Hitachi wj200 vfd controls on a lht-25b turret lathe

I'm installing an Hitachi WJ200-015 VFD on a small turret lathe a LHT-25b (Lin Huan variety).


This lathe has a threading feature that I would like to use. I have not used this lathe, or any turret lathe for that matter, so my information is from the manual and looking at the machine.
If I use incorrect terminology for the machine functions that’s why.

The lathe has two momentary contact switches for FORWARD and REVERSE as the turret is cycled through the threading station.

The vfd has what seems to be common to most vfds’, an ability to use a 3 wire interface or 2 wire via 7 logic inputs.

Logic is 24vdc with 100mA

Using the 2 wire logic inputs they require Maintained Contact switches for forward, reverse.

Using the 3 wire the stop is maintained and the start is momentary and forward/reverse maintained.
I can only use a 3 wire or a 2 wire not both.

The following is from an email conversation with an Hitachi tech (his reply italicized)

“I have three questions concerning switches to the intelligent inputs,

1. Can I use momentary switches or must they be constant contact type. If yes, is there a parameter change?
If you use the inputs as RUN forward and RUN reverse, they are maintained. If you use the inputs as START/STOP the stop is maintained and the start is momentary. Each input can be programed individually.

2. Can I use both a three wire configuration and the other logic inputs having a forward, reverse type inputs?
You must use either 2 wire or three wire configuration. You cannot use them at the same time.

3. I'm installing this on a turret lathe with an existing threading feature, this uses two switches. When in use when selecting the threading tool it contacts a switch causing the spindle to turn forward when a prescribed depth is reached it contacts another switch sending the spindle in reverse. Using this VFD can I go directly from a forward condition to a reverse condition without a stop command?
When the drive transitions from a RUN forward to RUN reverse, it will decelerate at the deceleration rate programmed in parameter F003, after reaching 0Hz, the drive will starting running in reverse.”

The problem is this, the threading contacts are momentary and the forward/reverse logic inputs on the vfd require the switch to be maintained with a STOP action between state changes. The vfd will stop if it receives both a forward and reverse input simultaneously.
So, I need a main control for forward and reverse and the threading switches for forward and reverse how do I achieve this with the vfd?

Original wiring schematic.

Threading fixture from a Valuemaster lht-25b (not my machine but principally the same)

I believe I've worked up a solution using the three wire interface and a relay arrangement on the turret limit switch and the for/rev switch, I'll check it out in a few days.

Use either mechanical relays or a programmable relay with dry contacts to build 2 '3' wire equivalents. Then either Run Forward or Run Reverse. It shouldn't cost more than $100 in parts either way.

My lazy 2¢

How are you going to be threading? Are you going to use a releasing tap/die holder, or a self-opening type? If so, OK. But if you want to use a solid holder, and reverse the lathe at the proper thread depth, that might be problematic.

What I am seeing here is that the original threading setup sounds like it does a "plug reverse" to get a fast reverse on the motor. That presumably reverses fast enough that it does not turn very many turns after the reverse is started, before it is reversed. Plug reversing is basically slamming it in reverse, and draws a lot of current, actually more than a start from stopped condition.

What the Hitachi guy is saying is that the VFD cannot do that, it has current limits, and so it has to gradually slow down before it starts in reverse. Where the "plug reverse" might stop and reverse in just a spindle turn, or possibly less, the VFD may take 5 or more turns. When threading, that can be significant.

If you can predict it, or test it, so that you know how much that will overshoot the intended stopping point of the thread, you can compensate for it, But I am not sure you can count on it within one turn, you probably will have a couple turns of variance.

It seems more practical to find a releasing tap/die holder or self opening threading tool so that you can fairly precisely set the point at which the thread ends. Then either the reversing is non-critical, or you can avoid reversing at all (self-opening holder)

Are you SURE the motor isn't a brake motor??

threading relay circuit

This is the circuit I've come up with. It's wired parallel to the F/R of the 3 wire interface.

It works so far in a soft install on the new motor (still doing some clean up and haven't installed the motor yet) it seems pretty simple, simple enough for me to wonder what I'm missing.

There is a difference in wording between the user quick guide and the manual regarding the logic using the 3 wire interface, one states ON (high)= FWD, the other states ON selects reverse direction while OFF is forward. I suppose this could simply be looked at as ON goes one way while OFF goes the other.
For my purposes I wanted the relay to be ON when reversing and OFF when in normal "forward" operation, it worked out that way for me, but this may be problematic due to motor orientation in another machine.

This uses the +24 on the vfd, the jumper wire is PLC to L, the (-) on the relay coil is connected to L on the vfd and not chassis ground, this may be obvious to most but for me it took a minute. Isolated transformer.
Appreciate the responses. I hope this helps the many thousands that are attempting to wire a vfd to a lht-25b turret lathe.

Interesting lathe, I build control system and use proximity sensors on lathes for limit switches as opposed to mechanical.

The schematic looks ok, although I often use 2 wire configuration with two latching relays with momentary switches for direction and stop, the direction switches/relays are cross wired so only one direction is active at any time. You do not need to hit stop to reverse the system. My questions on the schematic you have is what stops the system after the reverse is engaged and the cutter moves back to it's starting point and the latch is broken. As drawn the cutter would cycle back and forth until you hit the stop. I assume there is some form of indexing system to move the cutter away after each pass. Also you would need P24 going to the front control panel, it is missing in you schematic and assume F/W is F/R which would be a sustained front panel switch, and if this was ON for a left hand thread the reverse limit switch would not work. It is possible to take this into account, but more complicated. The VFD L/PLC are isolated from the VFD ground, the WJ200 terminal power supply is limited to 100mA, so one needs to choose a relay that draws less than this. Multiple relays requires an external power supply.

Using 3 wire, the reverse is usually a sustained closed contact (although inputs can be programmed as NC or NO). You can set the braking speed to different rates, so I normally program 1 second braking for threading operations and have a switch to select 2 stage for other operations.