Tham khảo tài liệu 'crc press - robotics and automation handbook episode 1 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | I B FIGURE Hall effect sensor. Ultrasonic Sensors Ultrasonic displacement sensors use the same approach as optical time-of-flight sensors with an analog output proportional to the distance to target. Instead of a light pulse however an ultrasonic pulse is generated reflected from a target and then detected by a receiver. The response is dependent upon the density of the target. The frequency of the ultrasonic pulse is greater than 20 kHz and thus beyond the audible range for humans. Piezoelectric and electrostatic transducers are typically used to generate the ultrasonic pulse. As compared with optical time-of-flight sensors ultrasonic sensors are less sensitive to light disturbances. However ultrasonic sensor output can be affected by large temperature gradients because the speed of sound is affected by air temperature. Hall Effect Sensors Hall effect sensors are noncontact sensors which output a signal proportional to input magnetic field strength. The Hall effect refers to the voltage generatedwhen a current carrying conductor or semiconductor is exposed to magnetic flux in a direction perpendicular to the direction of the current. A voltage the Hall voltage is generated in a direction perpendicular to both the current I and the applied magnetic field B as shown in Figure . In order to use a Hall effect sensor as a displacement sensor the sensor is typically matched with a moving permanent magnet. This magnet is applied to the target. Since the output of the Hall effect sensor is directly proportional to the applied magnetic field strength the output will be nonlinearly related to the distance from the sensor to the permanent magnet. This nonlinear relationship must be included in the post processing of the output signal. The sensor is most often made of a semiconductor material and therefore is available in standard integrated circuit packages with integrated electronics. Strain The most common strain sensor used in robotics is
