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. 2023 Nov 25;8(8):567.
doi: 10.3390/biomimetics8080567.

Low-Cost Angle Sensor for Robotics Applications Using Plastic Optical Fiber Based on Optical Loss Mechanism

Hyun-Woo Lee  1 , Dae-Hyun Kim  2 , Sangwoo Shin  3
Affiliations

Low-Cost Angle Sensor for Robotics Applications Using Plastic Optical Fiber Based on Optical Loss Mechanism

Hyun-Woo Lee et al. Biomimetics (Basel). .

Abstract

Robotic systems and the human body consist of numerous joint structures, all of which require precise angle adjustments. At present, encoder, strain gauge, and electrical resistance-based sensors are commonly used for angle measurement. However, these sensors have limitations when used in underwater or in environments with strong electromagnetic waves. Therefore, we have developed an angle sensor based on step-index profile plastic optical fiber (SI-POF), which is cost-effective and highly durable, in this study in order to overcome the limitations of existing angle measurement sensors. To this end, the amount of light loss according to the gab and angle changes that occur when the POF angle sensor is applied to the robot arm was experimentally measured, and based on the results, a simulation of the amount of light loss when the two losses occurred at the same time was conducted. In addition, the performance of the POF angle sensor was evaluated by measuring sensitivity and resolution, and comparative verification with a commonly used encoder was conducted to verify the reliability of sensors in extreme environments, such as those with electromagnetic fields and those that are underwater. Through this, the reliability and practicality of the POF angle sensor were confirmed. The results obtained in this study suggest that POF-based angle sensors can contribute to the development of the biomimetic robot industry as well as ordinary robots, especially in environments where existing sensors are difficult to apply, such as areas with underwater or electromagnetic interference (EMI).

Keywords: bending loss; coupling loss; electromagnetic interference (EMI); robot arm joint; step index profile plastic optical fiber (SI-POF); underwater.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Research flow chart.
Figure 2
Figure 2
Refractive loss due to reduced angle of incidence.
Figure 3
Figure 3
A beam of light continuing at the same angle of incidence within an arc.
Figure 4
Figure 4
Basic concepts of light intensity distribution modeling [22].
Figure 5
Figure 5
Illuminance distribution by plastic optical fiber area [22].
Figure 6
Figure 6
Experimental setup for a bending loss test.
Figure 7
Figure 7
Experimental setup for a coupling loss test.
Figure 8
Figure 8
Normalized light intensity according to radius.
Figure 9
Figure 9
Normalized sensitivity of light intensity according to radius.
Figure 10
Figure 10
Normalized light intensity according to gap between two aligned optical fibers.
Figure 11
Figure 11
Normalized sensitivity of light intensity according to gap between two aligned optical fibers.
Figure 12
Figure 12
Conceptual approach for rotating angle detection mechanism.
Figure 13
Figure 13
Normalized light intensity with initial gap of 0 mm, 4 mm, 8 mm and 12 mm (at r = 6 mm).
Figure 14
Figure 14
Normalized light intensity by radius change in rotating part (at di = 8 mm).
Figure 15
Figure 15
A robot arm part device with POF angle sensor.
Figure 16
Figure 16
Performance test result of POF angle sensor.
Figure 17
Figure 17
Normalized sensitivity of light intensity of POF angle sensor.
Figure 18
Figure 18
Exposing a magnetic field to each sensor: (a) POF angle sensor; (b) encoder.
Figure 19
Figure 19
Signal of POF angle sensor: (a) noise in a general environment; (b) interference in the magnetic field environment.
Figure 20
Figure 20
Signal of encoder: (a) noise in a general environment; (b) interference in the magnetic field environment.
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