3-axis closed loop motion control

3-axis closed loop motion control Greetings! I'm a long-time hacker who hasn't had much time for anything except scavenging parts until recently. Now that I've got a 3d printer, a lot of projects seem much more in reach, and I wish to contribute to the world of OSHW 3d printers. The thing about scavenging for parts is, you inevitably take apart a lot of 2d printers, and as such you end up realizing that newer printers don't use steppers anymore, with obvious cost benefits. It's clear that 2d printing quality has increased, while cost to manufacture has decreased. I suspect stepper motors are about as cheap as they can get atm, so the next breakthrough in reducing printer cost is going to be DC motors. What's I'd like to do then, is to develop fully closed-loop DC motor control in 3 axis, WITHOUT pretending to be a stepper. Projects just as https://hackaday.io/project/15025-tarocco exist, but they don't go all the way: [list=1] [*] they are emulating steppers, with STEP and DIR signals. this is nice in that you don't have to re-write firmware, but it doesn't take full advantage of a DC motor's continuous feed rate, as opposed to a stepper's steps [*] they generally rely on on-shaft quadrature control, which is nice if you have a 0-backlash ballscrew, but not so helpful in controlling position if you've got a $2 piece of threaded rod that's bent in a few places [/list] The benefits of closed-loop control should be pretty obvious: [list=1] [*] cheap DC motors instead of steppers, for a given torque [*] no skipped steps ruining prints [*] smoother motion profiles, as DC motors are ramped up & down [/list] Downsides are: [list=1] [*] more expensive electronics (faster uC's, mainly, and these are getting cheaper every day) [*] additional parts (encoder, strip) [*] more complex firmware [/list] My purpose in posting here is twofold: First, I want to know if anyone knows of similar project. NIH is not a problem for me, if there's another OSHW project out there doing this, I'd love to contribute to its development. There are at least two closed-source implementations I've come across, and one of them I *believe* is using on-shaft encoders, not linear ones, it's possible both are. Second, does anyone know where I can get optical encoding strips for cheap? I could get them by just gutting a few identical printers would get me enough strips to be going on with, but that's hardly an ideal, from a manufacturing standpoint. https://reprap.org/forum/read.php?1,738012,738012#msg-738012 Fri, 14 Aug 2026 00:00:00 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?1,738012,794146#msg-794146 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,794146#msg-794146
I think GT2 is ok and we can use the motor attached encoder with 1024 ppr just fine.

But if you want to go crazier,

Looking on Optical strip, there are cheap and they are used in large format inkjet printer or you can go to the stencil/printing/plating mask film company they can go down to 10um resolution(industrial standard).
But if you want to use magnetic strip, it might be a good choice you can find magnetic strip and reader ic from many vendors.

However if you want to go to sub micron, you can try laser interference as well, think about using a laser time of flight sensor and let them bouncing a thousand time across two parallel mirror. you can readout the distance in many km and divide into sub micron accuracy due to the nature of time of flight reading which the error is the constant latency delay.

Or you can use multi different encoder strip pitch with different prime number. the you can calculate the resolution up to a million factor sue to there just a few prime numbers construct in to a million.]]> bnarit General Sat, 28 Oct 2017 17:05:27 -0400 https://reprap.org/forum/read.php?1,738012,794144#msg-794144 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,794144#msg-794144
I have built several 3d printer too, i'm currently working on my 18th revision and currently my 30th printer.

What I have try in these few years. The theoretical of Stepper and DC motor might conclude the superior of DC motor (not mention Direct Drive Brushless Linear Actuator). For some example such as in the industrial 3d printer they use Close loop DC motor.

But Why dose a close loop dc failed in hobby grade. Well, there is/are 3d printer project(s) many years ago that promises the advantages of DC Brushed Close loop motor by reference from the commercial inkjet printer.

The problem of dc brush/brushless motor you have to archive is...

1. DC torque vs Stepper Holding torque. Imagine one axis is hold and the other is moving, and there is some coupling force. Without breaking system, the vibration will effect the holding motor due to low holding force of dc (unless you will need to use a dc with bigger size and a good winding inside which we prefer Maxon,Faulhaber,any Coreless for ex) and If ther is no error there wont be any force. If you crack down PID algorithm, there must be some error or movement for encoder to sense and feed into the PID gain to energize power to motor.
2. Synchronization, the success in large scale CNC or Robot that use dc close loop is they calculate their kinematic of multiple axis together. They use a vector drive scheme which is the technique to sync the error of each motor in realtime.
What I'm talking about is in every system there will be error. In stepper motor control the error we are talking is not the step missing but the deviation from the desired position in microstepping (which is the major cause of Salmon skin effect).
In PID there must be Overshoot, Lagging and steady-state error which is need to compensate. If one axis has error more than other axis that means the current of the current state is not on the planned trajectory which a new heading vector (or angle) must be recalculate in each iteration.
3. In the end, then normally we feed the velocity control loop with the step/ direction signal to make sure that the feedrate is constant. you can implement in PID loop but the equation is the same.

