Hardware for a 6 axis Puma robot

Hi folks,

I'm running a Puma 560 6-axis robot in my workshop and getting 2 additional Puma arms soon. The original controller is noisy, heavy and not very reliable on the long run (>25 years old). I'm planning to exchange the controller by something controlled via LinuxCNC. There is a Puma configuration for LinuxCNC available.
Now my questions on the right hardware configuration:
Since it is a 6 axis robot I have to keep an eye on the cost.
My current idea is to use Uhu servo controller with a standard breakout board for the parallel port (should support up to 6 tact/dir signals). This looks like the most inexpensive solution (65,-- EUR each servo controller + 20,-- EUR for the ParPort board + 50,-- for the power units). I'm already using one Uhu controller on my other 4 axis robot and this works fine (but only 1 axis is a servo - all others are stepper).
Now the questions:
- will this easy setup work or do you see issues with controlling 6 axis via tact/dir signals? High speed is not really required.
- the axis are controlled independently via the Uhu controllers and the encoder feedback is not reaching LinuxCNC but only the servo controller boards. Velocity and acceleration is controlled by LinuxCNC and additionally by the Uhu - will this double control cause problems?
- is there a better setup by using some other components (e.g. MESA boards). Please no recommendations of solutions in the > 1000,-- EUR range. The robot has 60V servos with normal encoders all together ~500W.
- Is LinuxCNC a good approach at all or would you recommend something else. My 4 axis robot is running fine with LinuxCNC with self coded kinematics.

Would be nice to get your recommendations.

You could use Mesa cards and not spend so much money (much less than 1000 €) and have a full encoder feedback to LinuxCNC.

A 7i77 can connect up to 6 axis and receive the encoder feedback, if your servos accept analog voltage as the input:
www.wiki.eusurplus.com/index.php?title=7i77
eusurplus.com/index.php?route=product/pr...ue&sub_category=true

If you need step and direction, you can use the 7i76 that it up to 5 axis. You can then use another card on the extra DB25 of the 5i25 to handle the 6th axis.

to use it, just need a 5i25 or a 6i25 depending on your motherboard.
Not expensive with a lot of possibility's to expand if you need more IO's

robottom wrote:

Hi folks,

- is there a better setup by using some other components (e.g. MESA boards). Please no recommendations of solutions in the > 1000,-- EUR range. The robot has 60V servos with normal encoders all together ~500W.

I have several users using the Pico Systems PWM controller and PWM servo amps on robots. Most have
brushless motors, not sure what type of motor is on the Puma. I have real doubts you can do this under
1000 Euro. 6 axes in our PWM system would cost US $1250 for brush-type motors, or US $1400
for brushless, assuming that it has standard encoders with "Hall" signals. We have various
converters for some of the proprietary encoder systems.

- Is LinuxCNC a good approach at all or would you recommend something else. My 4 axis robot is running fine with LinuxCNC with self coded kinematics.

LinuxCNC is the ONLY solution that truly handles robot kinematics under probably $50K.

Jon

Many thanks for your replies.

@Jon: thanks a lot! This at least shows me that I'm not on a completely wrong track with LinuxCNC. The Puma has brush-type motors with normal quadrature encoders (250 units per rev.). The Pico Systems are a bit above budget but I will keep it as an option

@emcPT: I also looked into the 7i77 together with the 5i25 but as far as I could see this will only replace the digital servo boards of the current Puma controller. I still would need servo amps with +/-10V input. This is why I'm in favor of the UHU servo controller. It comes with everything on one single board (enhanced PID controller, encoder input and power amp part) so you can directly connect to the servo motor. My concern in this setup is that LinuxCNC does not get any feedback on the servo motor position. This will completely handled inside the UHU board. Do you share this concern. Can this cause problems in the motion control of all axis together or just a limitation I can live with? How is this handled in a 7i77 and 5i25 setup. Will there a feedback to the LinuxCNC about the absolute position or is this also kept locally per joint inside the 7i77 (e.g. if I power off the servo motor for one joint, release the brake and move the joint manually will this be recognized by LinuxCNC or will this trigger only an error (german: Schleppfehler) on the servo board?

robottom wrote:

Many thanks for your replies.
@emcPT: I also looked into the 7i77 together with the 5i25 but as far as I could see this will only replace the digital servo boards of the current Puma controller. I still would need servo amps with +/-10V input. This is why I'm in favor of the UHU servo controller. It comes with everything on one single board (enhanced PID controller, encoder input and power amp part) so you can directly connect to the servo motor. My concern in this setup is that LinuxCNC does not get any feedback on the servo motor position.

