Patent Publication Number: US-2020285596-A1

Title: Switch device

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present patent application claims the priority of Japanese patent application No. 2017-190714 filed on Sep. 29, 2017, and the entire contents of Japanese patent application No. 2017-190714 are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a switch device. 
     BACKGROUND ART 
     An input device is known in which a fingerprint recognition sensor is mounted on at least one of plural push switches, the fingerprint recognition sensor reading fingerprint data to perform a verification by comparison between the read fingerprint data and a pre-enrolled fingerprint data to identify an individual based on the verification result, and a control unit performs verification when the push switch with the fingerprint recognition sensor is pushed down and thereby the control unit detects a push signal generated and transmitted therefrom (see, e.g., Patent Literature 1). 
     The input device is configured such that appropriate fingerprint data is easily read by the fingerprint recognition sensor to suitably perform the verification of fingerprint. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2006/155455 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     The input device disclosed in Patent Literature 1 may fail in a verification depending on the touch position of the finger or the condition of the finger even when an operation is performed by an enrolled operator. In this case, if a false acceptance rate thereof is increased, the verification may be loosened but the security level may decrease. If the security level is increased, the verification may be tightened and thus may be failed even when the enrolled operator operates, causing a decrease in usability. 
     It is an object of the invention to provide a switch device which can provide improved usability while ensuring the security level. 
     Solution to Problem 
     According to an embodiment of the invention, a switch device comprises a verification unit, wherein the verification unit calculates a degree of similarity between biometric information read by a biometric information sensor and enrolled biometric information enrolled beforehand, wherein if the degree of similarity is not less than a verification threshold, the verification unit determines that verification is successful, and wherein if the degree of similarity is smaller than the verification threshold and not less than the first threshold, the verification unit sets as a new verification threshold a second threshold larger than a first threshold and smaller than the verification threshold. 
     According to an embodiment of the invention, it is possible to provide a switch device which can provide improved usability while ensuring the security level. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a perspective view showing a start switch device in an embodiment. 
         FIG. 1B  is a front view showing the start switch device in the embodiment. 
         FIG. 2A  is a block diagram illustrating the start switch device in the embodiment. 
         FIG. 2B  is a graph showing degree of similarity and occurrence rate. 
         FIG. 3  is a flowchart showing an operation of the start switch device in the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Summary of the Embodiment 
     A switch device in the embodiment has a verification unit that calculates a degree of similarity between biometric information sensor read by a biometric information sensor and enrolled biometric information enrolled beforehand, determines that verification is successful when the degree of similarity is not less than a verification threshold, and sets a second threshold larger than a first threshold and smaller than the verification threshold as a new verification threshold when the degree of similarity is smaller than the verification threshold and not less than the first threshold. 
     Even when verification fails at the first verification attempt, the switch device can set a new verification threshold lower than the verification threshold while ensuring the security level, hence, it is possible to improve usability while ensuring the security level, unlike when the verification threshold is fixed. 
     Embodiment 
     (General Configuration of Start Switch Device  1 ) 
       FIG. 1A  is a perspective view showing a start switch device in an embodiment and  FIG. 1B  is a front view showing the start switch device in the embodiment.  FIG. 2A  is a block diagram illustrating the start switch device in the embodiment, and  FIG. 2B  is a graph showing degree of similarity and occurrence rate. In each drawing of the embodiment described below, a scale ratio may be different from an actual ratio. In addition, in  FIG. 2A , flows of main signals and information are indicated by arrows. 
     The start switch device  1  as the switch device is provided with, e.g., an operation button  2  having an operation surface  20  to be push-operated, a biometric information sensor  3  arranged on the operation button  2  so that a reading surface  30  for reading biometric information S 1  is exposed on the operation surface  20 , a switch unit  4  which detects a push operation performed on the operation button  2 , and a control unit  9  as the verification unit, as shown in  FIGS. 1A, 1B, 2A and 2B . 