Normally in motor control, we gonna use layers of control-loop , stacked on each other.
For ex. Trajectory(Step/Dir) ->Position Control(PID with position feedback from encoder -> Velocity (PID with calculated speed from encoder(Poor) + Back EMF Voltage from motor(need kalman filtration !!sophisticate!! )) -> Acceleration (aka Electric Current loop) sense from resistor or hall device.]]> bnarit General Sat, 28 Oct 2017 16:51:15 -0400 https://reprap.org/forum/read.php?1,738012,788798#msg-788798 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,788798#msg-788798 [www.panowin.com]

or its first vid on this page
[www.panowin.com]]]> MechaBits General Tue, 19 Sep 2017 03:23:22 -0400 https://reprap.org/forum/read.php?1,738012,788757#msg-788757 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,788757#msg-788757
I highly doubt that stepper motors are limiting print quality in hobby FDM. Stepper motors are by far the best performing option for their cost, which is why they are used everywhere.]]> 691175002 General Mon, 18 Sep 2017 15:47:10 -0400 https://reprap.org/forum/read.php?1,738012,788540#msg-788540 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,788540#msg-788540 bearer General Sat, 16 Sep 2017 18:13:24 -0400 https://reprap.org/forum/read.php?1,738012,746471#msg-746471 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,746471#msg-746471

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I got MPU 6050 IMU hooked up
what should I measure?

Awesome coincidence... I should read more subforums.

Is it raw IMU-data you're getting now?
I'm no expert in vector algebra, but the Skrogh-guy seems to be.
All I know is, you have to calculate acceleration vector over time to get a movement as result. My tech/math English vocabulary is to limited to explain.]]> o_lampe General Wed, 08 Feb 2017 02:04:17 -0500 https://reprap.org/forum/read.php?1,738012,746399#msg-746399 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,746399#msg-746399
[forums.reprap.org]

[forums.reprap.org]

I got MPU 6050 IMU hooked up
what should I measure?

MPU6050 6-axis MotionTracking device that combines a 3-axis
gyroscope, 3-axis accelerometer, and a Digital Motion Processor™ (DMP) all in a small 4x4x0.9mm
package.

:S]]> cozmicray General Tue, 07 Feb 2017 18:25:55 -0500 https://reprap.org/forum/read.php?1,738012,746286#msg-746286 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,746286#msg-746286

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o_lampe
I've built a self balancing robot with such a sensor and it regulates so fast, you don't see or hear it.

I must put that on the todo list. Self-balancers have always seemed amazingly cool.]]> JamesK General Tue, 07 Feb 2017 13:34:52 -0500 https://reprap.org/forum/read.php?1,738012,746284#msg-746284 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,746284#msg-746284 self balancing robot with such a sensor and it regulates so fast, you don't see or hear it.]]> o_lampe General Tue, 07 Feb 2017 13:32:29 -0500 https://reprap.org/forum/read.php?1,738012,746139#msg-746139 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,746139#msg-746139 AleksClark General Tue, 07 Feb 2017 06:05:43 -0500 https://reprap.org/forum/read.php?1,738012,746111#msg-746111 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,746111#msg-746111
Multicopters are stabilized by a 6DOF gyro/accel sensor MPU6050. They are very sensitive, but tend to drift.
With a coarse encoder strip or wheel and the MPU data to navigate "between" the encoder signals, we would have a stable feedback loop.

There is plenty of code for arduinos about sensor fusion with MPU6050 and other ( magnetic ) sensors, so we wouldn't have to invent the wheel.]]> o_lampe General Tue, 07 Feb 2017 03:52:31 -0500 https://reprap.org/forum/read.php?1,738012,739219#msg-739219 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,739219#msg-739219 dc42 General Mon, 16 Jan 2017 03:18:30 -0500 https://reprap.org/forum/read.php?1,738012,739057#msg-739057 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,739057#msg-739057

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dc42
If we can come up with a good combination of BLDC motor and control IC, I'm up for implementing the necessary support in RepRapFirmware.

Sounds like a plan!

