A tactile sensor is a sensor used in a robot to mimic a tactile function.
Tactile sensation is an important sensory function when people are in direct contact with the external environment.
Developing a tactile sensor that meets the requirements is one of the key technologies in the development of robots.
With the development of microelectronics technology and the emergence of various organic materials, a variety of tactile sensor development solutions have been proposed.
However, most of them are currently in the laboratory stage, and there are not many products that have reached productization.
The tactile sensor can be roughly classified into contact sensor, force-torque sensor, pressure sensor, and sliding sensor according to functions.
The touch sensor is used to determine whether the robot (mainly the limbs) is in contact with an external object or a sensor that measures the characteristics of the object being touched.
The contact sensor has a type of micro switch, conductive rubber, carbon sponge, carbon fiber, pneumatic reset device, etc.
① Micro switch
It consists of spring and contact.
When the contact contacts the external object and leaves the substrate, the signal path is broken, thereby detecting contact with an external object.
The advantage of this normally closed (always on when not in contact) microswitch is that it is easy to use and simple in construction.
The disadvantage is that it is prone to mechanical oscillations and the contacts are susceptible to oxidation.
② Conductive rubber type
It uses conductive rubber as a sensitive component.
When the contact is pressed against an external object, the conductive rubber is pressed to change its resistance, so that the current flowing through the conductive rubber changes.
The disadvantage of this type of sensor is that the drift and hysteresis characteristics of the conductive rubber are also inconsistent due to differences in the material formulation of the conductive rubber.
The advantage is flexibility.
③ Carbon sponge type
It is provided with an elastomer composed of sponge on the substrate, and carbonaceous sponge is arranged in an array in the sponge.
After the contact object is pressed, the resistance of the carbon-containing sponge is reduced, and the magnitude of the current flowing through the carbon-containing sponge is measured to determine the degree of compression.
This sensor can also be used as a pressure sensor.
The utility model has the advantages of simple structure, good elasticity and convenient use.
The disadvantage is that the uniformity of carbon distribution directly affects the measurement results and the recovery ability after compression.
④ Carbon fiber type
The carbon fiber is used as the upper surface layer, the lower surface layer is the substrate, and the middle is filled with urethane and metal electrode.
When contacting an external object, the carbon fiber is pressed and electrically connected to the electrode.
The advantage is that it is flexible and can be mounted on the curved surface of the robot arm, but the hysteresis is serious.
⑤ Pneumatic reset type
It has a flexible insulating surface that deforms when pressed, and compressed air acts as a resetting force when disengaged.
When it comes into contact with an external object, its internal elastic bubble (yttrium copper foil) is in contact with the lower contact and conducts electricity.
The advantage is that it is flexible and reliable, but requires a compressed air source.
The slip sensor is used to determine and measure the slip caused by the object when the robot grips or transports the object.
It is actually a displacement sensor.
According to the presence or absence of the sliding direction detection function, it can be divided into three categories: non-directional, unidirectional and omnidirectional.
① Non-directional sensor has a probe earphone type, which consists of sapphire probe, metal bumper, piezoelectric Rochelle salt crystal, and rubber bumper.
The probe vibrates as it slides and is converted to the corresponding electrical signal by the Rochelle salt.
The role of the buffer is to reduce noise.
② The unidirectional sensor has roller photoelectric type.
The slip of the object being grasped causes the drum to rotate, causing the photodiode to receive an optical signal transmitted through the code wheel (mounted on the circular surface of the drum), and the sliding of the object is detected by the corner signal of the drum.
③ The omnidirectional sensor uses a metal ball whose surface is covered with an insulating material and constitutes a conductive and non-conductive region distributed by the warp and weft.
When the sensor contacts the object and produces sliding, the ball rotates, so that the conductive and non-conducting regions on the spherical surface alternately contact the electrode, thereby generating an on-off signal, and the magnitude and direction of the slip can be measured by counting and judging the on-off signal. .
This sensor requires a high manufacturing process.