Abstract:
A contact sensing device includes: a first electrode and a second electrode facing each other, a drive detection circuit of an electrostatic capacitance type, a first switching circuit that implements switching between connection and disconnection between the first electrode and ground, and a second switching circuit that implements switching between connection and disconnection between the first electrode and the second electrode. The drive detection circuit implements switching between a first state and a second state and detects an electrostatic capacitance change in the first state and an electrostatic capacitance change in the second state.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a contact sensing device that is mounted on a door handle of a vehicle. 
         [0003]    2. Description of Related Art 
         [0004]    A large number of vehicles equipped with a keyless entry system incorporating a contact sensing device of an electrostatic capacitance type has appeared on the market. In such a keyless entry system, the contact sensing device is provided at a door handle, and locking and unlocking of the door is controlled according to the contact sensing result. 
         [0005]    As shown in  FIG. 7A , in a standby state of the contact sensing device, a sensing electrode  101  is driven by a drive signal source  102 , and the absence of changes in a capacitance C 101  formed between the sensing electrode  101  and the ground (GND) is detected. Where a user&#39;s finger  103  approaches the sensing electrode  101 , as shown in  FIG. 7B , a capacitance C 102  is formed between the sensing electrode  101  and the finger  103 . Therefore, the contact between the user and the door handle is detected by detecting a change in capacitance corresponding to parallel addition of the capacitance C 102  to the capacitance C 101 . The detection shown in  FIG. 7B  is performed provided that the user carrying an electronic key is present within a detection range determined by the keyless entry system. 
         [0006]    Where the contact sensing device detects the contact with the user who has approached the vehicle from the outside, the vehicle system unlocks the door, and where the contact sensing device detects the contact with the user who steps out of the vehicle, the vehicle system locks the door. 
         [0007]    As described in Japanese Patent Application Publication No. 2010-139362 (JP 2010-139362 A), Japanese Patent Application Publication No. 2009-133777 (JP 2009-133777 A), Japanese Patent Application Publication No. 2007-077797 (JP 2007-077797 A), Japanese Patent Application Publication No. 2012-129762 (JP 2012-129762 A), and Japanese Patent Application Publication No. 2009-218876 (JP 2009-218876 A), the change in electrostatic capacitance caused by rain drops that have adhered to the door handle surface in the rain can be erroneously detected by the aforementioned contact sensing device as the contact with the user. The reason for such erroneous detection caused by rain drops is described below. 
         [0008]      FIG. 8A  is a cross-sectional view taken by cutting a door handle  104  in the vertical direction. The sensing electrode  101  is disposed inside the door handle  104  at a distance from an outer case surface  104   a  of the door handle. The sensing electrode  101  forms a capacitance Ca with the outer case surface  104   a,  and the outer case surface  104   a  forms a capacitance Cb with a body sheet  105  serving as a grounding conductor. Therefore, the capacitance C 101  can be generally represented as a series-combined capacitance of the capacitance Ca and the capacitance Cb. By contrast, as shown in  FIG. 8B , where a rain drop D adheres to the outer case surface  104   a  in the rain, the outer case surface  104   a  and the body sheet  105  form a capacitance Cb′ in a state in which the rain drop is interposed therebetween. 
         [0009]    The state between the sensing electrode  101  and the outer case surface is the same in  FIGS. 8A and 8B , but between the outer case surface and the body sheet  105 , the air is present in  FIG. 8A , whereas the rain drop is present in  FIG. 8B . Since the relative dielectric constant ε r  of air is taken as 1 and the dielectric constant ε r  of water is about 80, the equation C=ε r ε 0 ×S/d representing the capacitance of a parallel flat capacitor (here, ε 0  is the dielectric constant of vacuum, S—the electrode surface area and d—the distance between the electrodes) indicates that the capacitance Cb′ realized when the rain drop has adhered is correspondingly larger than the usual capacitance Cb. Where the contact sensing device detects the change in C (water), which is the value of the capacitance C 101  in  FIG. 8B , with respect to the C (air), which is the value of the capacitance C 101  in  FIG. 8A , at the same level as the change in capacitance caused by the contact with the user&#39;s finger  103 , the contact can be erroneously detected even when there is no contact with the user. 
