FSR Leveling

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This is my first blog post of many of findings whilst I researched into the design of my 3d Delta printer. This post will cover FSR’s used in the case of Spatial One (my 3D delta printer) for bed levelling. I have tried many methods of bed leveling and using FSR’s to this date is very reliable and accurate although in the future i will look at more cost effective and accurate solutions.

 

Basics on bed leveling:

A FSR bed leveling system works by having three FSR’s on the circumference of the bed, when the probe (usually the hot end) makes contact with bed the FSR’s change in resistance and the electronics controlling the printer detects this.

FSR definition:
Force Sensing Resistor optimized for use in human touch control of electronic devices such as automotive electronics, medical systems, and in industrial and robotics applications. FSRs are two-wire devices. They are robust polymer thick film (PTF) sensors that exhibit a decrease in resistance with increase in force applied to the surface of the sensor.

 

The set up of the bed leveling for the smoothie board on Spatial One:

I use 3 FSR’s (force sensitive resistors) under the bed and FSR controller by John Socha-Leialoha’s. The FSR are placed under the circumference of the bed at 3 equidistant points and connected to the FSR controller and the controller connects to the z max on the smoothie board. Then i run the G32 command and the smoothie board runs the full calibration sequence automatically, where the hotend acts as the z probe and the FSR detects the probe contacting the bed.

 

FSR controller available from our website

FSR Controller
FSR Controller

 

I looked at two types of FSR’s; FSR 400 and FSR 402 from our website FSR 402 .

The FSR 400 has the following specification:

Active Area: Ø5.08mm
Nominal Thickness: 0.30mm
Switch Travel: 0.05mm
The FSR 402 has the following specification:
Active Area: Ø14.68mm
Nominal Thickness: 0.46mm
Switch Travel: 0.15mm
I favoured the FSR 400 as it has a shorter switch travel which i thought would make the level sensing more sensitive and accurate. I designed two different pads to hold each of the FSR types one below shows the FSR402.
FSR400
FSR400

 

FSR402
FSR402
 The problem i had with the FSR400 with having such a small active area of Ø5.08mm it did not stick to the plate very well and kept coming off, where as the FSR402 had a bigger active area and therefore a bigger area to stick to the plate. After testing different ideas of holding the FSR400 i decided to keep the FSR402.

 

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