Incrimental encoders for closed loop $$$

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a4x4kiwi
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Incrimental encoders for closed loop $$$

Post by a4x4kiwi »

Hi All,

I am after an incremental encoder for closed loop control of the Electro-Lux.

I have found the following from PCA

IPHJ series 785+GST with a 42mm hollow shaft to suit the motor output shaft. (IP65 rated, 500 PPR)

They also have INHJ-12HS-27AM-00500 with a 12mm hollow shaft (IP65 Rated 500PPR) for $625+GST which will fit the fan end of the motor if I have the shaft turned down.

The shaft fan is removed from the motor. I use an electric fan.

Has anyone come across anything else suitable and cheaper before I shell out?

Cheers, Mal.


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Squiggles
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Post by Squiggles »

What output signal(s) do you require?
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Johny
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Post by Johny »

The place where you got the Inductive pick-up have encoders.
This one needs an 8mm shaft but does 1000 PPR (Tuarn recommended min. 1000 PPR based on his research). $290.
Automation Direct Encoders
Just a thought...
Either turn the shaft down or drill and tap it and cut a thread on a piece of 9mm stock and screw it in (with Loctite). Then use the motor to "turn" the stock down to 8mm (or use 8mm stock if the misalignment due the thread is deemed OK). Shaft may already have a threaded hole.
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Post by Johny »

Hmmm. The ones I indicated probably have a terrible IP rating - mine is IP50. I have to make some protection for it soon.

Edit: Not IP21, IP50 for the one supplied with my motor. Minor point but best to be accurate.
Last edited by Johny on Tue, 19 Jan 2010, 10:24, edited 1 time in total.
a4x4kiwi
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Post by a4x4kiwi »

We really need IP65 or better. I also only have 40mm between the bearing and the electric fan on the front of the motor. It kind of narrows down my choices.

Mal
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a4x4kiwi
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Post by a4x4kiwi »

I forgot to mention, the danfoss input max frequency with a push pull driver is 65khz. This equates to 886 pulses per revolution at 4400rpm. The next lowest std ppm encoder is 512.

The type of encoder required is one with a quadrature output.

Regards, mal
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Squiggles
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Post by Squiggles »

What resolution do you need?
Can you fit a gear wheel/toothed pulley on the shaft?
Two inductive proximity sensors will give you the quadrature signal if places correctly. They can be had with good IP rating, from memory 8mm diameter ones.

http://www.oceancontrols.com.au/Sensors ... ensor.html

http://www.am.pepperl-fuchs.com/product ... up_id=1598

http://www.balluff.ca/Balluff/us/Produc ... r+Mini.htm
a4x4kiwi
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Post by a4x4kiwi »

I already have a proximity sensor on a toothed gear with a resolution of 40 pulses per revolution. Unfortunately this resolution is no good for using closed loop where you ideally need several hundred PPR. I have tried to run closed loop with this but the drives output is quite random.
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acmotor
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Post by acmotor »

I recently purchased one of these from RS components for $212 + GST.

Shaft Type Incremental; Miniature
Output Signal Push-Pull
Steps/Rev 1024
Pulse Per Revolution 1024
Supply Voltage 5 - 24V(dc)
Body Diameter 24mm
Switching Frequency Max 160kHz
Connection Pre-wired 2m cable
Maximum Revolutions 12000rpm
No Load Current 50mA
IP Rating Housing IP64

It is small.
I'm making and adaptor for it now.

I know the fin of the Danfoss is at least 120kHz in practice with push pull encoders. I ran a 4096ppr encoder to 4000RPM originally.
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Squiggles
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Post by Squiggles »

a4x4kiwi wrote: I already have a proximity sensor on a toothed gear with a resolution of 40 pulses per revolution. Unfortunately this resolution is no good for using closed loop where you ideally need several hundred PPR. I have tried to run closed loop with this but the drives output is quite random.


I can understand the need for several hundred PPR in a CNC machine where fine control is paramount, mind you with stepper drives the resolution is inherent. A bit surprised it is required in a traction drive. What makes it necessary?
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Post by Tritium_James »

The controller needs a fast update rate on an accurate velocity measurement, so that it can control slip angle properly.
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Post by Squiggles »

How do controllers that use BEMF measurement manage it?

Thinks....BEMF proportional to slip maybe....so high resolution ADC....
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Post by acmotor »

Answer is, not very well.