         [0010]    Accordingly, JP 2010-139362 A suggests using a shift in probability distribution of a capacitance change amount caused by the adhesion of rain drops, and shifting a threshold used for comparing the capacitance change amount for determining the presence/absence of contact during raining. Further, JP 2009-133777 A suggests decreasing the contact detection sensitivity in a location on the door handle where rainwater is likely to remain. JP 2007-077797 A, JP 2012-129762 A, and JP 2009-218876 A also suggest contact sensing devices configured to avoid erroneous detection caused by water. 
         [0011]    However, when a large amount of water covers the vehicle, as in the case where the vehicle is washed in an automatic washing facility or by a high-pressure water jet, with the contact sensing devices of an electrostatic capacitance type of the related art, a state is realized which is close to that when a person touches a door handle and, therefore, the erroneous detection is difficult to avoid. When the vehicle is washed in an automatic washing facility, the user is most often inside the vehicle cabin, but when the vehicle system erroneously detects the water sprayed from the outside of the vehicle cabin as the user&#39;s contact, this is erroneously detected as a state in which an electronic key is left inside the vehicle, and a malfunction of issuing a warning with a hazard lamp or a buzzer can be performed. Further, when the user spray washes the vehicle intensively from the outside of the vehicle, the vehicle system can malfunction and unlock the doors, although the user has no intention to enter the vehicle. The resultant inconvenience for the user is that measures based on his/her own judgment should be taken with respect to such an answerback from the vehicle system. The abovementioned erroneous detection and malfunction can also occur during a storm such as typhoon. 
       SUMMARY OF THE INVENTION 
       [0012]    It is an objective of the invention to provide a contact sensing device of an electrostatic capacitance type that can prevent erroneous detection even when a large amount of water covers a vehicle. 
         [0013]    An aspect of the invention relates to a contact sensing device of an electrostatic capacitance type that detects contact of a human body with a door handle, including: a first electrode and a second electrode disposed inside the door handle and facing each other; a drive detection circuit that drives an electrode connected to a drive detection terminal by the electrostatic capacitance type and detects an electrostatic capacitance change; a first switching circuit that implements switching between connection and disconnection between the first electrode and GND; and a second switching circuit that implements switching between connection and disconnection between the first electrode and the second electrode, wherein the drive detection circuit implements switching between a first state and a second state and detects an electrostatic capacitance change in the first state and an electrostatic capacitance change in the second state. The first state is a state in which the second electrode is connected to the drive detection terminal, the first electrode and the GND are disconnected from each other by the first switching circuit, and the first electrode and the second electrode are connected to each other by the second switching circuit. The second state is a state in which the first electrode and the GND are connected to each other by the first switching circuit and the first electrode and the second electrode are disconnected from each other by the second switching circuit. 
         [0014]    According to the aspect, since the contact sensing device can detect the electrostatic capacitance change caused by the proximity effect of a physical body to the door handle in the first state, the possibility of contact between the human body and the door handle can be detected even when water covering the door handle is present. Further, in the second state, as a result of contact with the door handle, the geometric arrangement of the first electrode and second electrode in the contact sensing device is changed, thereby making it possible to detect the electrostatic capacitance change. The geometric arrangement inside the contact sensing device is unlikely to be changed by a large amount of water, and the detection of changes in the geometrical arrangement caused by unintentional collision with physical bodies can be excluded in conjunction with the result of electrostatic detection in the first state. Therefore, contact with the human body can be accurately identified. It follows from the above that a contact sensing device of a electrostatic capacitance type can be provided such that erroneous detection can be prevented even when the vehicle is covered with a large amount of water. 
         [0015]    Further, the distance between the first electrode and the second electrode may be changed by pressure application to the outer surface of the door handle. 
         [0016]    The geometric arrangement of the first electrode and second electrode inside the contact sensing device can be easily changed by contact between the human body and the door handle. 
