Abstract:
A method for manufacture of a pressure sensing mat comprising the steps of: (a) preparing two conductive layers, each conductive layer comprising an array of conducting strips mounted upon a substrate arranged in a parallel fashion, wherein the conducting strips of the first conductive layer are oriented perpendicularly in relation to the conducting strips of the second conductive layer; (b) for each conductive layer, connecting each of the conducting strips to a communication line; (c) sandwiching a compressible layer between the two conductive layers; and (d) performing a pressure reading standardization test to the mat.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase of PCT Appln. No. PCT/IB2012/053538 filed Jul. 11, 2012 which claims the benefit of U.S. Provisional Application No. 61/507,418 filed Jul. 13, 2011, the disclosures of which are incorporated in their entirety by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The embodiments disclosed herein relate to pressure sensing mats, in particular the disclosure relates to the manufacture and system testing of a pressure sensing mat comprising crossed parallel strip electrodes forming a pressure sensing matrix. 
     BACKGROUND 
     A pressure sensing mat comprising crossed parallel strip electrodes forming a pressure sensing matrix is described for example in the applicant&#39;s copending PCT patent application number PCT/IL2010/000294 although the current disclosure may be applicable to other sensing mats. 
     Where pressure sensing mats are used it is important to ensure equipment meets quality standards. It will be appreciated that there is therefore a need for a method of manufacture which integrates construction with continued quality assurance and system testing. The disclosure herein addresses this need. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the current disclosure, a method is presented for the manufacture of a pressure sensing mat, the method comprising the steps of: (a) preparing two conductive layers, each conductive layer comprising an array of conducting strips mounted upon a substrate arranged in a parallel fashion, wherein the conducting strips of the first conductive layer are oriented perpendicularly in relation to the conducting strips of the second conductive layer; (b) for each conductive layer, connecting each of said conducting strips to a communication line; (c) sandwiching a compressible layer between said two conductive layers; and (d) performing a pressure reading standardization test to said mat. 
     In certain embodiments, the conductive strips are laminated with an insulating material. 
     In certain embodiments, the step of preparing two conductive layers, step (a) above, comprises the steps of: (i) affixing said conductive strips to a substrate in a parallel orientation; and (ii) measuring the resistance between at least one pair of adjacent conductive strips. 
     In certain embodiments, the conductive strips are connected to a test monitor through a test probe. Alternatively, two of said conductive strips are connected to a test monitor through a test probe, and the test probe is moved sequentially from one pair of adjacent conductive strips to the next until all the strips have been tested. 
     In certain embodiments, the step of, for each conductive layer, connecting each of said conducting strips to a communication line, step (b) above, is followed by a testing procedure comprising the steps of: (i) placing a conducting plate across said conducting strips; (ii) applying an alternating potential to said conducting plate; and (iii) measuring voltage between each of the conducting strips and ground. 
     In certain embodiments, the step of, for each conductive layer, connecting each of said conducting strips to a communication line, step (b) above, is followed by a testing procedure comprising the steps of: (i) placing a conducting plate across said conducting strips; (ii) applying an alternating potential to each of said conducting strips; and (iii) for each conducting strip measuring voltage between the conducting plate and ground. 
     In certain embodiments, the step of, for each conductive layer, connecting each of said conducting strips to a communication line, step (b) above, is followed by a testing procedure comprising the steps of: (i) placing a conducting plate across said conducting strips; (ii) applying an alternating potential to all conducting strips except one selected conducting strip; and (iii) measuring voltage between the selected strip and ground. 
     In certain embodiments, the step of, for each conductive layer, connecting each of said conducting strips to a communication line, step (b) above, is followed by a testing procedure comprising the steps of: (i) placing a conducting plate across said conducting strips; (ii) applying an alternating potential to one selected conducting strip; and (iii) measuring voltage between all conducting strips except the selected strip and ground. 
     In certain embodiments, the conducting plate is laminated with an insulating material. 
