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Solution for a stable RPM from a DC motor

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HiQ

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DC MOTOR RPM CONTROL

last year while working on a project I needed absolutely stable RPM from a DC motor. I came up with a solution that is simple and worked verry good. Is there a list of other solutions that i can go trough in order to find out weather I invented something new? :?:
 

Re: DC MOTOR RPM CONTROL

One method is to occasionally remove the power and measure the back emf. Another way is to measure the shaft speed in the classical servo method.
 

Re: DC MOTOR RPM CONTROL

It is none of those that you mentioned. there is something atached to the shaft for feedback to the PWM and a adjustable frequency generator that "locks" the RPM to those desired by the user.
 

Re: DC MOTOR RPM CONTROL

If i uderstand correctly you are using an encoder to determine the speed of the motor, i am working with this devices at the moment, is quiet simple to use, once you have a frecuency you can use a control block to determine the correction to the PWM, is just a feedback control system.
 

Re: DC MOTOR RPM CONTROL

I'm not familiar with you're system. What i do is generate a freq. that i need ,for example 15 Hz for 900 rpm. At each rotation the PWM is adjusted to make sure that even under varying
load the RPM is constant.
 

DC MOTOR RPM CONTROL

I do not understand how your system works. Mind to share more ?
 

Re: DC MOTOR RPM CONTROL

The freq. gen. creates a pulse (for example) each 66 ms. that prompts the sensor to scan for a marker on the rotor. If they "meet" where they should, the power is left unchanged. If the marker lags behind or has completed the revolution in less than 66 ms the feedback automatically adjusts the PWM. This is done each revolution to make sure the marker on the rotor is "locked in" with the freq. gen. It's actually very simple & can be added to any existing setup.
 

DC MOTOR RPM CONTROL

Interesting ...

Therefore, you can adjust the frequency of the frequency generator (FG) to 'set' the motor speed that you wish, am I correct?


[Newly Added]
If my statement above is correct ...
Let's say the frequency of FG is 100Hz and the speed of the motor is 100 rev/second. Assume that there is only one pair of sensor/marker in your system, so the motor can be considered to rotate at 100Hz (100 revolution per second).
Let's say now we wish to set the motor speed to 50 rev/second. So, we adjust the frequency of the FG to 50Hz. After a short instant the frequency is set to 50Hz, the motor speed should still remain at 100 rev/second. As 100Hz is an integer multiple of 50Hz ('harmonic'), the controller will still receive a 'matched' signal every time it promts to update the sensor/marker signal. Consequently, the controller will not update the PWM duty cycle and therefore, the motor speed will remain at 100 rev/second.
How do you adjust the frequency? Manually (using knob)?

[Newly Added]
However, it will not be so lucky to get both signals (frequency and sensor/marker) matched after the frequency is set to 50Hz. So, your system will still be working.

In my opinion, it's kind of conventional method used in OLD day to control the speed of the motor. In modern day, microcontroller is used to calculate the motor speed based on the sensor/marker signal (or opto-slotted disk). One of the advantages to use microcontroller is probably you can include kind of control algorithm (e.g. PI controller) to improve the response of the motor. However, if your application does not need fast response, then this advantage might not sound great to you.

Please update us ...
 

Re: DC MOTOR RPM CONTROL

I don't want to reveal it here. It could be old technique but i doubt it. It is analog, very simple & very responsive. the freq.gener. is kind of like "big brother" to the rotor. I use a motor from the radiator fan from a "lada"(russian car) and a (modified) impulse power supply from a computer.
 

DC MOTOR RPM CONTROL

If you think that your idea/product is novel, you may consider to patent it. Find more info from the following websites:

[url]https://www.uspto.gov/[/url]
[url]https://www.wipo.int/[/url]

Before you continue, you really need to review other people works, especially the benefits of your system compared to others. In many times, especially young inventors, always think that they have invented something new. Actually they don't have much knowledge (less literature reviews) in the area and 'their invention' is just new to them, but not to the world. Another situation is sometimes he/she feels reluctant to accept newer technology and claiming that what he/she knows is simpler and other are more complex. In fact, if he/she's willing to pick up the new knowledge, he/she might find out that the new technology will offer more and probably could further enhance or improve his/her invention.
 

Re: DC MOTOR RPM CONTROL

I think your system is slow in response. Because you are waiting one(or a bit more) revolution to compensate the speed error. And until you reach the desired speed, a lot of time passes. Also i wonder how do you adjust the speed. I mean if the motor is slow than you expected than you need to increase the duty cycle. But how do you decide how much you'll increase it? Conventionally PID regulator is used in this situation. How did you regulate the duty cycle?
 

Re: DC MOTOR RPM CONTROL

It seems that you have dedigned a mechanical PLL . This is a commun design to control the MOTOR SPEED on a DC motor
The motor ACTING as a VCO ( voltage to turns here or frequency )The comparator ..for the mark is the clasical comparator of phase in a PLL ...
of course the more marks you have the faster the lock-in time ..
 

Re: DC MOTOR RPM CONTROL

This subject generated more interest than I expected. Even if my system is new I don't want to bother with a patent(too expensive) I guess if you saw my product you could figure out what motor control I used ,but I don't know if it's OK to publish a web site here.
 

DC MOTOR RPM CONTROL

I believe it's a great invention. It will be our great honor to see it if HiQ could publish his invention at EDABOARD forum. Just a snapshot of your system is enough. No need a web site, I think.
 

Re: DC MOTOR RPM CONTROL

4get it then.
 

Re: DC MOTOR RPM CONTROL

8) I feel it is a good idea, what you have done is put a crude single point encoder kind of thing on your motor.
 

Re: DC MOTOR RPM CONTROL

I think any closed loop control system has to fulfil the following:-
1-zero "perfect" steady state error
2-fast responce
3-wide range of operation and disturbance compensation
4-its cost also should be not so high
5-the controllability of its paramaters
ur system uses a pulse as an observer,while it seems uses digital comparators like PLL,which is a perfect control technique for DC motor,mention on M.Rasheed power electronics reference.
Try to fufil the above operation parameters within ur mathematical model of ur control system
 

Re: DC MOTOR RPM CONTROL

I don't understand you're terminology much. imagine you place a arrow (sideways)on a turntable. each time you open you're eyes (prompted by the generator pulse) you see the middle of the arrow. If on the next revolution you "see" any other part (wider or narrower)it means the speed has deviated and you compensate the PWM accordingly. At first i used an optron hooked to a PIC that sent out either 4 volts to the motor if the revolution was done in less then 66 ms.or 6 volts if it was done slower. It worked but was not smooth enough for my project.
 

Re: DC MOTOR RPM CONTROL

Aha,
the sampling time is a very important parameter to control system responce and stability too.
i understood ur turntable example,it is exactly like u put a sampler in the feed-back branch in a digital control system,with a certain sampler frequency,but,seems that u use a wide pulses instead.
the smoothness comes form the high system resolution and stability within the whole range,this means the processing components "PIC as u mentioned "should be programmed to save time and take as fast responce
or action as possible.
The motor inertia,friction & load all take part in the time responce and stability of the system
i appertiate ur interest in the improvement of control systems espeacially on motors.
 

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