         [0017]    The first electrode may have a surface area larger than that of the second electrode. 
         [0018]    Since the electrostatic capacitance formed between the second electrode and the human body by bypassing the first electrode becomes negligibly small, the electrostatic capacitance between the second electrode and the rainwater that has adhered to the door handle because the door handle has been covered with water also becomes negligibly small. Therefore, even when the change of electrostatic capacitance is very small due to a very small change in the inter-electrode distance in the second state, the change in the electrostatic capacitance may be detected with good accuracy. 
         [0019]    Further, a substance having a dielectric constant larger than that of air may be interposed between the first electrode and the second electrode. 
         [0020]    In the second state, the electrostatic capacitance formed between the first electrode and the second electrode can be increased. Therefore, pressure detection sensitivity and detection accuracy can be increased. Further, since the electrostatic capacitance can be increased in a state in which the increase in the electrode surface area is inhibited, the device housing can be reduced in size and good operability can be ensured. 
         [0021]    Further, the detection of the electrostatic capacitance change in the first state and the detection of the electrostatic capacitance change in the second state may be performed alternately a predetermined number of times, and it may be determined that the human body has come into contact with the door handle when changes in the electrostatic capacitance in the first state and the second state are all detected to correspond to the contact of the human body with the door handle over the predetermined number of times. 
         [0022]    Where the human body conies into contact with the door handle, the contact state is maintained for a certain time. Therefore, where a first period and a second period are switched to be repeated a predetermined number of times, the contact with the human body can be continuously determined and erroneous detection caused by noise can be eliminated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
           [0024]      FIG. 1  is a see-through perspective view illustrating an embodiment of the invention and showing the configuration of a contact sensing device; 
           [0025]      FIG. 2  is a see-through perspective view of the vicinity of a door handle that illustrates an embodiment of the invention and explains the arrangement of the contact sensing device; 
           [0026]      FIG. 3  is a circuit diagram illustrating an embodiment of the invention and explaining the first state of the contact sensing device; 
           [0027]      FIG. 4  is a circuit diagram illustrating an embodiment of the invention and explaining the first state of the contact sensing device; 
           [0028]      FIG. 5  illustrates an embodiment of the invention and explains the operation sequence of the contact sensing device; 
           [0029]      FIG. 6  is a flowchart illustrating an embodiment of the invention and explaining the operation of the contact sensing device; 
           [0030]      FIG. 7A  is a circuit diagram in a standby state that illustrates the related art; 
           [0031]      FIG. 7B  is a circuit diagram in a state of contact with a human body that illustrates the related art; 
           [0032]      FIG. 8A  illustrates the related art and explains a state in which the door handle is not covered with water; and 
           [0033]      FIG. 8B  illustrates the related art and explains a state in which the door handle is covered with water. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0034]    An embodiment of the invention is explained below with reference to the appended drawings. 
         [0035]      FIG. 2  is a general view of the configuration of a door handle  10  according to the embodiment. In this case, the attention is focused on the arrangement of a contact sensing device  1  in the door handle  10 . 
         [0036]    The door handle  10  is shown as a door handle of a driver door. The contact sensing device  1  is a device of an electrostatic capacitance type, and a region (see  FIG. 1 ) to be contacted by the user&#39;s finger is set at the upper surface close to the front end of the door handle  10 . The contact sensing device  1  is provided with an electrode  1   a,  an electrode  1   b,  and a drive detection circuit  1   c.  The electrode In is provided at a position which is set inward of the door handle  10  from an outer case surface  10   a,  so as to face the abovementioned region. Other members of the contact sensing device  1  are disposed inside the door handle  10  with reference to the position of the electrode  1   a.  Thus, the electrode  1   b  is disposed below the electrode  1   a  and opposite thereto, and the drive detection circuit  1   c  is provided at a circumferential location on the side or below the electrode  1   a  and the electrode  1   b.    
