math required to calculate how each linkage should attempt to move.

In the absence of not using servo control nor requiring precise control of the arm do you have any advice on implementing this in studio 5000?

So far I’ve
1. Written controls to calculate the position and velocity of each arm both relative to the base and to the arm itself
2. Written controls on controlling the hydraulic valves by telling them the speed I want to go and the direction

[Peter Nachtwey]

I would use a hydraulic servo controller that was designed to do these kinds of applications. You can still use a PLC but the motion controller does all the heavy lifting.

Is the motion always the same?


Usually the big problem in these kinds of applications is the mechanical/hydraulic design and figuring out how to work around the problems.
It appears there is a lot of non-linear motion.
Ramp up and ramp down limitations aren't a problem
Usually just having the position is enough to define a spline. Then ramping up and down and over all speed to achieve by change the speed of the index into the spline(s).

[jape]

Hello Peter,

I’ve reached out to a delta supplier for the controller. I was having a few thoughts about it last night and if the arm I’m in the motion controller, then the boat should easiest be able to be controlled via the motion controller as well (as essentially it is the same principle). All that would be left would be to integrate the joysticks, and valves back to the motion controller as well. The drives are on Ethernet/IP and Modbus currently but could be switched to the canbus as well.

I think if that’s the case the AB controller becomes redundant.