encoder issues

[rutexus]

Info on encoders:

The differential output encoders have two complementary wires for each channel. If one is logic high (5V), then the second output is logic low (0V). These encoders have 6 or 8 wires - depends if there is a index pulse or not. Index pulse is a one pulse per revolution ant it is usually used for homing or synchronizing more drives for one axis.. The R9xH boards do not use index pulse.

Single ended encoders have only one wire for each output. They have 4 or 5 wires (two for supply, one for A, one for B and one for I). Single encoders can be different type such as CMOS, TTL and OC (open collector). The difference is in amount of current they can sink and source - encoder output current and voltage for logic low and logic high.

The single ended CMOS can sink and source same current and voltage level is close to supply rails. They usually can sink/source in order of 10's of milliamps. They can be directly connected to R9xH

The single ended TTL can typically sink -24mA and source 4mA. The logic low is less than 0.5V and logic high is more then 2.4V. They need external pull-up resistor (about 470 ohms) for each channel for direct connection to R9xH boards. The pull-up resistor is a resistor connected between the output and +5V. In can be housed inside the DB9 connector shell.

The single ended OC can usually sink plenty of current (100mA+) but they cannot source any current. They again need pull up resistor.

Your encoders are OC (LM2901 is comparator with open collector with build in 1K pull-up) and they can be directly interfaced to R9xH board as long as the cable is very short. If you want to use long(er) encoder cable you should use board such as R516. This is a converter between CMOS/TTL/OC encoders to differential output. This R516 board should be mounted close to encoder and then you can run long cable between this board and R9xH board. With good quality shielded twisted pair cable you can run encoder cable for ten's even hundred's of meter.

Please feel free to edit and post above text on the CNCzone forum.

The delivery to Ontario is about 3-7 days by EMS or 5-10 days by Air Mail post. The shipping charges are listed at www.rutex.com. The weight of each board is about 0.2-0.4 kg.

vh

Subject: Re: r990h


Hi Vladimir, I got some more information on the renco encoders I will be using, The details are below. To clarify for myself, how do the single ended, open emitter and differential encoders differ from one another? Is that the same as absolute and incremantal types? If you get a chance I would greatly appreciate your help.

I guess I will go through the rutex web page to purchase the drives (r990h), What is the approx.delivery time to ontario canada? I assume there are shipping costs as well as brokerage fees/taxes?

Thanks again for your assistance

K. Challenger





RM15 = 1.53 inch diameter incremental modular encoder series

D = Channels A, B and Index

3 = Performance of 0 to 200 kHz and -10 to 100 degree C operation

500 = Resolution of 500 ppr in quadrature

¼ = Hub size of ¼ inch (.2498” to .2502” tolerance)

5 = +5VDC +/- 5% @ 135mA nominal

CS = 18 inch shielded round cable with termination of 4 inch leads, strip and tinned ¼ inch

VC = Voltage Comparator output interface (LM2901 with 1K ohm pullup resistor)

0 = Ungated index (360 degrees +/- 20%)

C4 = Non through shaft snap on cover, 1.812 mounting tabs using #4-40 X ¼ hex socket cap screws for mounting the encoder

S = Special non standard cable assembly.



This part is no longer in production and can be replaced with the RM15D3-500-1/4-5-CA18-VC-0-C4, RENCO P/N 77822-043. This unit is the same as the above unit except the cable assembly is our standard 18 inch length with termination using the AMP IDC connector P/N 103971-7.

[ynneb]

This is what Vlad sent me some time ago.
It works for my open end encoders.
This is how to wire up your Renco encoders.
Just leave out the Non inverse wires.

The limitation of open ended encoders is that you are limited in the distance of the cable you can run to them.

I note that Rutex also sells adapters that make your open end encoders to differential encoders. They sell them for $19.00

Pin#
Signal Name
Description
Renco - *CA18 encoder

1
+ 5V
Positive supply for encoder
RED

2
Ch – A (non inv.)
Encoder input channel A
WHITE

3
Ch – A (inv.)
Encored input channel A
YELLOW

4
Ch – B (non inv.)
Encoder input channel B
GREEN

5
Ch – B (inv.)
Encoder input channel B
BLUE

6
Shield
Cable screen
SHIELD

9
0V / signal ground
Supply for encoder
BLACK

[ynneb]

Thanks Rutexus for posting your corespondance here. I feel after a while you will build up quite a reference that you can point others to.

[DLMACHINE]

I'm all set to order my dervos and ran into a question.They are offered with 500 line and 2048 line encoders. Will the Rutex hardware work with either?

[ynneb]

I'm all set to order my dervos and ran into a question.They are offered with 500 line and 2048 line encoders. Will the Rutex hardware work with either?

