5 Attachment(s)
Anatomy of the Z Encoder 101
Here we go again AL digging into the Carve Machine.... At 444 hours this morning the Z stalled and after reset dove into the wood or it looked like it did... Stalling on a down stroke...
Started this in AL's Gloat at post 80 something..... Moved it here.
Troubleshooting this problem it is looking more like a Bearing failure as the clicking in the bearing, and when the bit flag is out and the head is going down it stops in mid air 1 inch from the bit flag.....Twice..... Re booted and it did the same 3 times in a row between boots. At the bit flag it is looking for the touch to the bit plate by monitoring the motor current. A increase in current = a touch.... Stopping mid air.... Bad bearing I think.... I have bearings so after I talk to LHR I think that is next. The 3rd clue was the line on the board between carve areas, the Z should have gone up and over but it didn't.. Stalling below depth.....
SO...... I took the Z motor apart looking for the problem but it looks good.
The disk in the picture has magnetic bars or lines on it and as the disk is rotated it is like a baseball card in the spokes of a bicycle tire. Click, click, click.... That is how the motor tells the computer it is working. In this type encoder it is just clicks after it finds home position it resets the counter and all movement after that is either positive or negative pulses from home position. The other style encoder is called an Absolute Encoder where actual number data is on the disk and it always knows where it is on power up based on the wheel data. It never needs to seek home. Fanuc Robots I worked with at Sony used them.
SO..... Here are some pretty pictures of the Z.... And a replacement Encoder Board. One was in the bottom of the box when I sent my Z pack in for repair.... It just solders to the motor power wires.
A close inspection of the circuit board will show the tiny copper solder pads for the pins of the plug supplying the power and taking back the Encoder data. History shows that the area where the pad ends and the very fine circuit board conductor leaves the pad is pron to failure in the forum of stress cracks. The crack in the copper trace will cause failure of the computer to know where the Z is causing the Diving into the board some of us remember.
Enjoy the pictures..... Great picture of the morning sun shinning through the disk showing the magnetic markings....
AL
I'm not so sure that's a magnetic encoder. It may be optical.
Quote:
Originally Posted by
Digitalwoodshop
Bump.........
I realize I'm coming to the party a little late but after viewing the photos I'd say it's an optical encoder. I could not see a part number on the thing to find out what model and who made it? I'd love to hack one of these someday! That black thing the disk revolves in probably has an L.E.D.(light emitting diode) in it that shines light through the disk and a photo resistor on the other side of the disk. Usually set up in pairs out of phase from one another. The photo resistor varies it's resistance by the amount of light being shown on it's surface. The printed bands on the disk break up the light beam being shown on the photo resistor and thus we are able to count R.P.M.'s and determine location by counting how many light blinks or variances in resistance from the photo resistor have transpired. With the photo resistors in pairs and out of phase helps determine the direction the motor is spinning.
If anybody has one of these encoders apart there may be a product number or manufacturer name on the black plastic housing somewhere.
I did a product search using the numbers on the circuit board but came up empty handed. The only encoder sold separately is kind of in the board sensor assembly and it's $35 bucks at the time of this writing. Too much money for me to order one just to play with. It may or may not be the same as the ones installed on the other axis I don't know. Encoders come in all sizes and flavors depending on your needs. Lines per inch (lpi) sometimes listed as pulses per revolution (ppr) is just one of the things that come into play when your trying to make things accurate and hopefully fast too.
