OverviewThanks for purchasing our inductive Proximity Limit Switch Kit. This guide goes through the physical setup of the switches, wiring, and setup in Mach 3. These sensors will be used to accomplish multiple functions, both as limits (if you desire) and as homing switches that allow your machine to return to a known location and coordinate system after a power down or other event that causes it to lose position.
While these switches can work with Nema 23 setups using the G540, this requires use of a terminal block and 12V power supply to power the switches, which we'll cover in a separate article.
Physical Installation
The switches are intended to mount to the bumpers of your machine using the provided brackets. Position the sensors such that the face is roughly even with the edge of the rubber bumper. The sensors have approximately a 4mm sensing distance, so if they are recessed slightly from the bumpers, this will still work and will protect the sensors in the event of a crash.
When installing the sensors, the physical connection of the kit should be set up such that you have 3 sensors mounted to the machine base (CRP110 assembly), and 2 sensors attached to the gantry. See the following diagram:
If your directions are defined differently, homing will still work. However, there are two key factors to insure an easy installation:
- The home switches for the X axis and the X prime axis must be on the same end of the machine, as the machine will be moving both X and X prime in tandem until the switches are tripped.
- Both home switches should be at the minus end of the X axis travel, as the machine will define this limit as X = 0 when the sensor is tripped.
Wiring
Once the switches are physically in place, the next task is to connect the cables to the sensors and to your electronics. The example below shows how to accomplish this with our pre-wired kits, which use our panel mountable Input Breakout Board. However, the same wiring can be made directly to the PMDX-126 card if you have a DIY kit.
The sensors included can run off of unregulated DC power, and are rated for 6-36 VDC. The PMDX-126 supplies unregulated 12V power for use with sensors on terminals J11 and J12. If you are using a pre-wired kit, this power is wired to the Input Breakout Board, and should be selected by moving the red jumper on the back of the board to the “12U” position, as shown below (this will require unplugging and opening your enclosure):
At this point, it’s time to wire the switches into your system. You will be using 3 total inputs for 5 sensors. The X+ and X- sensors will share an input, as will the Y+ and Y-. The slave X sensor will have its own input – this allows the machine to auto-square. While the shared signals can be broken out into separate signals, it typically is not important to know whether you have hit a positive or negative limit, just that you have hit a limit. The shared signal arrangement makes the best use of the limited inputs on a single parallel port, as only 5 total inputs are available, and one of these is used for the emergency stop switch.
If you purchased a pre-wired kit with an Input Breakout Board, you will use the supplied 3 pin connectors to wire up the sensors. The sensors follow standard NPN input wiring color conventions:
- Black = Signal
- Brown = V+
- Blue = GND
These wires can be inserted into the 3 position terminals supplied with your kit using a simple screwdriver to actuate the spring loaded mechanism inside the terminal. A vise or clamp can be helpful for this.
On the inputs that are shared, the wire ends of two sensors can be wound together and then inserted.
These sensors can now be plugged into the Input Breakout Board on the bottom of your control panel.
If the LEDs are glowing on the sensors, and if these LED’s change when a piece of metal is placed in front of the sensor, you have them wired correctly.
Mach Setup
At this point, you should be ready to set up Mach 3 for your new sensors, so that Mach knows what inputs are used for what purpose. A bit of background may be helpful for those unfamiliar with Mach. A normally configured parallel port offers 5 general purpose inputs that can be assigned in Mach to different purposes – touch probes, limit switches, homing switches, etc. These inputs are on pins 10, 11, 12, 13, and 15 of the 25 pin parallel port. In our pre-wired kits, pin 10 is used to communicate to Mach when an e-stop has been pressed, so only 4 inputs remain. In the screen shots below, you will see certain pins assigned to certain functions. You may need to swap these numbers depending on where you plug in your sensors, but you will always be choosing between numbers 11, 12, 13, and 15.
The first step is to assign each of the limits and home switches to pins. This can be done through the Config->Ports and Pins menu, using the Input Signals tab. To start, set your signals up as seen in the screen below (broken into two pictures, as you will need to scroll down to the slaved “A axis”:
Note that the home, negative limit, and positive limit for X all share the same pin number, and the same is true of the Y – this is because the home and negative limit are using the same physical switch, and because we have the other positive limit switch tied into the same input. If we re-assign the pin number, we need to re-assign all 3 of these.
Also note, these sensors need to be configured as “active low”, and they all need to be “enabled”.
Once you have made the pin assignments, the next step is to check our work. The best way to do this is through the Mach diagnostics screen. You can get there by hitting Alt-F7, or using the tab across the top of the Mach interface. Once here you can put a piece of metal in front of your sensors. The yellow lights on “M1++ Limit, M1—Limit, and M1Home” should light up whenever either of the Y sensors (plus or minus) is tripped. Note this will also create an estop condition, so you will need to hit the reset button if you need to move the machine:
The yellow lights on “M2++ Limit, M2—Limit, and M2Home” should light up whenever either of the X sensors (plus or minus) is tripped:
Lastly, the yellow light on “M4Home” should light up whenever the X prime sensor is tripped:
If you are not getting these results, you will need to re-assign the pins to different pin numbers until you do. Some models of the pre-wired kits were wired to different default inputs, so this may be the case. Fortunately, the changes are easy to make – just remember that for X and Y, you need to re-assign all 3 functions (positive and negative limits as well as the home).
If you get the correct yellow lights as described above, you are ready to assign the homing functions. This is done through the Config->Homing/Limits tab. Set up your homing and limit switches per the screen below:
Note that the z axis is not enabled. Z limits can be configured, but the z axis needs to be reset whenever a tool is changed, so this option is not part of our kit, as this input is reserved for an auto-tool setter (coming soon).
After this, save your settings under Config->Save Settings. You are ready to home!
At this point, you can return to the main running screen in Mach. Make sure your z axis is up and out of the way, as this will not be part of the homing sequence. Now, when you press the “Ref all Home button”, the machine will home the Y axis first, and then the X and X prime simultaneously. When each side trips the sensor on its respective side, it will stop and back off the sensor. Check the squareness of your machine after homing, and make any necessary adjustments by threading the sensors in and out of their brackets, then re-homing.
Gotchas:
There are just a few things to check before homing the machine for the first time:
- First, make sure you have the X prime sensor on the same side as the “A” drive motor (slaved axis). Otherwise, you can get some strange behavior, with the X axis stopping when the X prime sensor is tripped.
- Make sure the acceleration and velocity are set the same for both X and slaved A axis. While normally this doesn’t matter (during operation, the A axis completely mimics the X) during homing these axes are temporarily decoupled, and Mach uses the independent settings programmed in for each.
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