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Author Topic: My own robotic arm-some progress  (Read 1884 times)

krolikbest

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Re: My own robotic arm-some progress
« Reply #15 on: July 05, 2018, 11:14:24 pm »
Thanks, but the deeper in the forest, the harder way.. :)  In next week I'm going to improve serial reading from uC via i2c. Still dissatisfied.

avra

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krolikbest

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Re: My own robotic arm-some progress
« Reply #17 on: July 06, 2018, 03:40:28 pm »
Thanks Avra, useful gear planning. Especially with export to hpgl and dxf. this two formats I have in my program for milling machine.

tr_escape

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Re: My own robotic arm-some progress
« Reply #18 on: July 06, 2018, 07:05:02 pm »
Thanks Avra, useful gear planning. Especially with export to hpgl and dxf. this two formats I have in my program for milling machine.

Actually your project spectacular and I would like to know more details about your project;

* Which controller do you using? Servo driver or PLC? or maybe some circuit designed by yourself.
* Is lazarus using as main development tool? or do you using as supervisory software?


marcov

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Re: My own robotic arm-some progress
« Reply #19 on: July 06, 2018, 07:25:04 pm »
Probably our robot will be aluminium.

Last week I got the word, that even if we are going to deliver that machine, the robot will be externally bought. :crying.

The only project to look forward to is trying to improve a basic microstepping motor. (read back position via quadrature and adjust rate to make it even smoother)

This week I also got a sample of dspic33CH, the first dual-core (*) uc I've used.

(*) not dual core with shared memory like PCs. It is more two separate cores connected via register based mailslots. You can also assign pins to either core or slave. Mostly meant to have a tight kind of motor feedback on the slave (which is rumoured to be extremely fast. 100 MHz/Mips and nearly any instruction is 1 cycle, except branch and read-write-modify are 2), and the "rest" +communications on the 90Mhz/Mips master (which takes 4 cycle hit for a branch, so also a bit less efficient)
« Last Edit: July 06, 2018, 07:29:09 pm by marcov »

taazz

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Re: My own robotic arm-some progress
« Reply #20 on: July 06, 2018, 07:26:17 pm »
Probably our robot will be aluminium.

Last week I got the word, that even if we are going to deliver that machine, the robot will be externally bought. :crying.
so? create a company and have them buy it from you :P
Good judgement is the result of experience … Experience is the result of bad judgement.

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marcov

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Re: My own robotic arm-some progress
« Reply #21 on: July 06, 2018, 07:31:10 pm »
so? create a company and have them buy it from you :P

One of the main reasons is that these companies that are customer don't buy robots from firms without experience. So that would also hit my "company". Worse, the objects to handle are red-hot. (literally, as in just fabricated glass bottles). Maybe not the best to begin with.

taazz

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Re: My own robotic arm-some progress
« Reply #22 on: July 06, 2018, 07:36:00 pm »
so? create a company and have them buy it from you :P

One of the main reasons is that these companies that are customer don't buy robots from firms without experience. So that would also hit my "company". Worse, the objects to handle are red-hot. (literally, as in just fabricated glass bottles). Maybe not the best to begin with.
Just to be clear, I did not mean to go to your company's customer directly, I mend your company (current employer) buy it externally from you. I did not in any way suggested to undercut your employer.
Good judgement is the result of experience … Experience is the result of bad judgement.

OS : Windows 7 64 bit
Laz: Lazarus 1.4.4 FPC 2.6.4 i386-win32-win32/win64

krolikbest

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Re: My own robotic arm-some progress
« Reply #23 on: July 11, 2018, 02:59:36 pm »

Actually your project spectacular and I would like to know more details about your project;

* Which controller do you using? Servo driver or PLC? or maybe some circuit designed by yourself.
* Is lazarus using as main development tool? or do you using as supervisory software?
Hi,

1.steppers are connected to stepper controllers M545 (all from China)

2.as a servo controller is atmega8. so one atmega for one stepper. atmega is responsible for:
- step/dir generator
- quadrature encoder reader
- some other works
- i2c communication with RPi

lazarus is used for writing the main program on RPi. Its task is to send datas i.e. velocity, distance (encoder pulses), checking errors from atmegas, interact with user. There is no "magic" libs to control servos.

TODO:
- inverse kinematic - maybe sometime
- moving robotic arm directly from a program though i don't know what is the point. I do it because my children want :)

marcov

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Re: My own robotic arm-some progress
« Reply #24 on: July 11, 2018, 03:22:13 pm »
Looks like the same stepper we use. In 25600 (25*1024) mode (because of the large number of divisors)


krolikbest

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Re: My own robotic arm-some progress
« Reply #25 on: July 11, 2018, 09:27:38 pm »
One stepper (current=6A) is connected with HSD86 (China as well). I expected that it should work most stable but with this controller I cannot set current. It sets up the current in some different way (there isn't dip switch) and in the end this stepper makes sometimes surprises (undesirable). Consider to change with M545 or MDC860.

marcov

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Re: My own robotic arm-some progress
« Reply #26 on: July 11, 2018, 11:02:30 pm »
We have some problems that even with 25600 granularity the angular speed (as in 360 degrees/25600) is not constant enough. The various microsteps are not entirely equidistant which frustrates fourier filtering of results etc.

It is however probably the motor, not the stepper. A plan to tackle this by controlling the motor directly and calibrating it is in the works, probably a project for fall.

kupferstecher

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Re: My own robotic arm-some progress
« Reply #27 on: July 12, 2018, 05:37:52 pm »
@Marcov:
Wouldn't be a servo motor more suitable if you have high requirements for position and speed?

marcov

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Re: My own robotic arm-some progress
« Reply #28 on: July 12, 2018, 07:05:04 pm »
@Marcov:
Wouldn't be a servo motor more suitable if you have high requirements for position and speed?

Afaik there is some closed loop control stepper too nowadays. Maybe the one we use has such possibilities.

It might not even the controlling of the motor, it might be that the signals for 1/(n*200) th of a rotation are emitted at the precise moment regardless of the motor's feed. This might also be possible using some interpolation of the derivative of the motion. I haven't seen the details of the plan yet.

kupferstecher

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Re: My own robotic arm-some progress
« Reply #29 on: July 12, 2018, 08:22:14 pm »
With microstepping I don't have good experience, as the holding torque partially persists. Thats why I asked.

Once I made a torque compensation for a permanent magnet synchron motor. I got the speed constant, but vibrations increased, because the constant torque needs changing current amplitudes which creates additional oscillating radial forces between rotor and stator.

 

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