I suggest we could start with a hall sensor pcb that fits a wide variety of BL outrunners. I would also volunteer to rewind them to a lower kV if necessary. ( That's what I did at Plettenberg-Motoren , com all day long )

Maybe we can use a mouse sensor aimed to the can of the outrunner as "shaft" encoder?]]> o_lampe General Sun, 15 Jan 2017 13:29:44 -0500 https://reprap.org/forum/read.php?1,738012,738960#msg-738960 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738960#msg-738960
If we can come up with a good combination of BLDC motor and control IC, I'm up for implementing the necessary support in RepRapFirmware.]]> dc42 General Sun, 15 Jan 2017 08:38:37 -0500 https://reprap.org/forum/read.php?1,738012,738956#msg-738956 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738956#msg-738956

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dc42
IMO it definitely makes sense to do the motor control and sensor processing in a separate processor. You can get an ARM processor for about £0.50 now - less than the cost of an attiny - so there is no reason not to use one per motor.

They are definitely cheap these days. If two encoders were used (shaft and axis), there's a much larger chance it would make sense. I really don't want to just emulate steppers though, so figuring out what communication needs to happen is going to be tricky. At the very least I think each axis is going to need to know what the 'next move' is to properly plan the acceleration curves, which will be easier to do if it's a subroutine in a single processor that's receiving the GCode (do I even WANT to use gcode, is another question. Standards are awesome and everything speaks it but I've read people complaining about its limitations)]]> AleksClark General Sun, 15 Jan 2017 08:24:49 -0500 https://reprap.org/forum/read.php?1,738012,738888#msg-738888 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738888#msg-738888

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o_lampe
the L6234D chip is a 3phase H-bridge, able to control one BLDC motor or three DC motors

8-)

Sorry about that statement.
I had the L298 Driver in mind, which can drive one stepper or two dc motors and extrapolated from there...(td)]]> o_lampe General Sun, 15 Jan 2017 03:04:34 -0500 https://reprap.org/forum/read.php?1,738012,738832#msg-738832 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738832#msg-738832 dc42 General Sat, 14 Jan 2017 17:46:08 -0500 https://reprap.org/forum/read.php?1,738012,738824#msg-738824 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738824#msg-738824

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o_lampe
I've spent a few minutes over at hackaday and there are several ( robotic- ) projects using optical mouse sensors. They mostly failed, due to top speed of the robot or dirt/ distance to surface issues. All of that can be ignored in our application, but the max. speed might still be an issue.

The reliability of the encoder signal can be greatly improved by sensor fusion, but for 3 axis and ( several ) extruders, it takes a lot of CPU time to maintain all those sensors. Maybe an independent controller for each motor which only reports errors to the main CPU is the better way.

The idea of only adding a mouse sensor is pretty seductive, but I agree the cpu overhead is likely prohibitive. To keep costs inline with current controller boards I'd like to do it in a single MCU, some flavor of ARM most likely.]]> AleksClark General Sat, 14 Jan 2017 17:23:25 -0500 https://reprap.org/forum/read.php?1,738012,738754#msg-738754 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738754#msg-738754
The reliability of the encoder signal can be greatly improved by sensor fusion, but for 3 axis and ( several ) extruders, it takes a lot of CPU time to maintain all those sensors. Maybe an independent controller for each motor which only reports errors to the main CPU is the better way.]]> o_lampe General Sat, 14 Jan 2017 13:53:41 -0500 https://reprap.org/forum/read.php?1,738012,738737#msg-738737 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738737#msg-738737
I've used hall-sensors to "upgrade" sensorless BLDC motors. Maybe with the right hall sensors it is possible to implement some kind of encoder.
If not, it is a way to reverse direction in a safe and reliable way.

Three sensors with bipolar output x 14 magnets.
It's beyond my knowledge, how many differential signals per rev this would actually make. But what's good enough for camera gimbals should also work for closed loop printers. Especially when we combine it with the external optical mouse sensor/encoder.]]> o_lampe General Sat, 14 Jan 2017 12:42:13 -0500 https://reprap.org/forum/read.php?1,738012,738700#msg-738700 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738700#msg-738700
I have about a dozen of these on various craft:
[www.banggood.com]

The firmware is open source as well:
[github.com]

Cheaper options exist if you want to buy multiple ESCs on the one board:
[www.readytoflyquads.com]

The main issue with these controllers is that they don't handle low speeds all that well. Reversing is getting better with the newer software, some people (including me) have dabbled in quadcopters that can hover upside down, which requires the motors to reverse direction quickly. This is directly applicable to our situation.

I get the feeling that the brushless solution would take a lot of effort to get to be as precise as a simple stepper motor, however.]]> nebbian General Sat, 14 Jan 2017 09:09:35 -0500 https://reprap.org/forum/read.php?1,738012,738689#msg-738689 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738689#msg-738689 dc42 General Sat, 14 Jan 2017 08:08:17 -0500 https://reprap.org/forum/read.php?1,738012,738668#msg-738668 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738668#msg-738668

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dc42

Quote
bobc

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o_lampe
I agree with David, brushes can wear out, but a DC motor is so much easier to control.
E. g. the L6234D chip is a 3phase H-bridge, able to control one BLDC motor or three DC motors. It would be a good starting point for a new generation of controllers.