         [0037]      FIG. 1  shows the detailed configuration of the contact sensing device  1 . For the convenience of illustration, the door handle  10  is appropriately cut, only the circumference where the contact sensing device  1  is provided is taken out, and the members of the contact sensing device  1  are shown by solid lines in a state in which the interior of the door handle  10  is seen through. 
         [0038]    The region to be contacted by a user&#39;s finger (human body)  20  in the door handle  10  is provided to be visible as a pad region  10   x.  The electrode (first electrode) la is mounted on the inner surface of a resin body with a thickness δ that constitutes a case  10 A, so that the resin body is interposed between the electrode and the outer case surface  10   a  of the door handle  10 . Thus, a distance equal to δ is maintained between a site P on the pad region  10   x,  which is contacted by the finger  20 , and the electrode  1   a.  The electrode  1   a  is formed to have a surface area larger than that of the electrode  1   b,  and the electrode (second electrode)  1   b  is fixed so as to be accommodated in a region directly below the electrode  1   a  and arranged opposite thereto. 
         [0039]    In  FIG. 1 , the interior of the case  10 A surrounded by the resin body is shown as an empty space, but a dielectric having a dielectric constant (relative dielectric constant) larger than that of air, in particular, a substance with a high dielectric constant, such as an urea resin or Rochelle salt, may be interposed between the electrode  1   a  and the electrode  1   b.  The distance between the electrode  1   a  and the electrode  1   b  is changed when the outer case surface  10   a  is pushed by the finger  20  and the case  10 A is deformed. 
         [0040]    The drive detection circuit  1   c  performs a drive detection operation by an electrostatic capacitance method such as a switched capacitor method. In  FIG. 1  this circuit is shown as a block outlining the circuit, and the shape and arrangement thereof are not specified. Since a conventional circuit can be used for, such drive detection operation, it is not explained herein in detail. The drive detection circuit  1   c  can be controlled, for example, by a door lock sensor and a door lock electronic control unit (ECU). The drive detection circuit  1   c  drives, by the abovementioned electrostatic capacitance method, at least either of the electrodes connected to a drive detection terminal O, as described hereinbelow, from among the electrode  1   a  and the electrode  1   b.  The change of the connected electrostatic capacitance is detected through the drive detection terminal O. The other terminal of the electrostatic capacitance that forms a pair with the drive detection terminal O, which is the one terminal, is a reference potential terminal such as GND (this terminal is not shown in the figure). 
         [0041]    The electrode  1   b  is connected at all times to the drive detection terminal O. The contact sensing device  1  is provided with a switching circuit (first switching circuit) SW 1  and a switching circuit (second switching circuit) SW 2  that switch the connection state of the electrode  1   a  with the drive detection terminal O and the electrode  1   b.  The switching circuit SW 1  switches connection/disconnection between the electrode  1   a  and the OND. The switching circuit SW 2  switches connection/disconnection between the electrode  1   a  and the electrode  1   b,  that is, the drive detection terminal O. The switching circuit SW 1  and the switching circuit SW 2  are controlled by a complementary logic such that the connection state and disconnection state are alternately reversed, for example, by the same control signal cs outputted from the drive detection circuit  1   c.  Examples of such switching circuit SW 1  and switching circuit SW 2  include an n-channel field effect transistor and a p-channel field effect transistor, and also a pnp bipolar transistor and an npn bipolar transistor. The switching circuit SW 1  and the switching circuit SW 2  may be also controlled by respective independent control signals. In this case, transistors of the same polarity can be used as the switching circuit SW 1  and the switching circuit SW 2 . The drive detection circuit  1   c  continues the operation of periodically switching the connection state with the switching circuit SW 1  and the connection state with the switching circuit SW 2  in a standby state and also in a state of contact with the user. 
