MEC 1281
Summary Analysis
Draft #3
By Sum Jin Yao
22th Feb 2021
According to an article by M,Rob. (2020), MIT researchers
have found a way to program soft robotic arm to understand its structure in 3D
space, using "motion and position data from its own "sensorized
skin".
These soft robots are built from highly flexible materials,
alike to "those found in living organisms", are supported as
"safer, and more adaptable, resilient and bioinspired alternatives to
traditional rigid robots". Traditional sensors reduce a soft robot
functionality and also complicate its manufacturing process.
The researchers narrate it as a system of soft sensors that
wrap over the robot's body, that feedback to the internal AI to provide the
robot "awareness of motion and position of its body". The article
mention, their future goal is to advance artificial limbs, to be skilful 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 mean when its original shape undergoes any physical changes,
its electrical resistance changes with it. The material shape is "inspired
by kirigami”, with a variation of patterns etched on the rectangular silicone
sheets, this changes the elastic of the material. However, I believe that the
disadvantages of piezoresistive sensor such as thermal dependence and external
stresses outweighs its advantages. Other sensors such as piezoelectric is far
better and could be used instead.
One of the disadvantages of piezoresistive sensor, is that
the pressure sensitivity output varies under different temperature. This is
backed by the article (Anh,V. et al. , 2019) stating that "temperature
variations can change the values of the resistors", also with additional
article (Liu,Y. et al., 2016) stating that at higher temperature will cause a
drift in sensitivity output. Another problem that is resulted from high
temperature is current leakage. The article by (Liu,Y. et al, 2016) said that
when temperature is above 150 degree Celsius, there will be current leakage and
reverse current flow. This will lead to inaccurate sensitive output cause by
the high temperature. The other problem with high temperature is that metals
such as aluminium, gold or titanium will diffuse into the silicon membrane. Thus,
it can only function as it is intended under certain temperature, which greatly
limit its uses.
Other disadvantages of piezoresistive sensor, is that the
external stress can occur during the processes of chip fabrication and
packaging, it will affect the performance.
This is supported by the article (Liu,Y. et al. , 2016) stating that
"There are mainly three sources of performance perturbation in the
fabrication and packaging". Piezoresistive sensor is fabricated by placing
resistors on top of the silicone membrane that are in high-stress regions (Anh,V.
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 piezoresistive sensors such
as temperature dependence and also external stresses that occur during processes
of chip fabrication and packaging, outweighs its benefits. These, disadvantages
make the device not compatible in varies extreme climate environments and also are
more likely to be prone to inaccurate sensitivity output.
Liu.Y, Wang,H.
(2016, Nov 24) Thermal-performance instability in piezoresistive sensors:
Inducement and improvement.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5190965/
Avnet (n.d)
Capacitive vs piezoresistive vs piezoelectric pressure sensors.
Anh,V. (2019) Effects
of Temperature and Residual Stresses on the Output Characteristics of a
Piezoresistive Pressure Sensor.
https://ieeexplore.ieee.org/abstract/document/8653271
