Design

Simply put, a Pneumatic Deformation Sensor is a soft air bladder connected to an electrical pressure sensor. When the bladder deforms, whether it is being compressed, twisted or stretched, the air inside changes in pressure. This change in pressure can then be read by a pressure sensor and a microcontroller.

There are two designs available in this guide for PDS's. The first one is meant to demonstrate the concept and is meant to be squeezed and pulled. The second design is meant to show an application of PDS's and is a sensor attached to an existing soft robotic actuator.

Although any soft, airtight structure can be used as a PDS, certain geometries and specifications will function better than others. This is covered in-depth in the Sensor Design Guide.

The air bladder itself can be made from a variety of soft materials. Both of the designs shown use low-durometer silicones casted in 3D printed molds, however, there is nothing to prevent other soft and airtight materials from being used, such as airtight fabric or plastic.

The circuitry shown in this guide is based on the MPS20N0040D-D Pneumatic pressure sensor and needs an Op-Amp to amplify the signal and an Arduino microcontroller to read it. There are two circuits shown, one for a breadboard and one for a perfboard with soldered components.

Design 1

This design is meant to simply demonstrate Pneumatic Deformation Sensors and is designed to be an independent sensor. When the sensor is squeezed, its internal pressure increases to a maximum of 10 PSI. It consists of Ecoflex 00-30 silicone with an internal cavity of 21.5cm3 and a wall thickness of 6mm. The .STLs for the three-part mold are on the Downloads page and the Bill of Materials and the instructions for building can be found on the Fabrication page.

Design 2

This design is meant to show a use-case for Pneumatic Deformation Sensors. It consists of an Ecoflex 00-30 PDS attached to a PneuNets Bending Actuator. When the actuator is inflated, the sensor is bent, causing its internal pressure to increase up to 2 PSI. The sensor itself has an internal volume of 8.2cm3. The .STL for the mold are on the Downloads page and the Bill of Materials and the instructions for building can be found on the Fabrication page.

Sensor Design Guide

When designing a Pneumatic Deformation Sensor, it is useful to use Boyle's Law. Boyle's Law states that volume and pressure are inversely related. It's equation is P1V1 = P2V2, where P1 and V1 are the initial pressure and volume and P2 and V2 are final pressure and volume. In a PDS, P1 is ~15 PSI, as that is atmospheric temperature (the PDS code subtracts this). V1 is the volume of the internal chamber of the PDS when not deformed. In Design 1, this is 21.5cm3. In order to figure out the pressure that the sensor will output when deformed, the volume of the sensor when deformed is needed. This is difficult to quantitatively measure and will depend on the type of deformation that the sensor is sensing.For example, a sensor designed to sense bending will deform less than one that is designed to sense compression. When compressed by hand, Design 1's volume decreases to ~13cm3. If the values that are known are substituted into the equation, the value of P2 can be found to be ~25 PSI. With the atmospheric pressure (~15 PSI) subtracted, 10 PSI can be seen as the maximum pressure that the sensor will output. This can be reversely used to design a PDS that will give a desired pressure output. For example, a sensor with an output pressure of 5 PSI can consist of a volume of 15cm3 if it's minimum deformed volume is ~11cm3.

In order for a sensor to provide feedback for a soft robotic actuator, it must be designed so that the actuator deforms the sensor when actuated. In the case of Design 2, the PneuNets Bending Actuator bends, compressing the sensor beneath it.

Electronics

The electronics for a Pneumatic Deformation Sensor consists of the MPS20N0040D-D pressure sensor, the LM358 dual Op-Amp, and an Arduino microcontroller. There are two versions of the electronics, a version built on a breadboard with an Arduino Uno, and a version that is soldered to a perfboard with an Arduino Micro. The breadboard version is easier and quicker to build while the soldered version takes longer, requires more electronics skills, but is recommended for doing any serious work with PDS's. Both versions can be powered via USB. The diagrams and schematics for both systems along with the datasheets for the MPS20N0040D-D and the LM358 can be found on the Downloads page. The Bill of Materials and instructions for both versions can be found in the Fabrication section.

NOTE: The breadboard version of the electronics in this guide is shown with the Arduino and the breadboard attached via a case. This is not required.