That's a triple half bridge, I think for bi-directional control you need a full bridge. There seem to be a lot of driver chips for small motors though, as noted cars are now full of them!

A triple half bridge is sufficient. See [www.digikey.co.uk].

Derp. For brushless DC yes, not three DC motors. See [en.wikipedia.org]]]> bobc General Sat, 14 Jan 2017 07:16:25 -0500 https://reprap.org/forum/read.php?1,738012,738660#msg-738660 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738660#msg-738660

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bobc

Quote
o_lampe
I agree with David, brushes can wear out, but a DC motor is so much easier to control.
E. g. the L6234D chip is a 3phase H-bridge, able to control one BLDC motor or three DC motors. It would be a good starting point for a new generation of controllers.

That's a triple half bridge, I think for bi-directional control you need a full bridge. There seem to be a lot of driver chips for small motors though, as noted cars are now full of them!

A triple half bridge is sufficient. See [www.digikey.co.uk].]]> dc42 General Sat, 14 Jan 2017 06:52:34 -0500 https://reprap.org/forum/read.php?1,738012,738648#msg-738648 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738648#msg-738648

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o_lampe
I agree with David, brushes can wear out, but a DC motor is so much easier to control.
E. g. the L6234D chip is a 3phase H-bridge, able to control one BLDC motor or three DC motors. It would be a good starting point for a new generation of controllers.

That's a triple half bridge, I think for bi-directional control you need a full bridge. There seem to be a lot of driver chips for small motors though, as noted cars are now full of them!]]> bobc General Sat, 14 Jan 2017 06:10:31 -0500 https://reprap.org/forum/read.php?1,738012,738611#msg-738611 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738611#msg-738611 E. g. the L6234D chip is a 3phase H-bridge, able to control one BLDC motor or three DC motors. It would be a good starting point for a new generation of controllers.]]> o_lampe General Sat, 14 Jan 2017 03:58:38 -0500 https://reprap.org/forum/read.php?1,738012,738607#msg-738607 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738607#msg-738607

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o_lampe
I was wondering, if we could use optical mouse sensors as encoders?

They work on almost any surface and have a pretty good resolution. I could imagine, they are cheap too.
Just put such a sensor on your linear rail and let the 2020 profile be your encoder strip. B)-

That sounds like an excellent idea to me.

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o_lampe
Regarding suitable dc motors, we could look into car industry. There are tons of 12V motors in a luxury car. (eg. electric driver seat adjustment )
Might be, we find a suitable, mass produced geared and encoder-fitted motor for cheap.

My concern would be that most of those motors don't get a lot of use, so brush wear wouldn't be an issue in a car but would be in in a 3D printer.]]> dc42 General Sat, 14 Jan 2017 03:42:29 -0500 https://reprap.org/forum/read.php?1,738012,738599#msg-738599 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738599#msg-738599
They work on almost any surface and have a pretty good resolution. I could imagine, they are cheap too.
Just put such a sensor on your linear rail and let the 2020 profile be your encoder strip. B)-

Regarding suitable dc motors, we could look into car industry. There are tons of 12V motors in a luxury car. (eg. electric driver seat adjustment )
Might be, we find a suitable, mass produced geared and encoder-fitted motor for cheap.]]> o_lampe General Sat, 14 Jan 2017 03:28:51 -0500 https://reprap.org/forum/read.php?1,738012,738485#msg-738485 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738485#msg-738485 www.youtube.com] I think that is by misan? That demonstration seems to get quite far - it actually prints.

I would try to reproduce what he did, but I can't find a source for the motors he used. I think he has an additional Arduino mini driving each axis, so I would try to incorporate that function into a printer firmware. He has added the DC motors with minimal modification of the Prusa, adding an encoder strip would need more work.

I think firmware designed for shaft encoder would be easily transferable to an encoder strip, I think a single firmware should be able to support both with suitable parameters. I guess that handling 4 axis closed loop could be done with AVR arduino but would reduce top speed achievable, ARM would give more headroom.]]> bobc General Fri, 13 Jan 2017 12:47:20 -0500 https://reprap.org/forum/read.php?1,738012,738482#msg-738482 Re: 3-axis closed loop motion control https://reprap.org/forum/read.php?1,738012,738482#msg-738482 AleksClark General Fri, 13 Jan 2017 12:41:14 -0500