MINIATURISED DEVICE FOR SENSING THE SURFACE FORCE DISTRIBUTION

Abstract: A miniaturised force sensor device for sensing a surface force distribution includes a metal plate to which a printed board is applied for supporting a plurality of sensors made of a ceramic support on which a resistive paste is printed, such resistive paste having contacts that can be connected by soldering to the contacts of a printed board to make a mechanical, electrical connection.

Description: Miniaturised device for sensing the surface force distribution The present invention relates to a miniaturised force sensor device for sensing a surface force distribution. In many field, as it is known, there is the need to sense the distribution of forces acting perpendicularly to a surface. In particular, it is necessary to carry out measurements of the forces exerted by tires on the ground in order to investigate the tire bearing pressure when the static load changes and the behaviour of the sliding pressure when the tire rotates at different speeds. An exact measurement of the forces under the tires is important to optimise the efficiency and the wear resistance of the latter through the investigation of a variety of tire shapes and treadings . Also in orthopaedia it is necessary to measure the distribution of the forces generated by the human body on the ground, particularly at the bearing of feet. In fact it is very important to investigate the distribution of the body weight on the foot sole as well as it is necessary to investigate the pressures generated on the ground during walking. Actually the static, dynamic investigations of the foot bearing are essential for sensing bearing irregularities as well as prescribing and designing corrective shoes and shoe soles . Also during the recovery it is necessary to calculate and display the projection of the centre of gravity to the bearing area on a monitor in real time in order to let people to practise and to recover people that have undergone traumas influencing their stability as well as the capability of controlling their own body. In order to carry out such measurements, there are presently provided footboards or surfaces using piezoresistive or capacitive sensors which are absolutely not capable of providing a high space resolution associated to a reading precision so that it is not possible to draw exactly a correct map of force or pressure distribution. The present invention seeks to solve the problem set forth above by providing a force sensing device which allows the distribution of forces in miniaturised spaces to be determined, thus also allowing a local distribution of forces in extremely small spaces to be sensed with very high precision in real time. With regard to the object set forth above, a particular object of the invention is to provide a sensor device which is capable of withstand also a considerable stress without undergoing structural modifications that could change its operating precision. A further object of the present invention is to provide a device which is capable of ensuring the highest reliability and safety of use owing to its peculiar features. Not last aim of the present invention is to provide a miniaturised force sensor device for sensing the surface force distribution which can be easily manufactured by using elements and materials that can be readily found on the market, such device being further competitive from an economic point of view. The aim mentioned above as well as the cited objects and others that will be better pointed out thereafter are accomplished by a miniaturised force sensor device for sensing the surface force distribution, characterized in that there is provided a metal plate to which a printed board is applied for supporting a plurality of sensors made of a ceramic support on which a resistive paste is printed, such resistive paste having contacts that can be connected by soldering to the contacts of a printed board to make a mechanical, electrical connection. Further features and advantages of the objects of the present invention will be more readily apparent from the following description of a preferred but not exclusive embodiment of a miniaturised force sensor device for sensing the surface force distribution shown by way of an illustrative, but not limitative, example by means of the accompanying drawings, in which: Fig. 1 shows schematically a perspective view of the force sensor device according to the invention; Fig. 2 shows the electric operating circuit. With particular reference to the numerals of the above-mentioned Figures, the miniaturised force sensor device for sensing the surface force distribution according to the invention includes a thick metal plate 1 to which a printed board 2 is glued by a structural glue so that the circuit itself does not undergo deformation . Sensors 3 made by thick or thin film technology are applied to the printed board by printing a resistive paste 4 on a ceramic layer 5. Resistive paste 4 forms contacts 6 which are connected by soldering to the corresponding contacts 8 of the printed board. Soldering have the function of providing a mechanical fastening to the printed board and at the same time an electrical connection to the other sensors and the outside interface and control circuits. The single sensor on the ceramic may have a variety of resistances. In addition, support means 10 are provided in the printed board so that the deformation of the ceramic is facilitated. In fact upon application of a force to the sensor, the ceramic deforms and causes the resistance to extend and to change its value. The variation of the resistance is linearly proportional to the force applied to the single sensor. The sensors formed by one resistance are arranged on a matrix of columns and rows and are connected to the printed board. The signals sensed by the sensors are fed to the outside through connectors provided on the printed board . The operating electronics, as shown in Figure 2, includes essentially a microcontroller 20 which provides for controlling data collection and is connected via an analogue-to-digital converter 21 to a first multiplexer 22 which is connected to operational amplifiers 23 which are associated to the rows of the sensor matrix and detect a voltage that varies depending on the sensor resistance. A second multiplexer 25 operating one sensor column at a time is provided. Microcontroller 20 is associated to a data storage memory 27, moreover an interface 28 for the connection to a PC 29 is provided. The electronics provided with a microcontroller collects and stores force values from the matrix as well as operates according to a series communication protocol or is computer-aided. The computer software displays the maps of forces on the plane of the matrix and the interface circuit provides to the insulation among cells so that any sensor senses only the force applied to its surface. The reference voltage used by the operational amplifiers may vary from 100 mV to 10 V depending on the next amplification circuit and the power supply. Microcontroller operates one column at a time by controlling the second multiplexer. The voltage of the operated column will then be present at the output of the amplifiers. The microcontroller converts the signal of one amplifier at a time and the converted data is then stored in a local memory. The communication protocol to the computer controls the transmission of such data to the computer so that it can be processed and displayed as well as stored in the bulk memory of the computer. The electronics of the computer provides for the compensation of the initial errors in each sensor and corrects the differences in the dynamic response of the single sensors . The thus connected and arranged sensors have the objects of providing a map of distribution of the forces perpendicular to the surfaces so that they are particularly suitable for the application to different fields such as the forces under the tires and the forces acting on a walking surface in orthopaedia. From the foregoing one can see how the invention accomplishes the proposed objects. Moreover, it should be appreciated that a particularly practical and functional sensor device is provided. The thus conceived invention may undergo a number of modifications and changes, all of them within the scope of the inventive step. Furthermore, all of the construction details may be replaced by other equivalent components. In practise, the employed materials as well as the size and the shapes may be varied according to the requirements .