     The control unit  9  of the start switch device  1  is configured to calculate a degree of similarity between the biometric information S 1  read by the biometric information sensor  3  and enrolled biometric information  90  which has been enrolled beforehand, to determine that verification is successful when the degree of similarity is not less than a verification threshold  91 , and to set a second threshold  93  larger than a first threshold  92  and smaller than the verification threshold as a new verification threshold  91  when the degree of similarity is smaller than the verification threshold  91  and not less than the first threshold  92 . 
     When the degree of similarity between the next read biometric information S 1  and the enrolled biometric information  90  is not less than the new verification threshold  91  (=the second threshold  93 ), the control unit  9  determines that verification is successful and the operator is the enrolled individual. 
     Meanwhile, the control unit  9  is also configure to not set a new verification threshold  91  when the degree of similarity is smaller than the first threshold  92 , based on the determination that verification is failure. 
     When verification of the biometric information S 1  is successful and the switch unit  4  is in the on state, the control unit  9  outputs an instruction signal S 3  to give an instruction to start a drive system of a vehicle. 
     In detail, as an example, the start switch device  1  is configured that the biometric information sensor  3  can read the biometric information S 1  after doors are unlocked upon authentication based on wireless communication with an electronic key, etc., and drive voltage is supplied from a battery of the vehicle. 
     In the vehicle, the drive system is started based on the instruction signal S 3  which is output when the switch unit  4  is turned on by a push operation and verification of the biometric information S 1  is successful. 
     The drive system is, e.g., an internal combustion engine, a motor, or a combination thereof, etc. The start switch device  1  is configured to give an instruction to start/stop the drive system. 
     (Configuration of the Operation Button  2 ) 
     The operation button  2  is arranged, e.g., inside a cylindrical body  10  as shown in  FIGS. 1A and 1B . A bezel  12  is attached to an end of the body  10  and the operation surface  20  of the operation button  2  is exposed in an opening  120  of the bezel  12 . The switch unit  4  is arranged on an end portion of the operation button  2  on the opposite side to the operation surface  20 . 
     (Configuration of the Biometric Information Sensor  3 ) 
     The biometric information sensor  3  is arranged at the center of the operation surface  20  of the operation button  2 . The biometric information sensor  3  is configured that the reading surface  30  for reading the biometric information S 1  has a rectangular shape and is exposed on the operation surface  20 . The position of the reading surface  30  is, e.g., lower than the operation surface  20 . 
     The biometric information sensor  3  is configured to read the biometric information S 1  of an operating finger in contact with the operation surface  20 . As an example, the biometric information S 1  includes image information of at least one of fingerprint pattern and vein pattern of the operating finger. 
     When configured to read, e.g., a fingerprint pattern, the biometric information sensor  3  is constructed from an optical, capacitive, electric field strength measuring, pressure-sensitive, or thermal sensor. 
     Meanwhile, when configured to read, e.g., a vein pattern, the biometric information sensor  3  is configured to read a vein pattern based on reflection of infrared radiation. 
     As an example, the biometric information sensor  3  in the present embodiment is a capacitive sensor which reads a fingerprint pattern. The biometric information sensor  3  outputs the read fingerprint pattern, as the biometric information S 1 , to the control unit  9 . 
     (Configuration of the Switch Unit  41 ) 
     The switch unit  4  is a switch to be turned on by displacement of the operation button  2  due to a push operation, and is configured to be turned off when a load due to the push operation is removed. 
     When turned on, the switch unit  4  outputs a switch signals S 2  to the control unit  9 . When the switch signals S 2  is input, the control unit  9  determines that a push operation is performed. 
     (Configuration of the Control Unit  9 ) 
     The control unit  9  is, e.g., a microcomputer composed of a CPU (Central Processing Unit) performing calculation and processing, etc., of the acquired data according to a stored program, and a RAM and a ROM (Read Only Memory) which are semiconductor memories. The ROM stores, e.g., a program for operation of the control unit  9 , the enrolled biometric information  90 , the verification threshold  91 , the first threshold  92  and the second threshold  93 , The RAM is used as, e.g., a storage area for temporarily storing calculation results, etc. 