I think you will find all VFDs cannot provide full torque from zero RPM in the sensorless (BEMF) control mode (no rotation = unclear picture of what is going on). (even though sensorless control from say 100RPM is fully torqued).
An encoder is required and there needs to be 1000ppr or so to make the control loop work smoothly. Ive tried 8ppr and Mal has 40ppr, just not enough. Control loop goes loopy ! Danfoss text etc. suggest 1000 to 2000 ppr for an encoder.

I find the Danfoss VLT5042 can supply 170% nominal torque from zero in sensorless mode unless you lock the v/f at low revs (use 'special' speed mode).
With an encoder fitted (I/ve run a 4096 previously) the torque can be wound up to pullout 300%+ (or just below preferably !)
In speed mode there are still kangaroos in the control loop if you apply full torque with the brakes on. Thus encoder required.
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Post by Squiggles »

So what you are really saying is that DC is much easier Image
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Post by woody »

Does the surplus place you got your motor originally from have encoders?
RS had some hollow shaft encoders for about $500.
ABB wanted about $1600 for fitting one to a new motor :-(
have you tried putting your current encoder through a PLL circuit or similar which outputs 25 pulses for every 1 real pulse input?
Can you get a 500 or 1000 pulse wheel laser cut or even use a circular PCB with your existing pickup?
(more crazy ideas)
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Post by Squiggles »

Last edited by Squiggles on Tue, 19 Jan 2010, 18:04, edited 1 time in total.
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Post by a4x4kiwi »

Thanks all for your suggestions. Keep them coming. For ease of implementation I will probably go for one of the products from PCA.
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acmotor
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Post by acmotor »

Squiggles wrote: So what you are really saying is that DC is much easier Image


Yep, the encoder runs off DC. Image

Oh, you mean thongs are simpler than ABS. Image
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acmotor
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Post by acmotor »

Hey Mal, does that mean you've rewound the motor ?
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a4x4kiwi
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Post by a4x4kiwi »

Not yet Ac.

When I pull the rotor out to machine the fan end of the shaft for the encoder, I will check if the windings are accessible enough to hack to 200v star.

I recall some time ago that the Danfoss tech helped with your PID parameters. Do you have any advice in setting up closed loop.
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Post by acmotor »

Yeah, Danfoss were helpful.

Closed loop speed was little different to open loop except more torque (and smoother) from zero speed. Gain was reduced to the minimum (0.04? units?) so it was not trying too hard to hold speed but integral was doubled from default to accumulate demand when load was high as the gain was low. Derivative was off since you were chasing a loose control for EV operation i.e. not twitchy on the accelerator.

Torque mode with encoder was the most impressive (nearly took out the garage door !) although I haven't established a negative torque application method (brake pedal etc) yet.

Did you resolve the earth leak problem ? or does it go away in summer ?
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Post by a4x4kiwi »

Thanks for the info. The experience of those that have gone before is invaluable.

The Earth Fault has gone away. The only thing I have found to 'fix' is to tighten the heads of the contractors as they were all loose. Since I tightened them I haven't had any problems. I also found the at the pre-charge contractor does not always pull completely in.

Its a bit of a stretch that the contactors would cause the earth fault, and not fail under full load, but I am happy it is working!
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Post by bga »

Hi All, I was looking at a KOYO encoder from World Encoder
Here

I thought these to look suitable for the duty - the size 15 solid shaft.
List price USD132+
The metric solid shaft types are even cheaper.


I would want IP66 at least.

Cheers
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Post by acmotor »

a4x4kiwi wrote: ..........
The Earth Fault has gone away. The only thing I have found to 'fix' is to tighten the heads of the contractors as they were all loose. Since I tightened them I haven't had any problems. I also found the at the pre-charge contractor does not always pull completely in..........


Or maybe it is just summer ?
What is with the heads on the 'contractors'.... you mean contactors !

That precharge contactor in most VFDs is a small 3 phase contactor with contacts in parallel to roughly share current. It is on one side of the DC bus only so any contact faults could cause an unbalance.

Interesting encoders bga.

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Post by a4x4kiwi »

OK. Time for a bit of an update.

I have bought an encoder, and will be turning down the shaft this afternoon.
As I have never been able to post photos here, I have p[ut some on my blog.

http://a4x4kiwi.blogspot.com/2010/02/mo ... ambly.html

Cheers, Mal.
Silicon is just sand with attitude.

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