Incrimental encoders for closed loop $$$

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.

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.

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

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/ibest/hall_effect_sensor.html

http://www.am.pepperl-fuchs.com/products/productgroup.jsp?division=null&productgroup_id=1598

http://www.balluff.ca/Balluff/us/ProductsChannel/Overview/en/Inductive+Sensors+Tubular+Mini.htm

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.

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

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.

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)

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

Hey Mal, does that mean you've rewound the motor ?

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 ?

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

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/motor-dissambly.html

Cheers, Mal.