RV4s - please post

[Teuneman]

Hi guys,

We have a couple of RV4's machines that have given flawless service throughout the years but we are now picking up a problem on one machine.

Basically this is what happens:-

When the machine picks a part from a feeder it does not lift up the part completely in the z direction or the nozzle does not latch in the up position. This causes the nozzle tip to crash into the top plate of the feeder as the arm is moving in the x-y direction. This problem occurs very rarely and is intermittent ie 2000-5000 component placements no problem then the crash. We have replaced the 'o' rings on the nozzle spigot as we found them to be different sizes or the middle 'o' ring had simply worn down. We understand that this is a common problem with these machines. We are thinking that it is either:-

a)      Faulty stepper motor
b)      Faulty wiring in the arm
c)       Worn cam on z-axis mirror
d)      Faulty bearing that rides on the cam

We have checked c and can't see any problem and d seems to run ok. Any ideas on what the problem could be?

Regards

[Mike]

Certainly sounds like the Z axis slippiing - as it happens so infrequently it seems unlikely to be a dodgy motor or  a mechanical problem - wiring or connections seem most likely to fail due to flexing and vibration over a long period.

On the basis of likelihood and ease of repair, I'd be inclined to check or just replace the connectors on the vertical axis stepper. At least try repeatedly running the head up & down while pulliing & flexing the wiring wherever you can get at it. Check it all the way from the motor, right back to the control box, and then back  to the PC.   

I'm told that some older units with toridal transformers instead of switchmode PSUs can have occasional problems, especially at low line voltages.

[Teuneman]

The machine worked great for a couple of days now. And then it happned... This time I saw EXACTLY what happned. The head goes down to pick the part and it seems as though it is "looking" for the part way lower than where I set the bias. It's not slipping, it's actually moving there. So I'm thinking software related?

[Gopher]

I've seen mine do something like you describe a few times; but not quite the same. I'd guess @ number 2, the only difference between what your describing and what happened here is yours seems gradual (which makes more sense), whereas mine went from perfectly ok to can't even place 20 parts in the space of a day.

1)The machine would seemingly lose track of its head and try to pick ahead of the pick position, and if left trying the remaining positions would crash into to its own arm column as well as potentially scratching your pcb and other bits of chaos. Accompanied very horrendous crunching noises and requiring an emergency stop followed by manually parking the head. Usually took about 1/2 day running time to happen which was the basis for thinking overheating. For us this happened mid summer when it was 3? years old. VSMT took it away and found a sightly bent plate somewhere but said this was more likely caused by the fault rather than being the cause, however they also placed 5k parts and didn't see the problem. I went out on a limb and have since run the machine with the door open to the cabinet underneath and pointed a deskfan through it, its never happened again.

2)Placement accuracy and pick get progressively worse before completely failing: The head moves up and down a rack and pinion, this had become work so bits were moving, just enough for the machine to not really know where it was.

3)Random fails, crashes, and odd behaviour including placement: A faulty RAM module! If only all faults were this easy. Didn't even call VSMT for this one.

[Teuneman]

Thanks for the info.

1. Horrendous is a good way to describe it. I don't think overheating is my problem. I had this in winter too. I have aircon in the room and ambient is usually about 20 C. I also leave the cabinet door open. (just haven't tried the fan yet.)

2. There is some play on the rack and pinion but not noticably more than my other machines.

3. It could be memory,  had a faulty capacitor on the motherboard a while back and repaired that. Maybe it could have caused other problems.

I think you're helping me into the right direction thanks.

T