Proximity sensors , Whats the deal ??

[JohnCo]

I have this new Chinese machine and it has a proximity sensor on one end only on each axis. Is this the way it should be is done ? There are no other type of limit switches anywhere on the machine . Is this how large machine are ? Or should I fit some limit switches?
My small machine had limit switches at both ends of all the axis.

[wildwestpat]

Hi JohnCo

You say that each axis has one proximity switch at one end of each axis. This implies that the switch is there for homing the axis. Depending upon the software used to drive the machine it should be possible to rearrange the switch to act as both homing and limit switch. Re-locate the switch to the side of the axis and arrange sensing blocks to protrude so that they pass the sensing face of the switch. One block at each end of travel. One neat way is to arrange for fixed sensing blocks to limit the travel and movable blocks to reduce the travel for small jobs. This saves the machine travel to the end of axis to home. However please note that these switches are not normally designed to act as mechanical stops despite their apparent robust construction.

The use of electronic proximity switches is begining to extend down to more modest machines as the cost has reduced a lot over the last couple of years. Currently £6GBP will get you a good quality electronic switch where as a sealed microswitch with a roller lever is the same price and a fully encased model arround £30GBP for the microswitch and housing. If properly set up the accuracy and reliability will exceed that of the mechanical switch. Depending upon the type of electronic switch - optical - magnetic - inductive - capacitative - the switch will offer advantages over those of a mechanical switch in addition to being fully waterproof.

If the new machine is fitted with servos not steppers and has no electronic protection for motor overload then it migh be worth considering safety switches at the end of travel just before the axis hits the buffers. This would help protect the motors from burn out. Not necessary for steppers.

Hope this sets your mind at rest and you enjoy your new machine to the full.

Regards

Pat

[JohnCo]

Ok Pat thanks for that . They are Steppers . I have the switches wired up as homing and limit switches.
I will give it some thought about either leaving the machine as is or whether or not to fit limit switches.

Thanks for the quick reply.

Regards John

[mactec54]

Most of the time when one switch is used, it will be a homing switch, once you have homed the machine, That will set up the soft limits in the control & you don't need any hard limits when you have this

A easy test is to home the machine & then run one axes slow to the other end were there is no switch & it should stop before you get to the end

Check your software as well they must have this information some were

You must always home the machine after each shut down for the soft limits to work

[wildwestpat]

Hi John

Unless you have the multi sensing block arrangement Mach3 will be configured with a homing switch - your electronic proximity sensor. The limits on travel will be set in the Mach3 software as movement from that home switch position. I expect that is what you are thinking but the terminology gets a bit fuzzy when the home switch is at the end of the travel.

Good luck and enjoy your new machine.

Reagrds

Pat

[JohnCo]

Iam using Mach 3. Is it that you set up the homing of the X axis and somewhere put in, that the table has a 1800mm cut and Mach 3 will not let the machine travel more than that from home?

Would someone have a couple of screen shots of mach 3 to show me where that is set up ?

[mactec54]

Did the Mach3 come with the machine already set up or have you done this, if it came already set up then most likely the soft limits are already done

A easy test as what I said in the last post move one axes slowly to the end of it's travel & see if it stops just before it gets to the end

[wildwestpat]

Hi
There is a good description in the Mach3 install and configuration set up guide - download from:-

http://www.machsupport.com/docs/Mach...all_Config.pdf

The section you want is 5.6.1.3 page 88. This has screen shot and covers in detail how to set it and how it works.

Good point about homing from Mactec54. The use of the single home at axis limit is fully covered in the configuration guide and in the user manual. If the manual that came with the machine is not easy to follow can I suggest you down load the other Mach3 docs. In particular with a new machine the calibration of the axis should be checked. Assume you have also checked that the axis are correctly set to 90 degrees to each other. A tedious check but worth while if there is any come back on the supplier the sooner it is identified the stronger your case for remedial action. Include spindle run out and axis backlash although it would be dissapointing if these were out of spec as even the low end bench tops are being turned out well set up these days apart from the odd sample that possibly got bashed in transit.

Enjoy - carry out the set up and axis checks and you should soon be making first class chips.

Pat