What type of signal does then the UHU is expecting? If it is step and direction you can use the 7i76 (but still without encoder feedback to LinuxCNC) that can be supressed using an encoder Mesa card, where you would take the encoder signals that currently go to the UHU and will also go the the Mesa encoder card (this is, the signal will go to both LinuxCNC and your controller).

robottom wrote:

This will completely handled inside the UHU board. Do you share this concern. Can this cause problems in the motion control of all axis together or just a limitation I can live with? How is this handled in a 7i77 and 5i25 setup. Will there a feedback to the LinuxCNC about the absolute position or is this also kept locally per joint inside the 7i77 (e.g. if I power off the servo motor for one joint, release the brake and move the joint manually will this be recognized by LinuxCNC or will this trigger only an error (german: Schleppfehler) on the servo board?

If you want feedback to LinuxCNC, then also an inexpensive solution would be 5i20 + 7i47 (6 step+dir + 6 encoders) + another card for IO.
I do not have in stock but I ordered stuff from mesa that will depart on 03 / Mar /2015 from USA, so you could save in shipping.
Maybe the more knowledge people will reply, but I think I did not made a mistake on choosing the correct boards.

o.k. I see. It looks like I need some kind of servo amp in any case and it is not included in any of those cards.
I'm not sure if it really make sense to have the encoder feedback both on the UHU board and on the MESA cards and use the tact/dir signals. This looks like a mixture of encoder usage.
I see 2 possible setups: 1. use the old servo amps in combination with a 7i77 MESA cards or 2. use the UHU setup and only use a MESA FPGA Card in front.

Thanks a lot!

I missed the info that you do not have any servo amps. If you require servo amps Mesa also offers several solutions, but I would need more info about your motors. Are they DC? You said 500w, but for each motor, or all together? (I googled and the puma robots seam quite small, so I presume that they are DC)
If you are able to sacrifice a bit on speed (voltage normally reflects more on speed), you could use a single 7i54 that can drive up to 6 motors ! This would become quite cost friendly. Please check if 40V 3amps are suitable.

Uhus are a very, very good solution for your pupose. I am pretty sure that two parports will do a reliable job and if you get speed problems, you still have the option to get a Mesa card.

Do you know the Blast from Benezan? DC servo amplifier, good, reliable and not to expensive.

Norbert

I must say that I do not have an idea what is the UHU. And I am confused, have you or not the servo drive/amplifiers? If you have them, why do you consider in changing them?

@emcPT: I do have the servo amps from the old controller. Since I don't know exactly if they work with +/-10V input and since my plan was NOT to reuse any of the >25 years old electronics of the current controller I was looking for something inexpensive replacing everything of the old controller.
Infos about the UHU you can find here: www.uhu-servo.de/. This is a inexpensive solution (if you solder it yourself) and I'm already using one of the UHU boards on another robot and I satisfied.
My current servo amps are driven by a 60V 500W power supply unit - 40V might be a bit too small. As far as I know the 3 bigger joints have 160W DC servo motor while the 3 wrist joints are driven by 80W DC servo motors. I also saw the 7i54 before but I feared it is a bit too small - buy it just for a test if 40V are sufficient is a bit to expensive/risky.

@newbynobi: yes I know the Benezan items and on my other robot I considered to use it. The Benezan Uhu is 160,-- EUR thus 2-3 times the price of a self made solution but still o.k. For the 6 axis it would mean 1000,-- EUR what is already it my upper limit. I thought the blast is for AC servos. The Puma is using DC servos.
I guess I will give the UHU approach a try and use for the first test a parport interface with my old Thinkpad laptops as I'm using for my other 4 axis robot. One parport will only serve the 6 axis tact/dir and nothing else. This means a seconde parport would be required for later "productive" usage.
Does anybody know if I can add another PCMCIA parport card to my Thinkpad and this will work with LinuxCNC? This would be the ideal solution since I don't want to put a desktop PC in my workshop.

Thanks again for all your support.