         [0042]    The electrode  1   a  in the abovementioned example is provided such as to face the upper surface of the door handle  10 , but this electrode may be also provided so as to face other location, for example, a side surface  10   m  of the door handle  10  which is farther from the door panel  11 , as shown in  FIG. 2 . Further, the electrode  1   a  in the abovementioned example is explained without distinguishing between the applications for locking and unlocking the door, but it is also possible to provide separately an electrode In on the side surface of the door handle  10  on the door panel  11  side, and use the electrode  1   a  as a sensing electrode for locking and use the electrode  1   n  as a sensing electrode for unlocking as shown in  FIG. 2 . The electrode  1   n  is also combined with one more electrode forming a pair therewith, in the same manner as with the electrode  1   b.    
         [0043]    The operation of the contact sensing device  1  of the above-described configuration is explained below with reference to  FIGS. 3 to 6 . Considered below is a state when the user&#39;s finger  20  touches the pad region  10   x  after the electronic key has been recognized by the vehicle system. 
         [0044]    A state in which the electrode  1   a  and the GND are disconnected from each other by the switching circuit SW 1 , and the electrode  1   a  and the electrode  1   b  are connected to each other by the switching circuit SW 2 , as shown in  FIG. 3 , is referred to as the first state. In the first state, the electrostatic capacitance C 1  is formed between the finger  20  and the electrode  1   a  connected to the electrode  1   b.  The drive detection circuit  1   c  performs the operation of applying a drive voltage to the electrostatic capacitance C 1  connected to the drive detection terminal O and determining, by comparison with the first time threshold, the duration of time till a reference voltage is reached inside the drive detection circuit  1   c.  Where a change amount of electrostatic capacitance exceeding a threshold (first threshold corresponding to the first time threshold) is detected by comparing with the electrostatic capacitance that has been formed between the GND (body sheet) and the electrode  1   a  connected to the electrode  1   b  before the finger  20  touches the pad region  10   x,  it is determined that the user could touch the door handle  10 . Such change amount of electrostatic capacitance that exceeds the threshold can be also detected when the vehicle is covered with water. 
         [0045]    A state in which the electrode  1   a  and the GND are connected to each other by the switching circuit SW 1 , and the electrode  1   a  and the electrode  1   b  are disconnected from each other by the switching circuit SW 2 , as shown in  FIG. 4 , is referred to as the second state. In the second state, the electrostatic capacitance C 2  is formed between the electrode  1   a  and the electrode  1   b.  In this state, in the same manner as in the first state, when the finger  20  is pressed against the pad region  10   x,  the case  10 A is deformed, the electrode  1   a  displaces downward, and the distance (inter-electrode distance) between the electrode  1   a  and the electrode  1   b  decreases from d 0  before the pressure was applied by the finger  20  to d 1  (d 1 &lt;d 0 ). As a result, as follows from the equation above that represents the capacitance of the parallel flat capacitor, the electrostatic capacitance C 2  becomes larger than the value in the standby state. Further, since the electrode  1   a  is connected to the GND, the effective electrostatic capacitance C 3  is not formed between the electrode  1   a  and the GND (body sheet). Further, the electrode  1   b  can form the electrostatic capacitance with the finger  20  by bypassing the circumference of the electrode  1   a,  but since the surface area of the electrode  1   a  is increased over that of the electrode  1   b,  the electrostatic capacitance formed between the electrode  1   b  and the finger  20  is negligibly small. In particular, where the electrode  1   b  is accommodated in the region directly below the electrode  1   a,  the electrostatic capacitance formed between the electrode  1   b  and the finger  20  can be made even smaller. 
         [0046]    The drive detection circuit  1   c  performs the operation of applying a drive voltage to the electrostatic capacitance C 2  connected to the drive detection terminal O and determining, by comparison with the second time threshold, the duration of time till a reference voltage is reached inside the drive detection circuit  1   c.  Where a change amount of electrostatic capacitance exceeding a threshold (second threshold corresponding to the second time threshold) is detected by comparing with the electrostatic capacitance C 2  formed when the inter-electrode distance is d 0 , it is determined that the user has touched the door handle  10 . The change amount of electrostatic capacitance that exceeds the threshold is such that cannot be caused by the application of water pressure to the vehicle when the vehicle is covered with a large amount of water as a result of setting the rigidity of the case  10 A. Since the electrostatic capacitance formed between the electrode  1   b  and the finger  20  is reduced as mentioned hereinabove, the electrostatic capacitance between the electrode  1   b  and the rainwater, which is caused by the water covering the door handle  10 , is also reduced to a negligibly small level. Therefore, in the second state, even though the change in the electrostatic capacitance C 2  is very small due to a very small change in the inter-electrode distance, the change in the electrostatic capacitance C 2  can be detected with good accuracy. 