     As an example, the control unit  9  determines that an operator is the enrolled individual when the degree of similarity between the characteristic features of the fingerprint pattern of the operator based on the biometric information S 1  acquired from the biometric information sensor  3  and the characteristic features of the fingerprint pattern of the enrolled individual contained in the enrolled biometric information  90  is greater than the verification threshold  91 . 
     When, e.g., it is determined that the operator is the enrolled individual and it is also determined based on an input of the switch signals S 2  that the switch unit  4  is in the on state, the control unit  9  generates the instruction signal S 3  to give an instruction to start the drive system and outputs the instruction signal S 3  to a vehicle control unit, etc. 
     Now referring to  FIG. 2B , the distribution on the left represents imposter data similarity distribution and the distribution on the right represents genuine data similarity distribution. In  FIG. 2B , the horizontal axis indicates the degree of similarity and the vertical axis indicates the occurrence rate. In the region in which the two distributions overlap, the area on the left side of the verification threshold  91  (the area shaded with diagonal lines sloping down to the right) is the False Rejection Rate (FRR) and the area on the right side (the area shaded with diagonal lines sloping up to the right) is the False Acceptance Rate (FAR). 
     When the verification threshold  91  is changed to a value on the right side on the paper of  FIG. 2B , the security level is improved due to stricter verification but the usability decreases. The decrease in usability means that there is more likelihood that the biometric information S 1  will need to be read several times since successful verification does not occur without a high degree of similarity, and this decreases convenience. 
     Meanwhile, when the verification threshold  91  is changed to a value on the left side on the paper  FIG. 2B , usability is improved due to easier verification but the security level decreases. As such, the security level and the usability are in a trade-off relation. 
     Thus, in the present embodiment, when, e.g., the degree of similarity at the first verification attempt is smaller than the verification threshold  91  and not less than the first threshold  92 , the control unit  9  uses the second threshold  93  as a new verification threshold  91  (=the second threshold  93 ) for the next verification and onward. This means that verification at the first verification attempt is failure. 
     Then, the control unit  9  calculates the degree of similarity between the next read biometric information S 1  and the enrolled biometric information  90 , and when this degree of similarity is not less than the newly set verification threshold  91  (=the second threshold  93 ), the control unit  9  determines that the operator is the enrolled individual. Meanwhile, when this degree of similarity is smaller than the first threshold  92 , the control unit  9  determines that verification is failure. Furthermore, when this degree of similarity is not less than the first threshold  92  and smaller than the verification threshold  91  the second threshold  93 ), the control unit  9  calculates the degree of similarity between the further next biometric information S 1  and the enrolled biometric information  90  and performs verification using the verification threshold  91  (=the second threshold  93 ). 
     In a modification of verification, for example, the number of retries within a certain period of time may be set, or a time limit for retries may be set. For example, the control unit  9  counts and measures the number of performed verification attempts and the elapsed time since the first verification attempt, and when the number of retries exceeds the limit, the control unit  9  stops performing verification even still in time. Meanwhile, when, e.g., a time limit is set, the control unit  9  measures time from the first verification attempt and stops performing verification when exceeding the time limit. The stop of verification may be, e.g., suspension of verification for a certain period of time, suspension continued until cancellation of the suspension, or stop of performing verification with the new verification threshold  91  and back to verification with the original verification threshold  91 . In the present embodiment, when exceeding the time limit, verification with the new verification threshold  91  is stopped and verification is performed with the original verification threshold  91 . 
     The control unit  9  preferably sets the new verification threshold  91  the second threshold  93 ) within, e.g., the range of the false rejection rate defined by the verification threshold  91 , as shown in  FIG. 28 . The range of the false rejection rate is, e.g., the range indicated by diagonal lines sloping down to the right on the paper of  FIG. 2B . This is because if the second threshold  93  is out of the range of the false rejection rate and has a value with a low degree of similarity, the security level significantly decreases as compared to when within the range. 
     Next, an example of an operation of the start switch device  1  in the present embodiment to start the drive system will be described in reference to the flowchart of  FIG. 3 . 
