Patent Publication Number: US-9904363-B2

Title: Input apparatus for generating tactile sensations and control method of input apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Japanese Patent Application No. 2008-326297 filed on Dec. 22, 2008, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to input apparatuses having input units for receiving pressure inputs. 
     BACKGROUND ART 
     In recent years, input apparatuses having input units in the form of a plate for receiving inputs by pressure such as touch panels, touch switches and the like are popularly used as input units for receiving input operations by the user in information equipments, home electric appliances and the like. Such input units have a variety of types, such as resistive film type, capacitive type and the like. All of these input units are for receiving pressure inputs by fingers and stylus pens and, unlike push-button switches, they are not displaced even when being pressed. 
     Therefore, an operator cannot obtain feedback when the pressure input is received by the input unit. As a result, when using the input apparatus having the touch panel, for example, the operator is likely to input erroneously by tapping multiple times on the same spot, which may be stressful for the operator. 
     As methods to prevent such erroneous inputs, there are known methods for visually or auditory confirming the input operations by, for example, generating sounds or by changing a display state, such as colors of input objects such as input buttons and the like graphically displayed on a display unit, correspondingly to a pressured area upon reception of the pressure inputs. 
     However, such auditory feedback may be difficult to be confirmed in a noisy environment and is not applicable when the equipment being used is in a silent mode. In addition, in using such visual feedback, if the input object displayed on the display unit is small, the operator may not be able to confirm the change in the display state, and particularly when the operator is inputting by a finger, a view of the input object is blocked by the finger. 
     There is also suggested a feedback method relying on neither the auditory nor visual sensation but instead generating a tactile sensation at operator&#39;s fingertip by vibrating the touch panel upon reception of an input thereon (for example, see Patent Documents 1, 2). 
     RELATED ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Patent Laid-Open No. 2003-288158 
     Patent Document 2: Japanese Patent Laid-Open No. 2008-130055 
     SUMMARY OF INVENTION 
     Technical Problem 
     The techniques disclosed in the above Patent Documents 1 and 2, however, merely generate the tactile sensation by vibration at the operator&#39;s fingertip. That is, they provide a mere “throbbing” sensation at the operator&#39;s fingertip touching the touch panel by vibrating the touch panel and not a realistic click sensation such as “click” which is obtained when operating, for example, a push-button switch with a metal dome. 
     Therefore, the operator may have a feeling of strangeness if the above feedback techniques are applied to the touch panels of, for example, input keys of the information equipments such as mobile terminals of mobile phones, calculators, ticket vending machines and the like and input keys of operation units of the home electric appliances such as microwaves, TV sets and the like. 
     In addition, in order to provide suitable feedback to the fingertip of the operator, there is considered an apparatus which has a load threshold set and vibrates the touch panel not only when a pressure load detected when the touch panel is pressed by a finger increases and reaches the load threshold but also when a pressure load detected when the finger is released from the touch panel decreases and reaches the load threshold. Being capable of vibrating the touch panel corresponding respectively to a pressing operation and a releasing operation by the operator, this apparatus can provide a suitable operational feeling to the operator. However, if the pressure load when the touch panel is pressed does not exceed the load threshold but is only detected up to a value equal to the load threshold, the touch panel is vibrated only in pressing and not in releasing, causing the operator the feeling of strangeness. Especially when a continuous input operation is performed to the same input object on the touch panel, the touch panel may vibrate only in pressing to an input operation while vibrating both in pressing and in releasing to another input operation, giving the operator a significant feeling of strangeness. 
     Accordingly, an object of the present invention in consideration of such conditions is to provide an input apparatus capable of providing the realistic click sensation, similar to that obtained when the push-button switch is operated, and enables the operator to perform continuous input operation (repetitive tap) without feeling of strangeness, when an operator operates the input unit of a pressure type. 
     Solution to Problem 
     In order to achieve the above object, an input apparatus according to a first aspect of the present invention includes: 
     an input unit for receiving a pressure input; 
     a load detection unit for detecting a pressure load on the input unit; 
     a vibration unit for vibrating the input unit; and 
     a control unit for controlling drive of the vibration unit such that a first tactile sensation is provided to an object pressing the input unit, when the pressure load detected by the load detection unit satisfies a predetermined standard for receiving an input to the input unit, and for controlling drive of the vibration unit such that a second tactile sensation is provided to the object, when the pressure load detected by the load detection unit satisfies a standard lower than the predetermined standard for receiving the input to the input unit after the input to the input unit is received, wherein the second tactile sensation is the same as the first tactile sensation. 