         [0047]    Further, as described hereinabove, the electrostatic capacitance C 2  can be increased by interposing a dielectric with a relative dielectric constant greater than 1, primarily a substance with a high dielectric constant, between the electrode  1   a  and the electrode  1   b.  Therefore, pressure detection sensitivity and detection accuracy can be increased. As a result, the electrostatic capacitance C 2  can be increased in a state in in which the increase in electrode surface area is inhibited. Therefore, the device housing can be reduced in size and good operability can be ensured. Another effect that can be obtained with the configuration in which a dielectric is inserted between the electrode  1   a  and the electrode  1   b  is that the electrodes can be fixed in a state in which a pressure-induced displacement is allowed. 
         [0048]    Thus, in the embodiment, the contact sensing device  1  is initially set into the first state and it is detected whether or not the electrostatic. capacitance C 1  has changed from the standby state to exceed the first threshold. Then, the contact sensing device  1  is set into the second state and it is detected whether or not the electrostatic capacitance C 2  has changed from the standby state to, exceed the second threshold. Where the capacitance change that exceeds both the first threshold and the second threshold is detected, it is determined that the user has come into contact with the door handle  10 . The capacitance change in the first state is determined by the proximity effect of the physical body to the door handle  10 , and the capacitance change in the second state is determined by the change of the geometric arrangement of the electrode  1   a  and the electrode  1   b  inside the contact sensing device  1  corresponding to the pressure applied to the door handle  10 . 
         [0049]    The geometric arrangement inside the contact sensing device  1  is unlikely to be changed by a large amount of water, and the detection of changes in the geometrical arrangement caused by unintentional collision with physical bodies can be excluded in conjunction with the result of electrostatic, detection in the first state. Therefore, contact with the human body can be accurately identified. It follows from the above that a contact sensing device of an electrostatic capacitance type can be provided such that erroneous detection can be prevented even when the vehicle is covered with a large amount of water. Further, the effect of making the geometric arrangement unlikely to change when the vehicle is covered with water is particularly significant when the position of the electrode  1   a  explained in  FIG. 2  faces the upper surface of the door handle  10 . 
         [0050]    Further, the determination operation in the first state and the second state can be performed by the drive detection circuit  1   c,  but it can be also implemented in the control circuit such as the door lock ECU controlling the drive detection circuit  1   c  by performing, as necessary, the analog-to-digital (AD) conversion from the detection result outputted from the drive detection circuit  1   c.    
         [0051]    Further, the door handle corresponding to the keyless entry system such as shown in  FIG. 2  is configured of an outer portion (case  10 A) constituting a design surface and an inner assembly of the detection circuit and sensor electrodes (electrode  1   a,  electrode  1   b,  drive detection circuit  1   c,  etc.). The products in which the, sensor electrode shape is changed for each design should have been conventionally prepared as the inner assemblies, but with the door handle  10  of the embodiment, an inner assembly of one type can be shared by all designs since the electrode (electrode  1   a ) on the side close to the operation portion is molded integrally with the outer portion. 
         [0052]    The sequence of the abovementioned capacitance sensing operation, contact detection operation, and door locking-unlocking control is explained below. 