     In certain embodiments, the step of performing a pressure reading standardization test to said mat, step (d) above, comprises the steps of: (i) exerting a known pressure upon at least one region of said pressure detection mat; (ii) measuring a pressure reading recorded by said pressure detection mat; and (iii) comparing said pressure reading with a look up table. 
     According to a second aspect of the current disclosure, a method is disclosed for testing a pressure sensing mat comprising a first conductive layer comprising an array of parallel conducting strips, a compressible layer situated upon the first array and a second conductive layer comprising an array of parallel conducting strips situated upon the compressible layer, the conducting strips of each conductive layer being connected to a communication line, the method comprising the step of: (a) for each conductive layer, measuring the resistance between at least one pair of adjacent conducting strips. 
     In certain embodiments, the conductive strips are laminated with an insulating material. 
     In certain embodiments, for the step of, for each conductive layer, measuring the resistance between at least one pair of adjacent conducting strips, step (a) above, each of said conductive strips is connected to a test monitor through a test probe. Alternatively, two of said conductive strips are connected to a test monitor through a test probe, and the test probe is moved sequentially from one pair of adjacent conductive strips to the next until all the strips have been tested. 
     In certain embodiments, the method of testing the pressure sensing mat further comprises the step of: (b) testing the electrical connection between each of said conducting strips and the communication line. 
     Optionally, step (b) comprises the steps of: (i) placing a conducting plate across said conducting strips; (ii) applying an alternating potential to said conducting plate; and (iii) measuring voltage between each of the conducting strips and ground. 
     Optionally, step (b) comprises the steps of: (i) placing a conducting plate across said conducting strips; (ii) applying an alternating potential to each of said conducting strips; and (iii) for each conducting strip measuring voltage between the conducting plate and ground. 
     Optionally, step (b) comprises the steps of: (i) placing a conducting plate across said conducting strips; (ii) applying an alternating potential to all conducting strips except one selected conducting strip; and (iii) measuring voltage between the selected strip and ground. 
     Optionally, step (b) comprises the steps of: (i) placing a conducting plate across said conducting strips; (ii) applying an alternating potential to one selected conducting strip; and (iii) measuring voltage between all conducting strips except the selected strip and ground. 
     In certain embodiments, the method of testing the pressure sensing mat further comprises the step of: (c) performing a pressure reading standardization test to said mat. 
     Optionally, step (c) comprises the steps of: (i) exerting a known pressure upon at least one region of said pressure detection mat; (ii) measuring a pressure reading recorded by said pressure detection mat; and (iii) comparing said pressure reading with a look up table. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       For a better understanding of the embodiments and to show how it may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings. 
       With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of selected embodiments only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects. In this regard, no attempt is made to show structural details in more detail than is necessary for a fundamental understanding; the description taken with the drawings making apparent to those skilled in the art how the several selected embodiments may be put into practice. In the accompanying drawings: 
         FIG. 1  is an exploded isometric projection schematically representing an embodiment of a pressure-detection mat; 
         FIG. 2  is a flowchart of a method of manufacture and system testing of a pressure sensing mat; 
         FIG. 3A  is a schematic representation of one possible layer of a pressure sensing mat during preparation; 
         FIG. 3B  is a schematic representation of a possible test probe for use testing the electrical isolation of conductive strips of the pressure sensing mat; 
         FIGS. 3C  and D show the test probe being used to test the pressure sensing mat; 
         FIG. 3E  is a schematic representation of another possible test probe; 
         FIG. 4  is a schematic representation of an embodiment of the layer including the conducting strips and a controller communication line; 
         FIGS. 5A-C  show various methods for testing the connections between the conducting strips and the controller communication line; and 
         FIG. 6  is a top view of an embodiment of a pressure sensing module incorporated into a mattress overlay. 
     
    
    
     DETAILED DESCRIPTION 
     Reference is now made to  FIG. 1  which shows an exploded isometric projection schematically representing an embodiment of a pressure-detection mat  200  comprising a plurality of sensors  210  arranged in a form of a matrix. The mat  200  of the embodiment includes two arrays  220 A,  220 B of conductive strips  222 ,  224  affixed on a substrate  240 A,  240 B, two controller communication lines  225 A,  225 B and a compressible layer  230 . Each conductive strip  222 ,  224  may be laminated with an insulating material. The compressible layer  230  may comprise an insulating, compressible material. 
