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Hi all, Sami here from Avid CNC and this is a Pro-Tip video covering all you need to know about CNC Proximity Sensors.
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What do they do? How do they work? And why do I need them?
First of all, let's dive into what their function is on the Avid CNC machine.
The Pepperl + Fuchs NPN inductive proximity switches provide a complete solution
to automatically home your CNC machine, square your gantry, and to provide active safety limits
to prevent crashes and protect your machine and workpieces.
These sensors feature a repeatability of better than 0.001", over a large working temperature range.
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A proximity sensor is able to detect the presence of a nearby object without any physical contact.
The inductive proximity sensor emits an electromagnetic field and looks for changes in the field or return signal.
In this case it will detect the sensor flags, located at the end of each axis, when it enters the proximity sensors field.
The sensor sends signals to Mach4 that no, there is no object or yes, there is an object within its field.
This will allow the machine to move the motors on the gantry, X rack and pinion assembly, and the Z-axis spindle plate
a safe distance from the machine limits
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The proximity sensors are utilized in the homing sequence.
When you click the Home X, Y, & Z axes button,
the machine will travel along each axis until the sensor flags are within range of the proximity sensors.
This is a recommended part of the start up routine where the machine goes to the extents of each axis
and finds the limits or extreme positions of the table,
also known as the "Machine Home".
I like to think of this as the machine waking up in the morning,
it's a little sleepy and needs to search around for it's glasses on the bed side table
so it can figure out where it is in space.
It is recommended to home your machine each time you start Mach4,
power on your electronics, or anytime the axes have been dereferenced.
Such as when the E-stop has been activated.
The proximity sensors will also be essential in your initial machine build and setup
to ensure the gantry is square to the machine frame.
When the gantry moves forward to home it will use the two front sensors to align the two sides of the gantry.
To correct for squareness, adjust the depth of the sensor flags.
I've linked to the leveling, squaring, and tramming procedure below.
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Let's review the sensor locations.
WE have our Y1- switch,
Y2- switch,
Y2 + switch,
X switch,
and Z switch,
For our sensor flag locations, on the bumper plates there is the Y1 - sensor flag,
the Y2- sensor flag,
and Y2+ Sensor flag.
Best viewed from the back of the machine, we have the two X sensor flags
on the back of the gantry extrusion,
X+ and X-.
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Pepperl + Fuchs Proximity Sensor Kit is curated to easily install on all of our Standard, PRO, and Benchtop machine kits.
Let's cover a few of the varieties of proximity sensors that this kit includes.
The cube inductive proximity switch installs easily on any flat mounting surface.
These are installed on the Gantry Riser plates and reference the sensor flags on the table bumper plates.
The cube sensors will sere as the Y1-. Y2-, and Y2+ sensors.
These provide a 7mm detection distance against steel and 4.5 mm distance against aluminum.
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The cylindrical inductive proximity switch threads easily onto mounting plates and is held in place with a jam hex nut.
These provide a 8mm detection distance against steel
and 5mm detection distance against aluminum.
Locations for this sensor in our PRO machine kit includes the X axis and the Z axis.
The Z axis proximity sensor references the spindle mounting plate on the Z axis.
The extended range allows you to completely protect your limit switches with bumpers or other mechanisms and still have sensing range.
The X-axis proximity switch references two sensor flags on the back of the gantry for X- and X+.
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Our Benchtop CNC machines utilize the cylindrical proximity sensors on all axes.
There is the Y1-,
Y2-.
Y2+,
and the X axis has two proximity sensors.
The X- and X+
as well as the Z+ sensor.
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There are three kinds of limitations to our machine movements.
Physical limits,
sensor range,
and soft limits.
In this top down view we can see t he Y1-,
the Y2-,
and Y2+ sensors
as well as the Y1-, Y2-, and Y2+ sensor flags.
First let's focus on physical limitations,
this is how far the machine can physically move in each direction before the machine contacts the bumpers at each end of each axis.
Next, there is sensing range,
this is the area where when the machine moves to the extremes of each axis and the sensors can detect the sensor flags.
For example when the gantry moves toward the front of the machine in the Y- direction to home,
both Y1- and Y2- sensors will be in use and will detect the location of the two front sensor flags.
Then there are Soft limits, or software limits,
which is when the machine uses software to protect your CNC.
The machine will only allow movements a specified distance on each axis from the machine home,
which was established previously when the machine was homed and squared.
It is also good to understand the actual work area, this is the space the cutting tool, in this case the spindle, can access.
First we will home our CNC machine,
this brings the sensors within sensing range of the sensor flags.
After you home your Avid CNC machine, soft limits will turn on automatically in Mach4.
Now that the machine is homed and soft limits are enabled , if we move the machine in the Y- direction
the gantry slows down and stop at the end of the soft limits.
If we move the gantry toward the back of the machine to the Y+ soft limit,
the machine will stop at the set distance from our machine coordinates
set in our soft limits.
You can adjust your homing and soft limits in Mach4
and I've linked instructions on this in the description below.
Soft limits are also extremely helpful when running a program.
In Mach4 when you load a program that cuts outside of the soft limit area,
when you Cycle start the program, it will stop and provide and error message that the toolpaths are outside of this soft limit work area.
In the Mach4 toolpath preview window, you'll notice the yellow dash line.
This represents the boundary of the soft limits
which helps with the visualization of toolpaths that fall outside of this boundary.
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Let's walk through how to confirm the locations of your proximity sensors on your machine and in Mach4.
This technique can be used to troubleshoot sensor functionality and to confirm that the locations on the machine
match the part on the electronics enclosure the sensor cables were plugged into.
Ensure that you have installed and configured Mach4 and powered up your plug and play electronics.
In Mach4 we will navigate to the Diagnostics window on the bottom of our Mach4 interface.
Each sensor has an LED to quickly indicate function.
To check the functionality and location of each sensor, hold a wrench or something metallic to the sensor.
The sensor LED light should turn on and the corresponding signal in Mach4 will also light up.
This will confirm that the location of the sensors are correct when plugged into the controller.
Let's check that all of our sensors are connected correctly and functioning.
We have Y1-,
Y2-
Y2+,
X,
and Z+
That's all for this Pro-Tip video.