Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2001-09-28
2003-07-15
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S661000, C901S033000
Reexamination Certificate
active
06593756
ABSTRACT:
The invention relates to a device for registering contacts, comprising at least one force-sensitive transducer, whereby the force is coupled to the transducer via a fiber or a fiber bundle.
Tactile sensors are employed where ever interactions between a contact surface and the environment are to be measured and registered. In the simplest case, such tactile sensors serve the purpose of detecting contacts. In conjunction with the manipulations occurring in the field of robotics, such tactile sensors are expected to substitute for the sense of touch of humans and supply adequate information about the interaction occurring between the contact surface (the gripper or finger) and the sensed objects, so that movements and grips can be planned.
Different sensors are known with which tactile impressions can be technically registered (tactile sensors). The interaction with an object leads in this connection to a change in a quantity that is characteristic of the tactile sense. The change in such a quantity can be interpreted with the help of a suitable method.
It is possible to obtain static and/or dynamic tactile information depending on the engineering principle of such sensors.
Known sensors for accommodating tactile sensors are described in the following.
It is known that normal and shear forces can be measured via a capacitive cell, whereby normal forces are registered by changing the spacing between the electrodes as ell as the forces of shear by displacing the electrodes against one another (FAN, L. S., WHIT, R. M., and MULLER, R. S., 1984: “A Mutual Capacitive Normal- and Shear-Sensitive Tactile Sensor”. IEEE Int. Electron. Devices Mg; pages 220-222).
Normal forces can be measured also by means of piezo-resistive sensors. The firm Interlink-Electronics manufactures a foil that is imprinted with a semiconductive polymer, the resistance of which diminishes when pressure is acting on it. Such resistance can be measured with electrodes located underneath the foil (Interlink Electronics Europe 1990, G. D. de Luxembourg, “Pressure and Position Sensors: A Rising Technology”).
Vibrations can be measured with piezoelectric sensors by converting the occurring vibrations into an electrical voltage with the help of a piezoelectric material. Such electrical voltage can be interpreted by means of suitable methods. (JOCUSCH, 1996, “Taktile Sensorik für eine Roboterhand” [Tactile Sensorics for a Robot hand]; Technische Universität Bielefeld).
Dynamic information via approximated speed between the sensor and the object can be registered with inductive sensors. For example, it is possible to work two coils into an elastic material and to evaluate the changes occurring in the magnetic coupling in the presence of a change in the geometry. Furthermore, static measurements are possible in this manner as well (PEURA, R. A., 1978, “Basic Transducers and Principles”, in: J. G. Webster (ed.), Medical Instrumentation: Application and Design; Boston; Housten Mifflin).
A device of the type specified above is described in DE 42 40 531 C1. Said device is an input device for a computer and is designed in the form of a glove fitted with sensors. The known device serves for the registration of position and movement data of a hand and for transmitting such data to a computer. The known input device, furthermore, comprises contact sensors that serve for measuring the pressure distribution. As a sensor for determining the angle of deflection of the finger joints, the known device proposes as a transducer a coil that surrounds an immersion core that is movably supported in the coil. A flexible fiber is secured on the immersion core and transmits tensile and shear forces, so that the inductivity of the coil is changed by the movement of the immersion core when the finger joints are deflected. As tactile sensors, the known data glove is using pressure sensors designed in the form of flat capacitors whose plates can be moved against one another in an elastic manner when force is acting upon such plates. Different forces acting on the capacitor surfaces ensue different capacity values, which is exploited for determining the pressure acting on the plates.
The receptive elements of all sensors known heretofore are located either within the contact surface and come into direct contact with the sensed object, or the contact surface itself consists of a flexible layer and the receptive elements of the sensors are located directly underneath said layer. Such coupling between the receptive element and the sensed object suffices for static sensors whose function is to measure the forces.
However, dynamic sensors that are expected to register contact, speed and/or vibration are subjected to limitations on account of such coupling.
The mechanical properties of a contact surface are determined by the materials employed. Various goals can be pursued in this connection depending on the type of application. For example, in connection with contact with objects it may be desirable to build up a pressure as rapidly as possible or to achieve also as deep an impression as possible and to reduce the pressure in this connection only gradually, for example in order to permit the best possible adaptation to the object. Dynamic sensors are expected in this connection to take measurements, but not to determine the mechanical properties of the contact surface. However, this is in fact assured in connection with an arrangement in which conventional sensors are located beneath a flexible contact surface; however, the sensitivity and the accuracy of dynamic sensors are in this connection highly reduced, and are, furthermore, dependent upon the properties of the contact surface. With an arrangement that permits direct contact of the receptive elements with the contact surface, it is in fact possible to embed sensors within a flexible layer; however, such a flexible layer does not offer the stability required for providing it with any desired flexibility. The properties of the contact surface are in this connection decisively determined by the embedded sensors, and the distance from the contact to the build-up of a high pressure is in this connection generally only very short. Measurements are possible in each case only after the object has already touched the contact surface. To the extent to which no direct contact with the surface and contact surface takes place in the site of the sensor because of the geometric circumstances, no coupling of the sensor and the receptive element exists, and no measurements are possible.
Furthermore, the size and the type of coupling of the receptive elements of the known sensors does not allow obtaining any information about the surface structure of an object by scanning, unless such surface structure is quite rough.
The present invention is based on the following problems:
The goal is to register contacts dynamically, whereby the forces exerted on the sensed object are as low as possible. It should be nonetheless possible to exert on the object via a contact surface forces. However, such forces are to be independent of the interaction occurring between the object and the tactile sensor. It should be possible in this connection to collect tactile information before the object comes into contact with the contact surface. Furthermore, coupling between the sensor and the object is to be safely assured irrespectively of the geometric circumstances. Moreover, the tactile sensor should be suited for collecting information about the surface structure of an object.
For solving said problem, the invention proposes that the transducer converts the force acting on the fiber by means of a capacitor into electrical signals, whereby the fiber is mechanically coupled with one end to a first electrode of the capacitor, said electrode being displaceable in relation to a second electrode.
The special advantage offered by the device as defined by the invention consists in that the tactile impression is received via the free end of the fiber, whereby it is made possible owing to the mechanical coupling to the transducer to
Maël Eric
Schmidt Peer
Würtz Rolf
Benson Walter
Collard & Roe P.C.
Le N.
Rubitec Gesellschaft für Innovation und Technologie der Ruhruniv
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