     The two conductive layers  220 A,  220 B made of conductive material are separated by the compressible layer  230 . Each of the conductive layers  220 A,  220 B typically consists of an array of parallel conductive strips  222 ,  224  (respectively). Further, the two arrays may be arranged orthogonally such that in the first conductive layer  220 A, the array of conductive strips  222  are horizontal and in the second conductive layer  220 B, the array of conductive strips  224  are vertical. It is particularly noted that each conducting strip  222 ,  224  is insulated from, and not in conductive contact with, other conducting strips in its respective layer. 
     The controller communication lines  225 A,  225 B provide a line of communication between the sensors  210  and a system controller (not shown). Each of the conductive strips  222 ,  224  may be connected to a controller communication line  225 A,  225 B via an individual connector  227 . Optionally, the communication lines  225 A,  225 B may comprise a bundle of conductors such as a multi-core cable, a flat cable or the like. 
     Each sensor  210  may be a capacitance sensor based upon the capacitance between the overlapping sections of the conducting strips at each junction of a vertical conductive strip  222  with a horizontal conductive strip  224 . These capacitance sensors are configured such that pressing anywhere on their surface changes the spacing between the two conductive layers  220 A,  220 B, and consequently the capacitance of the intersection. A controller may provide an electric potential selectively to each vertical strip via a first communication line  225 A and the electrical potential may be monitored on each horizontal strip via a second communication line  225 B such that the capacitance of the sensor  210  of the overlapping section may be determined. 
     It is noted that by providing an oscillating electric potential across each sensor and monitoring the alternating current produced thereby, the impedance of the intersection may be calculated and the capacitance of the intersection determined. The alternating current varies with the potential across a capacitor according to the formula:
 
I ac =2πfCV ac  
 
where I ac  is the root mean squared value of the alternating current, V ac  is the root mean squared value of the oscillating potential across the capacitor, f is the frequency of the oscillating potential and C is the capacitance of the capacitor.
 
     Thus where the values of V ac  and I ac  are known at a known frequency f, the capacitance C of a sensor may be calculated. Accordingly, where the mechanical properties of the sensor are known, the pressure applied upon the sensor may be deduced. 
     It will be appreciated that during the manufacture and initialization of a pressure detection mat such as described hereinabove, there is a need to ensure that each conducting strip is electrically isolated from the other conducting strips and electrically connected to the communication lines. Furthermore, the relationship between capacitance values determined for the sensors and the pressure exerted upon the mat should be determined. 
     The disclosure hereinbelow presents possible systems and methods for the manufacture and system testing of a pressure sensing mat. 
     Referring now to the flowchart of  FIG. 2 , a method of manufacture and system testing of a pressure sensing mat is presented. The method includes four phases: 
     I. Conductive Strip Preparation 
     II. Communication Line Preparation 
     III. Pressure Mat Assembly 
     IV. Pressure Reading Standardization 
     During the Conductive Strip Preparation phase, the conductive strips  222 ,  224  may be affixed to a substrate I 1  and tested for stray connections which may form short circuits between adjacent strips I 3 . The substrate may be formed from a variety of suitable materials, such as a sheet of fabric, polymer, plastic, leather, thermo poly urethane (TPU) or the like. Optionally, the conductive strips may be laminated I 2  to improve electrical insulation and to protect the conductors. One possible system for testing the electrical isolation of the conductive strips is described hereinbelow in relation to  FIGS. 3A-D . 
     During the Communication Line Preparation phase, a communication line  225 A,  225 B may be affixed to the substrate II 1 , connected to the conductive strips  222 ,  224 , II 2  and the connections tested II 3 . Possible systems for testing the connections between the communication line and the conducting strips are described hereinbelow in relation to  FIGS. 5A and 5B   
     During the Pressure Mat Assembly phase III, a compressible layer, such as a sheet of foam, or some such spongy material is sandwiched between two prepared layers having crossed conductive strips. Where required, the layers may be sewn together; alternatively, the layers may be left unsewn until after the Pressure Reading Standardization phase. 
