Patent Publication Number: US-2012025852-A1

Title: Electronic circuit for the evaluation of information from variable electric resistance sensors

Description:
FIELD OF THE INVENTION 
     The presented application deals with the electronic circuit for high-speed evaluation of information from variable electric resistance sensors, e.g. from tactile sensors on the base of conductive elastomer. 
     DESCRIPTION OF THE PRIOR ART 
     Currently with the development of robotics, automatization and non-invasive diagnostics in medicine, it is all the more necessary to obtain information on the interaction of a robot with the surrounding environment and information on the technical operations that are in progress. Scanning contact pressures belongs to important characteristics of interaction between the systems or their parts. For example, pressure distribution in a tyre in contact with the road surface, conveyor belts, their even stress. It is very important to establish the distribution of pressures in biomechanics between a living organism and the surrounding environment when the pathological distribution of pressures can cause very serious health problems. Likewise, pressure distribution can lead to non-invasive diagnostics of various diseases or to the defect of skeletal-muscular system in humans. 
     Present systems most frequently use tactile sensors which utilize piezoresistive materials, piezoresistive foils or conductive elastomers working as a pressure to electric signal transducer. Present sensors on the base of a conductive elastomer utilize scanning voltage or current from an appropriate tactile element for measuring contact pressure surface distribution. The signal is then conducted to a multiplexor and an analogue-to-digital converter, digitalized and further processed. Disadvantages of this solution are the necessity to use a multiplexor for switching over the measured channel, the small speed of scanning the arrangement of contact pressure given by using one analogue-to-digital converter, or possibly only a few analogue-to-digital converters, large power consumption, the dependence of the consumption of the device on the magnitude of pressure at individual points of the tactile sensor, or the high cost of electronic equipment given by the high cost of a very fast analogue-to-digital converter. 
     SUMMARY OF THE INVENTION 
     Above-mentioned disadvantages are eliminated by an electronic circuit for high-speed information evaluation from variable electric resistance sensors, where this sensor is formed by a matrix composed of columns and rows according to the presented solution. Its principle is that to at least one row and one column of the matrix a circuit is connected, which is formed by a parallel capacitor and resistor combination to which a row switch is connected in series. In addition to this parallel combination a serial combination of a sensor with variable electric resistance and a column switch is attached. Thus formed, the connection of elements is connected to a power supply. The common point of the parallel combination of a capacitor and resistor is interconnected over a wave-shaping circuit with a counter. The row switch is connected to one output terminal of a timing block, to the other output terminal the column switch is connected. 
     In one possible implementation a protection block is inserted to the serial combination of the variable electric resistance sensor and the column switch, namely between the terminal for connecting the variable electric resistance sensor and the common point of the parallel combination of capacitor and resistor. 
     In advantageous implementation the row switch can be implemented by a transistor of conductivity type P and the column switch by a transistor of conductivity type N. The wave-shaping circuit can be implemented by the integrated Schmitt flip-flop circuit. 
     Further, the circuit in advantageous implementation can be perfected with a diode for protecting parts of the circuit from external influences produced by the variable electric resistance sensors. The diode is oriented by the anode towards the resistor and by the cathode towards the sensor. 
     The presented electronic circuit enables the elimination of the analogue-to-digital converter from the measuring system and thus eliminating its high cost. Further, with its simple construction it enables forming a parallel scanning system and thus creating a high-speed one whose power consumption is not, thank to circuit timing, dependant on the magnitude of pressure of individual tactile sensors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention and its effects are explained in greater detail in the description of an example of its implementation, according to the attached drawing which represents the block diagram of the presented electronic circuit for high-speed information evaluation from variable electric resistance sensors, e.g. from tactile sensors on the base of the conductive elastomer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The electronic circuit for high-speed information evaluation from variable electric resistance sensors, where this sensor is formed by a matrix composed of columns and rows, consists of electric power supply  1 , row switch  2 , capacitor  3 , resistor  4 , wave-shaping circuit  8 , column switch  7 , counter  9 , timing block  10 . 
