Hydraulic 6-axis Robotic Arm EMC Configuration

Hydraulics

The emc configuration is for a robotic arm that moves based on the rotation of 6 hydraulic motors.

These hydraulic motors are powered by a hydraulic circuit that contains:

*Single-displacement pump (generates the flow)

*Pressure relief valve (to maintain continuity of flow without any bursting failure)

*6 solenoid valves (for directional control of hydraulic fluid)

*6 stepper-controlled needle valves at 16GPM each (for flow control of hydraulic fluid)

Note: proportional servovalves were considered but were prohibitively expensive (cheap ones starting at 2000 dollars)

Feedback

Positioning feedback is granted through 6 incremental encoders; the resolution to work with is 10,000 pulses per revolution for the initial prototype going all the way to 5 million ppr for future development. These encoders are directly wired to the microcontroller.

Control System - Software

As far as I know, the software side of the control system requires:

*Properly written HAL file

*EMC2 program

Control System - Hardware

And the hardware side of the control system requires:

*Microcontroller with parallel port connection

*6 channels from stepper motor drivers

*6 channels from solenoid drivers

*Power supply

Advice on improvements to this overall system would be appreciated, but the major challenge is how to configure the software-related elements (emc). I have no experience writing HAL files but do know how to attain Denavit-Hartenberg Parameters and a bit of theory on how genserkins allows emc to control a 6-axis robotic arm. I think I am stuck in theoryland regarding configuration.

Thanks in advance. I greatly appreciate all help on this. Once all of this configuration gets sorted out, concise build, programming, and testing instructions are going on the Open Source Ecology wiki under "industrial robot."

you will not be able to control 6 axis via the parrall port with sufficent I/0 left for limits or other switches
i suggest you concider on using either Mesa 5i20 /5i22 or similar pico products , that wil make your conversion much easier .

You might want to look at a variable displacement pump or add a very large oil cooler. At any rate oil flowing over needle valves spell heat.

How big this this robot going to be? If it going to be a small one look at driving it directly with the steppers. With hydraulics any way you go about it they leak. That why Hydraulics is my last choice in power systems

What GPM are your valves going to be? Back in my motion base days, we replaced $8000 servo valves with $2000 prop valves. Mind you these were 80 GPM valves. The servos were shanck-pegesaus (sp?) and the props were rexroth. I would think 15 years later you could get the props for less espacially if they don't need to be that big.

Also, depending on the flow rates, you might be able to use proportional cartridge valves, much cheaper.

Btw, we had 3 axis doing average of 100 reversals per minute with the props. As it was a ride, we had 1/16 inch following limit and the machine weighed in at 20,000 pounds.

Of course you will still need the feedback, but it will be more like a servo setup to Emc. Don't forget, you can gang the cartridge valves together for higher flow. Tell us more about the system please.

Not that the microcontroller is impossible, but you are reinventing the wheel.

but Andy it's more fun this way. I almost have my card done to control 10 steppers with limit and home switches plus a few extra io for good measure. Of course Emc can only control 9 axis, but I figure I might need a slave someday too. Having said that, for me this is a fun project aimed at learning. When I am ready to convert my money makers I will be heading over to the Mesa store myself. Nothing like tried and true equipment.

btvpimill wrote:

What GPM are your valves going to be? Back in my motion base days, we replaced $8000 servo valves with $2000 prop valves. Mind you these were 80 GPM valves. The servos were shanck-pegesaus (sp?) and the props were rexroth. I would think 15 years later you could get the props for less espacially if they don't need to be that big.

Also, depending on the flow rates, you might be able to use proportional cartridge valves, much cheaper.

Btw, we had 3 axis doing average of 100 reversals per minute with the props. As it was a ride, we had 1/16 inch following limit and the machine weighed in at 20,000 pounds.

Of course you will still need the feedback, but it will be more like a servo setup to Emc. Don't forget, you can gang the cartridge valves together for higher flow. Tell us more about the system please.

As edited in the first post, the stepper-controlled needle valves have a 0 to 16gpm range of operation. Explain more about these proportional valves please; as far as I know, they are like solenoid valves except they have infinitely variable flow control, from zero up to a maximum. What is the price range on them as well?

Well I have been looking, so far I came up with maybe a hydraforce pv72-20. Maybe this will work for you. I haven't been able to find a price yet.

andypugh wrote:

An interesting idea I investigated when trying to design an actuator to reach 50mph in 0.5" and then travel at a controlled and reducing speed for a further 2" was a binary array of valves.

Each valve is twice the flow of the one next to it, and they add up to the max flow. If you have 8 of them, and connect each to one bit of a binary number, you get 256 discrete flow rates, and potentially very fast operation.

I think I am seeing proportional valves of the right sort of flow rate for £200 or thereabouts.
uk.rs-online.com/web/p/valves/7040389/

The binary array of valves does not seem optimal in this case as cost (8 valves per axis totals a lot) and rough operation (proportional valves or step motor microstepping appears to be a smoother alternative).

The link is to a solenoid valve, which does not grant infinitely variable flow control; this 3-position type of valve is designed for full forward, full reverse, and either open or closed neutral. A solenoid valve has been already selected for use in the industrial robot as to provide directional control.