     During the Pressure Reading Standardization phase, known pressures may be applied to the assembled pressure mat IV 1  and electrical readings recorded IV 2 . In this way, the electrical readings of the mat may be calibrated to pressure measurements IV 3 . Alternatively or additionally, thereby the mat may be tested to conform to predefined standards IV 4 . Possible standardization tests are described hereinbelow. 
     Reference is now made to  FIG. 3A  which schematically represents an embodiment of one conductive layer  10  of a pressure sensing mat during the Conductive Strip Preparation phase of manufacture. An array of conductive strips  12 A-H may be affixed to a substrate  18  with each conductive strip  12 A-H electrically isolated from its neighbors. Accordingly, the substrate  18  may be constructed from an insulating material such as fabric, polymer, plastic, leather, thermo poly urethane (TPU) or the like. 
     Referring now to  FIG. 3B , a first embodiment of a test probe  20  for use in testing the conductive layer  10  is schematically represented. Stray connections between the conductive strips  12 A-H may be identified using such a test probe  20 . The test probe  20  may include a plurality of terminals  24 , a row of probe conductors  26 A-H and a bundle of test lines  23 . The terminals  24  are connected to the probe conductors  26 A-H via dedicated test lines  23  which are optionally contained by, affixed to or otherwise secured to some platform  22 . 
     With reference to  FIG. 3C , a schematic representation is shown of the test probe  20  being used to check the isolation of the conductive strips  12 A-H of the conductive layer  10 . The test probe  20  is juxtaposed to the conductive layer  10  such that the probe conductors  26 A-H are brought into contact with the conductive strips  12 A-H. 
     A test monitor (not shown), which may comprise a processor, computer, microprocessor or other controller, may be connected to the probe  20  and operable to select and test pairs of adjacent probe terminals  24 . It will be appreciated that each pair of adjacent probe terminals  24  corresponds to a pair of adjacent conducting strips  12 . For example, in the embodiment represented in  FIG. 3C , terminals A and B correspond to conducting strips  12 A and  12 B, terminals B and C correspond to conducting strips  12 B and  12 C, terminals C and D correspond to conducting strips  12 C and  12 D, terminals D and E correspond to conducting strips  12 D and  12 E, terminals E and F correspond to conducting strips  12 E and  12 F, terminals F and G correspond to conducting strips  12 F and  12 G and terminals G and H correspond to conducting strips  12 G and  12 H. 
     Accordingly, by applying a potential difference between each selected pair of terminals and measuring the current produced thereby, the resistance between the corresponding conducting strips may be monitored. Any stray connections forming short circuits between the conducting strips may be readily detected as particularly low resistance connections. 
     Referring now to  FIG. 3D , a faulty conductive layer  10 ′ incorporating conducting strips  12 A′-H′ is represented. Most of the conducting strips of the conductive layer  10 ′ are electrically isolated, however, there is a conducting bridge  11  between two of the conducting strips  12 B′ and  12 C′. Because of this short circuit, the resistance between probe terminals B and C would be significantly lower than that between the other terminals. This would be reflected in a high current for a given potential difference applied thereacross. 
     Using such a test probe, the faulty conductive layer  10 ′ may be identified and the fault pinpointed so that it may be fixed before connection of the communication line or assembly of the pressure sensing mat. 
     It will be appreciated that although only a multi-terminal test probe is described hereinabove, various other test probes may be used as suit requirements. Referring now to  FIG. 3E , a schematic representation of an alternative test probe  20 ′ is presented in which two probe conductors  26 ′ are connected to two corresponding probe terminals  24 ′ via two test lines  23 ′. The alternative test probe  20 ′ may be used to test one pair of conducting strips  12  at a time. Current produced when a known potential difference is applied across the terminals K, L may be used to test the resistance between strips and thereby to detect short circuits. The probe  20 ′ may be moved from pair to pair sequentially until all the strips have been tested. Optionally the probe may be mechanized, perhaps using rollers, tracks, articulated arms or the like, to move between the pairs of conducting strips during the test phase. Still other embodiments of the test probe will occur to those skilled in the art. 