     (Operation) 
     The of the control unit  9  of the start switch device  1  determines that a push operation is performed when it is “Yes” in Step  1 , i.e., when the switch signals S 2  is input from the switch unit  4  (Step  1 : Yes). 
     Then, based on the biometric information S 1  read at the time of the push operation and the enrolled biometric information  90 , the control unit  9  calculates the degree of similarity (Step  2 ). After that, when the calculated degree of similarity is not less than the verification threshold  91  (Step  3 : Yes), the control unit  9  determines that verification is successful, and the control unit  9  outputs the instruction signal S 3  to give an instruction to start the drive system (Step  4 ). 
     When verification is failure in Step  3  (Step  3 : No), the control unit  9  compares the degree of similarity with the first threshold  92 . When the degree of similarity is not less than the first threshold  92  (Step  5 : Yes), the control unit  9  sets the second threshold  93  as a new verification threshold  91  (Step  6 ), and the process proceeds to Step  1  to monitor whether a push operation is performed or not. 
     The control unit  9  changes back to the original verification threshold  91  when, e.g., a push operation is not determined or verification is failure within a predetermined time limit after setting the second threshold  93  as a new verification threshold  91 . 
     When the degree of similarity is smaller than the first threshold  92  in Step  5  (Step  5 : No), the control unit  9  determines failure of verification and terminates verification (Step  7 ). 
     Regarding determination of push operation and verification, verification is performed after the push operation is determined in the above example, but it is not limited thereto. For example, the push operation may be determined after successful verification. 
     Meanwhile, when stopping the drive system, the start switch device  1  is triggered by an input of the switch signals S 2  and outputs the instruction signal S 3  for stopping the drive system, without performing verification of the biometric information S 1 . 
     Effects of the Embodiment 
     The start switch device  1  in the present embodiment can provide improved usability while ensuring the security, in detail, even when verification fails at the first verification attempt, the start switch device  1  can set a new verification threshold  91  the second threshold  93 ) lower than the verification threshold  91  while ensuring the security, as long as the degree of similarity is not less than the first threshold  92 . Therefore, the start switch device  1  can improve usability while ensuring the security, unlike when the verification threshold is fixed. 
     The start switch device  1  can lower the verification threshold  91  when the first verification attempt fails and the degree of similarity is not less than the first threshold  92 . Therefore, probability of successful verification at the next push operation is increased as compared to when not lowered. In addition, the start switch device  1  does not lower the verification threshold  91  when the degree of similarity is smaller than the first threshold  92 . Therefore, unlike when such a configuration is not adopted, it is possible to prevent unenrolled individuals from internationally lowering the verification threshold  91  by continuously performing the push operations. 
     The start switch device  1  sets the second threshold  93  to be a new verification threshold  91  within the range of the false rejection rate. Therefore, unlike when such a configuration is not adopted, it is possible to facilitate verification while maintaining the security level. 
     As a modification, the verification threshold  91  may be changed between plural thresholds, in addition to the second threshold  93 . 
     Although some embodiment and modifications of the invention have been described, the embodiment and modifications are merely an example and the invention according to claims is not to be limited thereto. The new embodiment and modifications may be implemented in various other forms, and various omissions, substitutions and changes, etc., can be made without departing from the gist of the invention. In addition, all combinations of the features described in the embodiment and modifications are not necessary to solve the problem of the invention. Further, the embodiment and modifications are included within the scope and gist of the invention and also within the invention described in the claims and the range of equivalency. 
     REFERENCE SIGNS LIST 
     
         
           1  START SWITCH DEVICE 
           2  OPERATION BUTTON 
           3  BIOMETRIC INFORMATION SENSOR 
           4  SWITCH UNIT 
           9  CONTROL UNIT 
           20  OPERATION SURFACE 
           30  READING SURFACE 
           90  ENROLLED BIOMETRIC INFORMATION 
           91  VERIFICATION THRESHOLD 
           92  FIRST THRESHOLD 
           93  SECOND THRESHOLD