         [0053]    As shown in  FIG. 5 , the execution of the capacitance sensing operation and contact detection operation is switched such that a first period T 1  relating to the first state in which the capacitance formed with the human body is detected and a second period T 2  relating to the second state in which the pressure applied to the door handle  10  is detected are repeated a plurality of times. In other words, in each first period T 1 , the contact sensing device  1  is set to the first state, the capacitance variation amount induced by the electrostatic capacitance C 1  is detected, and the possibility of the user coming into contact with the door handle  10  is determined. In each second period T 2 , the contact sensing device  1  is set to the second state, the capacitance variation amount induced by the electrostatic capacitance C 2  is detected, and whether or not the user has come into contact with the door handle  10  is determined. Where the user comes into contact with the door handle  10 , the contact state is maintained for a certain time. Therefore, where the first period T 1  and the second period T 2  are repeated a predetermined number of times at an interval of several milliseconds, the contact with the user can be continuously determined and the erroneous detection caused by noise can be eliminated. The length of each period is the same as the response time in a contact sensing device of the related art. Therefore, the detection processing circuit of the related art can be used for detecting the capacitance change amount. A reset period Tr for returning the electric charges of the electrode  1   a  and the electrode  1   b  to the initial state is provided between the first period T 1  and the second period T 2 . 
         [0054]      FIG. 6  shows a flowchart explaining the operation of the contact sensing device  1  incorporating the sequence shown in  FIG. 5 . Steps S 101  to S 106  described hereinbelow may be executed to completion in the contact sensing device  1 , or any of the steps may be executed by a control circuit such as the door lock ECU. The control may be executed by hardware alone, or with a computer configuration in which a processor reads a program describing the operations of those steps from the memory and executes the program. Where the control circuit relates to control, the control circuit is included in a member constituting the contact sensing device  1 . 
         [0055]    In the state considered hereinbelow, the contact sensing device  1  executes the sequence shown in  FIG. 5  at all times, regardless of whether an ignition power source is ON or OFF. In step S 101 , an initial value of 0 is introduced as the number N of contacts of the user with the door handle  10  that is determined through a pair of periods constituted by the first period T 1  and the very next second period T 2 . In step S 102 , the detection (first detection) in the first period T 1  is performed, and then in step S 103 , the detection in the second period T 2  (second detection) is performed. 
         [0056]    In step S 104 , it is determined whether or not the capacitance change amount (first capacitance change amount) caused by the formation of the electrostatic capacitance C 1  exceeds the first threshold on the basis of the result of detection in step S 102 , and it is also determined whether or not the capacitance change amount (second capacitance change amount) of the electrostatic capacitance C 2  exceeds the second threshold on the basis of the result of detection in step S 103 . Where it is determined in step S 104  that the first capacitance change amount exceeds the first threshold and the second capacitance change amount exceeds the second threshold, the processing advances to step S 105 , and where the first capacitance change amount does not exceed the first threshold or the second capacitance change amount does not exceed the second threshold, the processing returns to step S 101 . 
         [0057]    In step S 105 , N is incremented by 1. Then, in step S 106 , it is determined whether or not N has reached a specified number k corresponding to the predetermined number of times. Where N has reached k, it is finally determined that the user has come into contact with the door handle  10 , and the processing advances to step S 107 . Where N has not reached k, the processing returns to step S 102 . 
         [0058]    In step S 107 , the determination that the user has come into contact with the door handle  10  is received, and the door lock ECU performs a door lock output. Thus, the door lock ECU locks the door in a situation corresponding to door locking and unlocks the door in a situation corresponding to door unlocking. The series of control operations from the user contact detection to the door locking or unlocking is thereby ended. 
         [0059]    In the operation sequences shown in  FIGS. 5 and 6 , the order of the first period T 1  and the second period T 2  may be reversed. 
         [0060]    Where the contact sensing device  1  executes the sequence shown in  FIGS. 5 and 6  at all times, regardless of ON/OFF of the vehicle power supply, as in the above-described example, the contact sensing device  1  performs the operation even when a user who is unaware that the vehicle power source is not switched off, as can happen in a vehicle with a low operation noise when the vehicle power source is ON, such as a hybrid vehicle, locks or unlocks the door. Therefore, adequate contact detection can be performed at all times. Further, with the object of reducing power consumption, the operation power may be also supplied to the contact sensing device  1  only when necessary, 
         [0061]    The invention can be generally used in vehicles equipped with a security function.