     Reference is now made to  FIG. 4  showing an embodiment of the conductive layer  10  including the conducting strips  12 A-H and a controller communication line  14 . The controller communication line  14 , such a multi-wire flat cable or the like, may be affixed to the conductive layer  10 , for example of TPU, following the lamination of the conducting strips  12 A-H and the testing of their electrical isolation. The controller communication line  14  includes a bundle of individual conducting wires  14 A-H for connecting the conducting strips  12 A-H to a system controller (not shown) via a set of junctions  15  such as a flat band connector or the like. Each conductor of the controller communication line  14  is connected to an associated conducting strip  12  of the conductive layer  10 . 
     In order to provide reliable communication between the controller and the pressure sensor there is a need for good electrical connection  13  between each conducting strip  12 A-H and the controller communication line  14 . Testing the quality of the connection  13  is a surprisingly difficult task, in part this is because the distal portion  16  of the conducting strips  12 A-H may be laminated or otherwise insulated. Consequently, it may not be possible to connect a probe to the distal portion  16  of the conducting strips  12 A-H. 
     In order to overcome this problem, various creative solutions are taught herein allowing the conductive connections between the strips and the communication lines to be tested. It will be appreciated that such solutions may have application beyond the scope of the pressure sensing systems such as described herein. 
     Reference is now made to  FIG. 5A  showing a possible monitoring system  30  for use in testing the connections  13  between the conducting strips  12  of the conductive layer  10  and the communication line  14 . The system  30  includes a conducting plate  32 , an insulating layer  31 , an alternating current (AC) source  34 , a switching unit  38  and a voltage monitor  36 . 
     The conducting plate  32  is laid across the conducting strips  12  and electrically isolated therefrom by an insulating layer  31 . Variously, the insulating layer  31  may be a separate sheet of insulating material, a laminate coating of the conducting plate  32 , the conducting strips  12  or combinations thereof, as suit requirements. 
     The conducting plate  32  may be wired to an AC source  34 . The switching unit  38 , such as a multiplexer for example, is connected to control communication line  14 , possibly via a flat cable connection or the like. The switching unit  38  may selectively connect each conducting strip via the controller communication line  14  to the voltage monitor  36 . 
     The conducting plate  32  forms a capacitor with each of the conducting strips  12 A-H. Thus although the conducting plate  32  is insulated from the conducting strips  12 A-H the alternating voltage applied thereto produces a significant response in the voltage monitor  36 . The voltage recorded by the system  30  may serve as an indication of quality of the connections  13  between the conducting strips  12 A-H and the control communication line  14 . If all the connections are good, the voltage monitor  36  may record similar values regardless of which conducting strip is connected thereto. Where a connection is not good, the voltage monitor may produce an anomalous record, for example not recording a voltage, recording a low voltage, recording a high voltage or the like. 
     With reference to  FIG. 5B , an alternative embodiment of the monitoring system  30 ′ may exchange the AC  34  source and the voltage monitor  36  such that the AC voltage is selectively applied to each conducting strip  12 A-H and the voltage recorded in the conducting plate  32 . 
     Referring now to  FIG. 5C , still another embodiment of the monitoring system  30 ″ is shown. One conducting strip  12 A is connected to the voltage monitor  36  and all of the other conducing strips  12 B-H are connected to the AC source  34 . A switching system (not shown) may be operable to selectively connect each conducting strip  12 A-H in turn to the voltage monitor  36  with the others connected to the AC source  34 . Anomalous voltage readings may indicate a faulty connection between the selected conducting strip  12  and the control communication line  14 . 
