Thickness detecting caliper for sheet material having elastic arms with printed coils

Abstract

A pair of elastic strips are provided in order to hold sheet material to be measured in thickness. Each of the elastic strips includes of one or more elastic films. Ends of the elastic strips are supported by support portions, and the other ends of the elastic strips are provided with respective coils, opposed to push each other, and kept in contact with each other. When the sheet material is held between support portions, the inductances of the coils are changed and the thickness of the sheet material is detected as an electric signal representative of the changed inductance.

1. A thickness detector comprising:
 first and second elastic strips, respective first end portions of each strip being fixedly supported and second end portions thereof being (i) arcuately disposed in biased opposition to each other and (ii) configured to detect a thickness of an object being conveyed therebetween, each second end portion having a coil attached thereto; and  
 measurement means for measuring a clearance between the first and  second end portions, the clearance being representative of the thickness of the object, the measuring detecting a mutual inductance between the coils.  
 
     
     
       2. A detector according to  claim 1 , wherein each of the elastic strips includes two or more elastic films adhered to each other by an adhesive member which functions as a damping material. 
     
     
       3. A detector according to  claim 2 , wherein each of the coils includes coil members provided respectively on both sides of one of the elastic films. 
     
     
       4. A detector according to  claim 2 , wherein each of the coils includes printed coils provided respectively on both sides of one of the elastic films. 
     
     
       5. A detector according to  claim 2 , wherein each of the coils includes printed coils provided respectively on both sides of one of the elastic films and connected to each other by a through-hole. 
     
     
       6. A detector according to  claim 1 , wherein the coils are connected in series with each other and cooperatively function as a detection coil, and wherein the measurement means includes:
 a bridge circuit having a first resistor connected in series with the detection coil, a second resistor having a resistance equal to that of the first resistor, and a dummy coil connected in series with the second resistor and having an inductance which is equal to the inductance of the detection coil when the end portions of the elastic members contact with each other;  
 a differential amplifier having a first input connected to a connection portion between the detection coil and the first resistor, and a second input connected to a connection portion between the dummy coil and the second resistor;  
 an oscillator for supplying a sine wave to the bridge circuit; and  
 means for outputting a signal representing the thickness of the object, using an output of the differential amplifier.  
 
     
     
       7. A detector according to  claim 6 , wherein the measurement means further includes a balance adjust resistor for adjusting a balance between an impedance created by the first resistor and the detection coil and an impedance created by the second resistor and the dummy coil. 
     
     
       8. A detector according to  claim 1 , wherein a wear-resistance member is provided on a surface of each of the elastic members is brought into contact with the object sliding thereon. 
     
     
       9. A detector according to  claim 8 , wherein the wear-resistance member is made of ceramics. 
     
     
       10. A detector according to  claim 8 , wherein the wear-resistance member is a diamond-like carbon film. 
     
     
       11. A detector according to  claim 1 , wherein a plurality of pairs each including the first and second strips are provided in a direction perpendicular to a conveyance direction in which the object is conveyed. 
     
     
       12. A thickness detector for detecting a thickness of an object to be measured, which is conveyed along a conveyer path, comprising:
 first and second elastic members each including double-coated tape having a damping function, first elastic film adhered onto first surface of the double-coated tape that is opposite to second surface thereof opposite to the first surface and facing the conveyer path, second elastic film adhered onto the second surface of the double-coated tape facing the conveyer path, wear-resistance member provided at end portion of the second elastic film on the surface thereof facing the conveyer path thereby to prevent wear caused by the object being conveyed along the conveyer path, and first and second coils provided on both surfaces of end portion of the first elastic film and connected in series with each other, the first and second elastic members having other ends fixed such that the end portions elastically push each other; and  
 detection means for outputting a detection signal corresponding to the thickness of the object being conveyed, based on a serial inductance created by the first and second coils of the first elastic member and the first and second coils of the second elastic member.  
 
     
     
       13. A detector according to  claim 12 , wherein the coil of each of the elastic members includes printed coils provided respectively on both sides of the first elastic film. 
     
     
       14. A detector according to  claim 12 , wherein the coil of each of the elastic members includes printed coils provided respectively on both sides of the first elastic film and connected to each other by a through-hole. 
     
     
       15. A detector according to  claim 12 , wherein the coils provided at the top end portions of the elastic members are connected in series with each other, functioning as a detection coil, and the detection means includes:
 a bridge circuit having a first resistor connected in series with the detection coil, a second resistor having a resistance equal to that of the first resistor, and a dummy coil connected in series with the second resistor and having an inductance which is equal to that of the detection coil when the end portions of the elastic members contact with each other;  
 a differential amplifier having a first input connected to a connection portion between the detection coil and the first resistor, and a second input connected to a connection portion between the dummy coil and the second resistor;  
 an oscillator for supplying a sine wave to the bridge circuit; and  
 means for outputting a signal representing the thickness of the object, using an output of the differential amplifier.  
 
     
     
       16. A detector according to  claim 15 , wherein the detection means further includes a balance adjust resistor for adjusting a balance between an impedance created by the first resistor and the detection coil and an impedance created by the second resistor and the dummy coil. 
     
     
       17. A detector according to  claim 12 , wherein the wear-resistance members are made of ceramics. 
     
     
       18. A detector according to  claim 12 , wherein the wear-resistance members are diamond-like carbon films. 
     
     
       19. A detector according to  claim 12 , wherein a plurality of pairs each including the pair of elastic members are provided in a direction perpendicular to a conveyance direction in which the object is conveyed.