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Robotic Gripper Slip Sensor Using Ultrasound

IP.com Disclosure Number: IPCOM000062386D
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Brennemann, AE: AUTHOR

Abstract

Using ultrasound, with amplitude modulation, phase modulation, or Doppler frequency shift, permits a robot gripper to use all electronic sensing to detect motion dynamics of a loosely gripped object during slippage. Using amplitude modulation of an ultrasonic carrier allows detection of slippage. Using phase modulation or Doppler shift allows detection of slippage and also allows determination of the direction of slippage. Amplitude Modulation System An amplitude modulation system is illustrated in Fig. 1. An emitting transducer 1 is attached to gripper face 2, and a receiving transducer 3 is attached to gripper face 4. A continuous sine wave of ultrasonic energy, excited by transducer 1, is propagated throughout face 2.

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Robotic Gripper Slip Sensor Using Ultrasound

Using ultrasound, with amplitude modulation, phase modulation, or Doppler frequency shift, permits a robot gripper to use all electronic sensing to detect motion dynamics of a loosely gripped object during slippage. Using amplitude modulation of an ultrasonic carrier allows detection of slippage. Using phase modulation or Doppler shift allows detection of slippage and also allows determination of the direction of slippage. Amplitude Modulation System An amplitude modulation system is illustrated in Fig. 1. An emitting transducer 1 is attached to gripper face 2, and a receiving transducer 3 is attached to gripper face 4. A continuous sine wave of ultrasonic energy, excited by transducer 1, is propagated throughout face 2. If an object 5 is placed between faces 2 and 4, sound waves will be transmitted through the gripper face 2 and through object 5 to gripper face 4. If the amplitude of the carrier envelope is constant, then no modulation of the carrier will be detected. If object 5 slips or is moved, then an interruption of the carrier will occur and appear as a modulation of the carrier. This occurs because of an instantaneous interruption of the coupling of the emitting transducers to the receivers. This can easily be detected as modulation or even as noise. As an example, if transducer 1 emits a 230 KHz sound wave carrier, then receiving transducer 3 can be tuned with proper filters to reject unwanted low frequencies, such as microphonics or random noises. Other signal-enhancing techniques can be used to allow detection of the modulation of the carrier caused by the slipping object. Advantages of this system are: 1)A traditional amplitude modulation receiving system can be used for detection.
2)Low frequencies can be used for the carrier. 3)The carrier system can be filtered to reject spurious responses such as microphonics or random vibration. A disadvantage is that direction or velocity of the slipping object is not detected. Multi-Receiver System for Phase Modulation Detection Another system using phase shift or Doppler shift for slip detection is shown in Fig. 2. An ultrasonic transducer 6 is affixed to gripper face 7 in such manner that transducer 6 is electrically excited with sine waves. Sound waves are generated throughout face
7. When the contact area between object 9 and face 8 is smaller than the surface area of face 8, (the contact area could even be a number of points within face 8), sound energy is conducted from face 7 through object 9 into, and distributed throughout, face 8. The area of contact then acts as a localized transmitter of ultrasound to face 8. The materials of faces 7 and 8 and object 9 are such that the velocity of sound through them are considerably greater than the velocity of sound in air. Sonic receiving transducers 10 and 11 are placed on opposite edges of face 8, so that sound energy coupled into face 8 will arrive at each receiver with a delay prop...