     Optionally, a conducting plate  32  may be placed across all the conducting strips  12 A-H which may improve voltage readings. By placing the conducting plate  32  laterally across the conducting strips, the capacitance of the overlapping area between the strip  12 A being tested and the plate  32  is relatively large in comparison with the capacitance between the associated connecting wire  14 A and the rest of the bundle  14 . Thus if the connection  13 A between one connecting wire  14 A and its associated conducting strip  12 A is broken, then the voltage reading will be significantly different from that of unbroken connections. 
     Alternatively, the capacitance between the conductive strip  12 A being tested and the other conductive strips  12 B-H may be sufficient to produce significant voltage readings. 
     It will be appreciated that the solution described in relation to  FIG. 5C  may be readily applied to testing connections in multicore cables, such as telephone lines and the like, from one end. This may be particularly useful when testing the connections with long cables where it may not be practical to connect probes both ends. Connections may be tested by connecting all cores but one to an AC voltage source and measuring the voltage produced in the remaining core. Anomalous voltage readings may be indicative of faulty connections. 
     As noted hereinabove a pressure sensing mat may be assembled by sandwiching a compressible layer, such as a sheet of foam, or some such spongy material, between two prepared conductive layers having crossed conductive strips as described hereinabove in relation to in  FIG. 1 . 
     Reference is now made to  FIG. 6 , showing a top view of an embodiment of a pressure sensing module incorporated into a mattress overlay  5000 . A sensor matrix (not shown) is housed within a cover sheet  5400  and which may be sealed by a zipper  5420  or alternatively sewn into the cover as required. The sensor module may be connected to a hardware controller (not shown) via the controller communication line (not shown). 
     The pressure detection mat  5000  may be attached to a surface in such a way that prevents movement of the mat relative to the surface. A feature of the embodiment of the mat  5000  is that the cover sheet  5400  may include a coupling mechanism for securing the mat to a seat or a back of a mattress, a bed, a chair, a bench, a sofa, a wheelchair or the like. The coupling mechanism may include for example at least one strap  5200  having an attachment means  5240  configured to secure the straps  5200  to the seat or to each other such that the pressure detection mat is held securely. This may be useful to prevent folding, wrinkling or other movement of the detection mat which may contribute to the creation of shear forces which are known to encourage the formation of external pressure sores. Suitable attachment means include for example, hook-and-eye materials such as Velcro®, buckles, adhesives, buttons, laces or the like, as suit requirements. 
     A variety of standardization tests may be performed upon the pressure detection mat  5000  for the purposes of calibration, quality assurance and the like. According to one such test, weights  42 A-E of known value and size are applied to a plurality of test points upon the mat and the responses recorded. Optionally, between three to ten test points may be tested for standard testing. In one example, six test points are selected and weights no smaller than the size of one pixel of the sensor matrix are applied thereupon. 
     According to requirements, the standardization tests may be carried out before the pressure sensing matrix is sewn into the overlay. Alternatively or additionally standardization tests may be carried out after the sensing matrix is sewn into the overlay. 
     Pressure may be applied, for example, and progressively more weights may be placed upon the mat until, say, five sample pressure values have been tested for each test point. Alternatively, in other embodiments, a mechanical mechanism such as a spring, hydraulic cylinder, pneumatic cylinder or the like, may apply a known force upon a pressing member urged onto the pressure detection mat. Still other pressure application methods will occur to those skilled in the art. 
     The readings, thus produced, may be used variously for calibration of the particular mat or to check the mats conformity to standards. For example a look up table may be compiled to calibrate the particular mat. Accordingly, calibration data may be stored for reference by a controller associated with that mat. Alternatively, the readings may be compared to a precompiled look-up table to check if they lie within a certain tolerance of the data values in that table. 
     The scope of the disclosed subject matter is defined by the appended claims and includes both combinations and sub combinations of the various features described hereinabove as well as variations and modifications thereof, which would occur to persons skilled in the art upon reading the foregoing description. 
     In the claims, the word “comprise”, and variations thereof such as “comprises”, “comprising” and the like indicate that the components listed are included, but not generally to the exclusion of other components.