Claims: Claims 1. A miniaturised force sensor device for sensing a surface force distribution, characterized in that there is provided a metal plate to which a printed board is applied for supporting a plurality of sensors made of a ceramic support on which a resistive paste is printed, such resistive paste having contacts that can be connected by soldering to the contacts of a printed board to make a mechanical, electrical connection. 2. The miniaturised force sensor device according to claim 1, characterized in that there are provided bearing points among sensors and the printed board in order to reduce the shear stress at the soldering point as well as the mechanical hysteresis. 3. The miniaturised force sensor device according to the preceding claims, characterized in that said sensors are arranged according to a matrix. 4. The miniaturised force sensor device according to one or more of the preceding claims, characterized in that there is provided a data processing means formed of a microcontroller operatively associated to a first multiplexer to receive signals from the single rows of sensors, the microcontroller being also connected to a memory through an analogue-to-digital converter, a second multiplexer being also provided for scanning the columns of sensors . 5. The miniaturised force sensor device according to one or more of the preceding claims, characterized in that there are provided operational amplifiers, the output voltage of which depends on the resistance of the sensor. 6. The miniaturised force sensor device according to one or more of the preceding claims, characterized in that said microcontroller is connected to a computer for controlling data and displaying the force distribution in real time.

Inventors: JABIR SAAD, JABIR, SAAD
Applicants: ENCASS S R L, JABIR SAAD, ENCASS S.R.L., JABIR, SAAD
Application year: 2000
Main classification: G01L
IPC codes: G01L1, G01L5, G01L17