Yes

[rutexus]

The drives will work with encoders of any number of lines. The number of lines, counts per revolution is immaterial to the drive. But the number of counts per second could be a limiting factor on your speed. The drive counts four times for each line of the encoder, so a 2000 line encoder would provide 8000 discrete positions for each turn of the motor. That is pretty high resolution. At 2000 RPM motor speed, the motor would turn 33.3 turns per second. Therefore a R990H drive would need to read 266,000 pulses each second. This is not a problem for a Rutex drive, but Mach 2 and most step and direction programs I am familar with can only provide step pulses at 45000 pulses per second. Ability System's indexer lpt can provide a smooth pulse train in excess of 100,000 pulses per second if this kind of resolution is needed. Hope this helps.

Tom Eldredge

[rutexus]

Following up on the last post, I might add that the Rutex R990H can handle encoder pulses in excess of 1,000,000 pulses per second. This means that an encoder could have as many as 8000 lines per revolution, giving 32,000 discrete positions for each rotation of the motor, and if that motor is rotating at 2000 rpm, the drive should be able to keep up with it. I would not want to try to pay for an 8000 line incrimental encoder however. I don't know who would make one. Around 2000 lines is the practical limit that I have found. A 2000 line encoder attached to a motor that drove a ball screw directly (not the best configuration) and a ball screw that turned 5 turns per inch would give you a resolution of a quarter of a thousandths of an inch. Thats all for now.

Tom

[kayakman]

Originally Posted by ynneb This is what Vlad sent me some time ago. It works for my open end encoders. This is how to wire up your Renco encoders. Just leave out the Non inverse wires. The limitation of open ended encoders is that you are limited in the distance of the cable you can run to them. I note that Rutex also sells adapters that make your open end encoders to differential encoders. They sell them for $19.00 Pin# Signal Name Description Renco - *CA18 encoder 1 + 5V Positive supply for encoder RED 2 Ch – A (non inv.) Encoder input channel A WHITE 3 Ch – A (inv.) Encored input channel A YELLOW 4 Ch – B (non inv.) Encoder input channel B GREEN 5 Ch – B (inv.) Encoder input channel B BLUE 6 Shield Cable screen SHIELD 9 0V / signal ground Supply for encoder BLACK

Does thsi count for all Renco encoders. I have a couple of motors that I´m about to connect to a R990 Rutex card but I dont know really what typ of encoders it is other than that it is renco 1000 CPR encoders. Are the differential encoders or open ended (TTL) ones?

Can I use the connection info that you have posted.

Best regards / Anders

[Al_The_Man]

You can either get the info from Renco or look at the number on the driver IC and Google the IC number and that should tell you the type.
Al.

[ynneb]

As I have said to you offline, you would be hard pressed to blow an encoder if wired incorrectly. ( I know this from experience) You should be pretty safe if you wire the Red and black as positve and negative to the encoder, and then follow the above directions.
It is either going to work or not work. You will know if it works because the servos will remain stationary and spring back to position if moved from thier point.

Just make sure the servos are not connected to driving your machine while you test them out ( Obviously )

Another tip...

I have found that the Rutex tuner is ok for tuning the servos while they are not connected to you machine, but when they are connected you will have to tweak them by hand/eye/feel.

[kayakman]

Originally Posted by ynneb As I have said to you offline, you would be hard pressed to blow an encoder if wired incorrectly. ( I know this from experience) You should be pretty safe if you wire the Red and black as positve and negative to the encoder, and then follow the above directions. It is either going to work or not work. You will know if it works because the servos will remain stationary and spring back to position if moved from thier point. Just make sure the servos are not connected to driving your machine while you test them out ( Obviously ) Another tip... I have found that the Rutex tuner is ok for tuning the servos while they are not connected to you machine, but when they are connected you will have to tweak them by hand/eye/feel.

Have tuned the cards now and have som equestions. The motor will turn exactly 1 turn if I move it 8000 steps in the Rutextune program. Does this mean that the encoders are 8000 steps per revolution?

Another question that I have is what are the main goal when tuning the drive?
Is it to minimize the overrun by adjusting the PID parameters or?

Shall I do this while trying to have as low P, I and D on the cards.
I got the motors to run with very little or no overrun and no oscilation when using the following values:

P = 2080
I = 0
D = 1312

No overrun and no Oscilation. is this ok and should I be satisfied with this values?

Another strange thing that I noticed is that when running the motors fast they run fine but when running them slowly they falter/chop one ime per revolution on the exact same position. I will test the other motors to see if they do the same. Any suggestions?

Best regards / Anders Molin

[rutexus]

Anders,

You want some overshoot in your tuning to make your drives snappy in their response. In the tuning process, there is no deceleration, so the drive should overshoot. When running a real time cnc operation there is always some deceleration to bring the mass of the machine to a smooth stop. During this decel time the drive will slow down and there will therefore be no overshoot.

Try to adjust the drive so that you have some ki in the final adjustment.

You definately want no oscilation. Even during tuning, keep it to a BARE minimum. Shut off the VM power almost instantly if it starts to oscillate wildly.

If your current trip value is too low, the drive may hesitate. Take the peak current specification of the motor and divide it by .2

That is the number you put into the current trip value.

Set the fall back current much lower so that if you ever ram into something after 2 seconds the drive will fall back to that current level and not fry the motor or blow the drive.

Tom Eldredge
Rutex LLC