Sensor for Three Components of Grasping Force and Position Using Quartz Resonators

Abstract

Many force sensors used in robots use strain gauges. Because they have an analogue output, these force sensors are readily affected by electrical noise. They also often require amplifiers because of the low signal level, low pass filters to decrease electrical noise and A-D converters to interface with computers. On the other hand, force sensors which use quartz resonators are robust to electrical noise since the output is a frequency shift in response to a change in an external force. The frequency output of the force sensor can be easily converted into a digital signal through a frequency counter. This type of force sensor also has quick response, high sensitivity, high resolution and wide bandwidth. Therefore, it could be used in an environment with a high electrical noise background and where a quick response is needed. Although force sensors with quartz resonators have many advantages, as mentioned above, such sensors have not yet been applied in measuring dynamic force such as in a grasping force sensor. In this paper, first, mechanical strength of quartz resonators mounted in a robot finger was examined experimentally to static and impulsive forces. Secondly, the relationship between the external force and frequency shift of quartz resonators is discussed. Thirdly, a differential method applied to a robot sensor using quartz resonators is proposed. Finally, the response of the force sensor to an oscillatory force is discussed. On the basis of the aforementioned, a sensor for three components of grasping force and position using three pairs of quartz resonators is proposed. The force sensitivity of the sensor is independent of the grasping position on the finger. Performances of such a force sensor was examined experimentally.