Summary Analysis Draft #4

MEC 1281

Summary Analysis

Draft 4

By Sum Jin Yao

9 April 2021

According to the article "Soft robotic arm uses flexible sensors to understand its position" by Matheson (2020), MIT researchers have found a way to program a soft robotic arm to understand its structure in 3D space, using "motion and position data from its sensorized skin" (Rob.M, 2020).

 These soft robots are built from highly flexible materials, alike to "those found in living organisms" and are supported as "safer, and more adaptable, resilient and bioinspired alternatives to traditional rigid robots". Traditional sensors reduce a soft robot’s functionality and also complicate its manufacturing process.

 The researchers describe it as a system of soft sensors that wrap over the robot's body and that feedback to the internal AI to provide the robot "awareness of motion and position of its body". The article mentions their future goal is to advance artificial limbs, to be skillful to grip and operate objects in the environment, and also to incorporate body sensors in robotics.

 The soft robot's materials have "piezoresistive" properties. This means when its original shape undergoes any physical changes, its electrical resistance changes with it. The material shape is "inspired by kirigami”, with a variety of patterns etched on the rectangular silicone sheets. This changes the elastic of the material. However, I believe that the disadvantages of a piezoresistive sensor --- thermal dependence and external stresses --- outweigh its advantages.

 One of the disadvantages of the piezoresistive sensor is that the pressure sensor output varies under different temperatures. This is backed by the research article "Effects of Temperature and Residual San tresses on the Output Characteristics of a Piezoresistive Pressure Sensor", written by Anh Vang Tran. et al. (2019) stating that "temperature variations can change the values of the resistors". Additional supporting article (Liu, Y. et al., 2016) referring that higher temperatures will cause a drift in sensitivity output. Another problem that is resulted from high temperature is current leakage. Liu Yan, et al. (2016) said that when the temperature is above 150 degrees Celsius, there will be current leakage and reverse current flow. This will lead to an inaccurate sensitive output. The other problem with high temperatures is that metals such as aluminum, gold, or titanium will diffuse into the silicon membrane. Thus, silicone can only function as it is intended under a certain temperature, which greatly limits its use.

 Another disadvantage of the piezoresistive sensor is that external stress can occur during the processes of chip fabrication and packaging, which will affect the performance. This is supported by the research article "Thermal-Performance Instability in Piezoresistive Sensors: Inducement and Improvement", written by Liu Yan, et al. (2016) states that "There are mainly three sources of performance perturbation in the fabrication and packaging". The piezoresistive sensor is fabricated by placing resistors on top of the silicone membrane that is in high-stress regions (Anh Vang Tran. et al., 2019). The membrane requires fabrication before resistors can be placed on top of it. During this fabrication residual stress such as thermal, intrinsic, and quenching stresses are formed in the membrane. This would affect the output of the piezoresistive sensor.

 In conclusion, the disadvantages of the piezoresistive sensor, temperature dependence, and also external stresses that occur during processes of chip fabrication and packaging, outweigh its benefits. These disadvantages make the device not compatible in various extreme climate environments and also are more likely to make it prone to inaccurate sensor output.

 

References

Matheson, R. (2020, February 16). Soft Robotic Arm Uses Flexible Sensors to Understand Its Position. Control Engineering. www.controleng.com/articles/soft-robotic-arm-uses-flexible-sensors-to-understand-its-position/

Liu, Y., Wang, H., Zhao, W., Qin, H., & Fang, X. (2016, November 24). Thermal-Performance instability in piezoresistive sensors: Inducement and improvement. NCBI. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5190965/

Anh, V., Zhang, X., & Zhu, B. (2019, February 26) Effects of Temperature and Residual Stresses on the Output Characteristics of a Piezoresistive Pressure Sensor. IEEXplore. https://ieeexplore.ieee.org/abstract/document/8653271

Avent Abacus. (2019) Capacitive vs piezoresistive pressure sensors. https://www.avnet.com/wps/portal/abacus/solutions/technologies/sensors/pressure-sensors/core-technologies/capacitive-vs-piezoresistive-vs-piezoelectric/