     To the parallel combination of capacitor  3  and resistor  4  a row switch is connected in series. Parallel to the formed combination is then connected a serial combination of variable electric resistance sensor  6  which is connected to circuit terminals, and column switch  7 . The whole connection of elements that has been formed in this way is connected to power supply  1 . The parallel combination of capacitor  3  and resistor  4  is connected to the input of wave-shaping circuit  8 , its output terminal is connected to the input of counter  9 . Row switch  2  is connected to output terminal of timing block  10  to whose other output terminal a column switch  7  is connected. 
     In the advantageous implementation, which is the simplest, row switch  2  can be implemented by a transistor with conductivity type P and column switch  7  by transistor with conductivity type N. Simultaneously, wave-shaping circuit  8  can be implemented by the integrated Schmitt flip-flop circuit. For implementation of row switch  2  and column switch  7  it is possible to use any other combination of transistors of type N or P, however, this way the circuit is made more complicated, therefore more expensive. 
     Furthermore, the advantageous circuit implementation can be completed by block  5 , protecting the circuit from outside influences coming in from the direction of variable electric resistance sensor  6 . The simplest way of protection is to incorporate a diode whose anode is oriented towards resistor  4  and cathode towards sensor  6 . 
     The working cycle of the presented circuit is divided into two phases which are controlled by timing block  10 . 
     In the first phase row switch  2  is connected, column switch  7  is disconnected. Capacitor  3 , to which resistor  4  is connected in parallel, is charged by power supply  1 . The parallel combination of capacitor  3  with resistor  4  ensures discharging of capacitor  3 , also in the case of working with disconnected or defective variable electric resistance sensor  6 . 
     In the second phase row switch  2  is disconnected, column switch  7  is connected. Through the resistance of variable electric resistance sensor  6 , capacitor  3  is discharged, with the speed of discharging dependant on the current resistance of variable electric resistance sensor  6 . The magnitude of the current resistance of variable electric resistance sensor  6  is in this way transferred to discharging time of capacitor  3 . From the parallel combination of capacitor  3  and resistor  4 , a signal is taken to wave-shaping circuit  8  which provides the transfer of the analogue signal to logical level L or H and increases noise immunity. The time period of a signal established in this way is measured by counter  9  and sent for further processing. By forming a greater number of above-described circuits for each row or, possibly, column, it is possible to substantially increase the speed of the scanning, and at the same time to reduce the costs of evaluation electronics, compared to using more parallel analogue-to-digital converters. The outcome of a circuit formed this way is the information about the value monitored from variable electric resistance sensor  6 , originally an analogue value converted to digital form. For example, in case of using a tactile sensor in place of sensor with variable electric resistance  6 , the output number from counter  9  is proportional to the force acting to the given variable electric resistance sensor  6 . The obtained digital information can be, for example, displayed on the monitor of a computer, stored on the storage medium or processed in some other way. 
     INDUSTRIAL APPLICABILITY 
     The described electronic circuit for high-speed evaluation of information from variable electric resistance sensors makes it possible to increase the speed of scanning from sensors in unison with removing the high-speed analogue-to-digital converter and thus reducing the price of the resultant device. At the same time it makes it possible to reduce power consumption, to remove the dependence of power consumption on the measured force, and it makes parallel evaluation possible for a great number of parallel rows and columns of a sensor. 
     In combination with, e.g., a proportional pressure distribution sensor it is applicable to the field of medical orthopaedics and biomechanics for studying pressure distribution on the soles of feet and its dynamic changes during a step. Determining pressure distributions on the soles of feet and their time progress is valuable information contributing to non-invasive diagnostics of motoric activity defects, orthopaedic defects and a number of other disorders, as well as contributing to preventing pathological pressures on a human body causing bedsores, e.g. an intelligent bed. In stabilometry the mentioned sensors can be used for measuring stability, they can be used in physiotherapy, for developing therapy aids and artificial limbs and also for biological feedback, so-called biofeedback. The circuit is also applicable for designing anatomical shapes of seats and back rests, especially in automobile and aircraft industries. Practical use can also be found in sports medicine and methodology, in robotics for stability and balancing of robots, for determining the fixed point of grip, determining force, etc. and in other industrial applications where the knowledge of pressure distribution is required, e.g. tyre—road surface.