Pressure mapping system with capacitive measuring pad
First Claim
1. A system for monitoring the distribution of forces on a surface, comprising:
- a pad having first and second arrays of linear electrodes respectively disposed on opposite sides of a sheet of compressible insulating material, the electrodes of said first array being oriented in a direction other than the direction of orientation of the electrodes of said second array to thereby form a matrix of nodes each of which is located at an intersection of an electrode of one array with an electrode of the other array and which has a capacitance that varies in accordance with compression of the insulating material at said intersection;
means for sequentially selecting the electrodes of said first array and applying an electrical driving signal to the selected electrode;
means for sequentially selecting the electrodes of said second array;
means for sensing an electrical current of the selected electrode of said second array to thereby measure the capacitance of the associated node at the intersection of the two selected electrodes;
means for connecting each of the non-selected electrodes of said first array to a reference voltage to thereby isolate said sensed node from the effects of changes in capacitance of nodes other than said sensed node whose capacitance is being measured; and
means for connecting each of the electrodes of said second array, including the selected electrode of said second array, to said reference voltage to thereby further isolate said sensed node from effects of changes in capacitance of nodes other than said sensed node whose capacitance is being measured and to reduce the effects of cable capacitance on the current from said sensed node.
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Accused Products
Abstract
A capacitive measuring pad is constructed of transverse conductive strips separated by a compressible insulator to form a matrix of pressure sensitive capacitive nodes. The nodes are repetitively scanned in sequence by a microcomputer to measure their respective capacitances, from which measurements a pressure map is then derived. The resulting pressure map may be displayed on a color graphics monitor with different colors representing diffrent pressures. Node capacitance is found by measuring the response of the mode to a driving signal of a known voltage. This measurement is accomplished by connecting one of the node'"'"'s transverse conductive strips to the driving source and the node'"'"'s other conductive strips to a sense amplifier. In order to isolate the node of interest from the influence of surrounding nodes, all of the conductive strips except the two intersecting the selected node are connected to ground. Furthermore, the input impedance to ground of the sense amplifier is made negligibly small with respect to the other system impedance. In this way, only the conductive strip connected to the driving source has a voltage impressed on it, and the conductive strips of all other nodes in the system are maintained at ground potential, thus allowing an accurate measurement of the one capacitance.
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Citations
21 Claims
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1. A system for monitoring the distribution of forces on a surface, comprising:
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a pad having first and second arrays of linear electrodes respectively disposed on opposite sides of a sheet of compressible insulating material, the electrodes of said first array being oriented in a direction other than the direction of orientation of the electrodes of said second array to thereby form a matrix of nodes each of which is located at an intersection of an electrode of one array with an electrode of the other array and which has a capacitance that varies in accordance with compression of the insulating material at said intersection; means for sequentially selecting the electrodes of said first array and applying an electrical driving signal to the selected electrode; means for sequentially selecting the electrodes of said second array; means for sensing an electrical current of the selected electrode of said second array to thereby measure the capacitance of the associated node at the intersection of the two selected electrodes; means for connecting each of the non-selected electrodes of said first array to a reference voltage to thereby isolate said sensed node from the effects of changes in capacitance of nodes other than said sensed node whose capacitance is being measured; and means for connecting each of the electrodes of said second array, including the selected electrode of said second array, to said reference voltage to thereby further isolate said sensed node from effects of changes in capacitance of nodes other than said sensed node whose capacitance is being measured and to reduce the effects of cable capacitance on the current from said sensed node. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. Apparatus for sensing the distribution of pressure on a surface, comprising:
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first and second sheets of compressible insulating material; a first array of linear electrodes interposed between said sheets of material and being oriented in a first direction; a second array of linear electrodes disposed on a side of said first sheet that is opposite said first array and being oriented in a second direction which intersects said first direction; a third array of linear electrodes disposed on a side of said second sheet that is opposite said first array, the electrodes of said third array being parallel to and in substantial alignment with the electrodes of said second array, each electrode in said third array being electrically connected to a corresponding aligned electrode in said second array to thereby effectively form two capacitors connected in parallel at each node formed at the intersection of an electrode in said first array with an aligned pair of electrodes in said second and third arrays; and means for sensing an electrical current of a selected electrode of said first array to thereby measure capacitance of an associated node, said electrodes of said first array, including said selected electrode being connected to a common reference voltage. - View Dependent Claims (15, 16, 17)
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18. A system for monitoring the distribution of forces on a surface, comprising:
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a pad having first and second arrays of electrodes and insulating material disposed between said first and second arrays to form a matrix of capacitive nodes each of which has a capacitance that varies in accordance with the degree of pressure on the pad at the location of the node; means for scanning the electrodes of said first and second arrays to thereby successively address nodes in said matrix; means for measuring the capacitance of an addressed node by sensing current of a scanned electrode of said second array; and means for connecting each electrode of said second array to a reference potential for the driving signal to thereby render all electrodes of said second array at substantially zero volts to thereby isolate the measured capacitance from the effects of changes in capacitance of nodes other than the addressed node whose capacitance is being measured. - View Dependent Claims (19, 20, 21)
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Specification