Advice Needed, Converting a Boxford VMC 190

[m_c]

1) This depends on 2) combined with pitch of screws, any gearing between motor and screw, and if you're setting up in metric or imperial.

Essentially, most common stepper motors are 200 steps per revolution, so multiply that by your answer to 2) to get your steps per motor revolution. If there is gearing between the motor and screw, you then need to add that into your equation to get number of steps per turn of the screw. You then need to divide the steps per screw turn, by the pitch of your screw to get your steps per unit. Your unit will be either 1mm for metric, or 1 inch for imperial.
i.e. 200 x 8 = 1600 steps per motor rev. I'm going to assume you're motors will be direct connected to the screws, so you still have 1600 steps per screw turn.
Assuming metric and a 4mm pitch screw, you then divide the 1600 by 4mm to get 400 steps per unit.

2) 8 is usually best the compromise. Any more doesn't gain you any accuracy with a stepper system, and less can make things a bit jerky at low speeds, although it may be needed if your step pulse isn't high enough to get reasonable speeds.

3) How fast is your bit of string? Generic guidance is keep upping the figures until things start stalling, then back of a bit to provide some saftey margin.

4) Depends on how many wires the sensors have. 3 or 4 wire, are easily useable provided thier voltage range is useable. 2 wire, bin them and buy new, as they'll be NAMUR output which interfaces will cost you more than new sensors.

[Marv2097]

Thanks m_c,


I am currently set to 16 on the drivers and it runs fine but will change this to 8 and see how it goes.

The X and Y motors are directly connected but the Z has a toothed belt, It seems to be a 1:1 ration so should be fine. I think i need to measure the pitch of the screws then I can calculate the steps as you described.

The sensors are the 3 wire type and are 10-36vdc so I will get one hooked up to some power and see what the output wire does when it reaches home.

[m_c]

If you get enough speed at 16 microsteps, then there's not really any need to change it. One thing to consider, is microsteps should never be relied on for accuracy, as the stepper position can only be guaranteed to the nearest step. While microstepping, both coils are proportionally energised, with the rotor essentially held between two magnetic fields, so can spring/float (there probably is a better word, but I'm tired!) depending on load.

Sensers will most likely be NPN with an open collector. Are there any numbers on them?
If there is, try googling it to see if there are any datasheets for them, which will confirm what they are.

[m100]

This post mentions a wiring diagram for the Boxford 190. No reponse to a PM and the user hasn't posted for quite a while.

Interested if someone can supply a wiring diagram to aid conversion of my 190 (Lenze controller type)

[Edvard_acz]

Thanks m_c
All the explanation was awesome :)