Yaskawa V1000 VFD for the spindle

Been away visiting family over Easter weekend, so nothing done between Friday morning and this (Monday) afternoon.

Next job is to install the spindle VFD. It's a 2.2/3kW V1000 (open loop vector control, rated for single phase / 200V Class operation). As well as wiring in the AC input and output, there is a "digital operator" (remote display panel) and a signals cable that will allow the CNC controller to turn the spindle on and off as well as set the speed. 

When I bought this last year, I ordered the braking resistor, the "remote digital operator" and the RFI filter. The latter is actually made by Schaffner, so I expected a bit of a Rolls Royce part that should work. However, I was surprised at the size of the thing. After a while the penny dropped - the 4 threaded inserts on the corners of the filter box are positioned to line up with the feet of the VFD. Furthermore, the preterminated output wires from the filter are the correct length to drop onto the input terminals of the VFD. And there are 2 further holes that are the correct pitch for the braking resistor mounting holes. There didn't seem to be any mention of how it is all supposed to be assembled but I seem to have figured it out one way or the other.

it's very nicely made and the various covers simply snap on and off to give access to the terminals. That extends to the fan assembly (easily swapped out as a serviceable item) and the main housing for the PCBA etc. 

I drilled and tapped some M5 holes in the rear of the machine, away from the swarf and coolant. I should probably fit a dust cover over the top, as it's really intended to be mounted inside a cabinet.

There it is. Not the prettiest installation I've ever done but I'm trying to be sensible / pragmatic about this rather than create a showcase professional installation.

In the high range, the spindle was originally specified for 6000rpm but it's possible it may be good for a bit more. It's not entirely clear what the rating of the old Hitachi VFD was but judging by the nameplate figures, it wasn't much different to this - peak shaft power seems to be about 3.2kW at base speed. The old VFD mentioned 5.5kW but I believe this was the peak input power whereas the Yaskawa arrived with a default setting of 3kW for the motor (shaft) power setting.

The Hitachi motor is designed for variable speed operation (rather than fixed speed with a gearbox or variator), although from the nameplate its base speed is 1760rpm at 60Hz and 190V. Clearly it must be entering field weakened region at reduced power when above ~2200rpm or so. That's how the original VFD worked in the old system, so it should be good enough for the likes of me.

These Yaskawa drives are proper industrial things and have parameters to suit almost any possible application. That makes them very versatile / powerful but also means there are loads of possible parameters to get busy with. The quick start guide that comes with the drive only summarises the key parameters and isn't much use unless you are already familiar with setting these drives up. The full technical manual covers everything but it's somewhat more substantial at 510 pages.

Once wired up, the setup procedure is:

• Enter the nameplate parameters (base speed, rated power, phase current, number of poles etc). You have to start out using base speed, rather than max speed if your motor has an extended operating speed range.
• Set the control scheme (open loop vector here).
• Run autotune (runs the motor and analyses / sets the key parameters).
• Increase the max frequency, if the motor needs to operate beyond the normal base frequency (200Hz in this case gives 6000rpm and reproduces the original speed range).
• Fiddle with parameters like accel / decl times etc.

As you might expect from Yaskawa, this proceeded fairly seamlessly once I understood the menu structure. The motor and spindle sound pretty good, which is handy given that I've just replaced the bearings. Mind you, with the spindle running at 6000rpm, you wouldn't want anything to come flying off at you. The VFD switching noise is certainly a lot less obtrusive with the new VFD. It's possible to select or define the switching frequency, so on the face of it, it would be possible to raise the frequency above audible (for old gits at the very least). However, if you double the switching frequency, you double the switching losses, resulting in a lower allowable load current. If anything, this VFD may be a little underpowered, as I originally specified it for converting my Bridgeport clone to CNC, so I don't want to lose any capability. TBH, the acoustic noise levels are pretty reasonable with the "heavy duty" settings I've set.

The motor and spindle combined have a sizeable moment of inertia, so there is a lot of energy to dissipate during deceleration. So it was easy enough to check that the braking resistor is connected up and working. After 10 starts and stops, it was beginning to warm up nicely. The achievable deceleration time seems to be about 2 seconds from 6000rpm, which doesn't sound unreasonable. I tried to get it down to 1.5s and it overvolted, so clearly I've found the limit - without any sizable tool fitted.

The spindle bearings were cool to touch after 10 min or so at full speed. That's sort of reassuring, given that I've just spent a fair bit of time and money replacing them. The bearing that supports the driven pulley above the spindle (and drives the spindle or backgear) was getting a bit warm, so I may need to replace those bearings too....

The other thing I did before attacking the VFD was to shorten the "CN3" cable. This contains the limit switch inputs as well as the various VFD control lines. As with the other cables supplied, it comes in at 3m overall. I'd already shortened the other cables so there wasn't much point delaying on this one. Sounds simple enough but it's a bit of a PITA swapping over all the ident labels and fitting new forked crimps - took the best part of an hour by the time I'd marked up the old connections, reworked the cable and refitted it.