     In addition, in order to achieve the above object, an input apparatus according to a second aspect of the present invention includes: 
     an input unit for receiving a pressure input; 
     a load detection unit for detecting a pressure load on the input unit; 
     a vibration unit for vibrating the input unit; and 
     a control unit for controlling drive of the vibration unit such that a first tactile sensation is provided to an object pressing the input unit, when the pressure load detected by the load detection unit satisfies a predetermined standard for receiving an input to the input unit, and for controlling drive of the vibration unit such that a second tactile sensation is provided to the object, when the pressure load detected by the load detection unit satisfies a standard lower than the predetermined standard for receiving the input to the input unit after the input to the input unit is received, wherein the second tactile sensation is different from the first tactile sensation. 
     Moreover, in order to achieve the above object, a control method of an input apparatus according to a third aspect of the present invention is a control method of an input apparatus including an input unit for receiving a pressure input, and a load detection unit for detecting a pressure load on the input unit and a vibration unit for vibrating the input unit, and includes the step of: 
     controlling drive of the vibration unit such that a first tactile sensation is provided to an object pressing the input unit, when the pressure load detected by the load detection unit satisfies a predetermined standard for receiving an input to the input unit, and controlling drive of the vibration unit such that a second tactile sensation is provided to the object, when the pressure load detected by the load detection unit satisfies a standard lower than the predetermined standard for receiving the input to the input unit after the input to the input unit is received, wherein the second tactile sensation is the same as the first tactile sensation. 
     Moreover, in order to achieve the above object, a control method of an input apparatus according to a third aspect of the present invention is a control method of an input apparatus including an input unit for receiving a pressure input, a load detection unit for detecting a pressure load on the input unit and a vibration unit for vibrating the input unit, and includes the step of: 
     controlling drive of the vibration unit such that a first tactile sensation is provided to an object pressing the input unit, when the pressure load detected by the load detection unit satisfies a predetermined standard for receiving an input to the input unit, and controlling drive of the vibration unit such that a second tactile sensation is provided to the object, when the pressure load detected by the load detection unit satisfies a standard lower than the predetermined standard for receiving the input to the input unit after the input to the input unit is received, wherein the second tactile sensation is different from the first tactile sensation. 
     Effect of the Invention 
     According to the present invention, the input unit vibrates when the pressure load on the input unit satisfies a predetermined standard for receiving the input and then the input unit vibrates when the pressure load on the input unit satisfies a standard lower than the predetermined standard for receiving the input. Thereby, it provides the operator with a realistic click sensation the same as that obtained when operating a push-button switch, allowing the operator to perform a continuous input operation (repetitive tap) without having a feeling of strangeness. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a general load characteristic of a push-button switch; 
         FIG. 2  is a diagram illustrating results of sensory evaluations on operations of a variety of push-button switches with different pressure loads; 
         FIG. 3  is a diagram illustrating results of sensory evaluations on operations of a variety of push-button switches with different strokes; 
         FIG. 4  is a diagram illustrating an exemplary result of a measurement of a vibration generated at a push button upon operation of the push-button switch; 
         FIG. 5  is a block diagram illustrating a schematic constitution of an input apparatus according to a first embodiment of the present invention; 
         FIG. 6  shows an exemplary housing structure of the input apparatus shown in  FIG. 5 ; 
         FIG. 7  is a flowchart of operations by the input apparatus shown in  FIG. 5 ; 
         FIG. 8  is a diagram illustrating an example of click sensation provided by the input apparatus shown in  FIG. 5  when a standard load of pressing and that of releasing are set to be equal; 
         FIG. 9  is a diagram illustrating an example of click sensation provided by the input apparatus shown in  FIG. 5  when the standard load of releasing is set to be less than that of pressing; 
         FIG. 10  is a block diagram illustrating a schematic constitution of an input apparatus according to a second embodiment of the present invention; 
         FIG. 11  is a front view of the input apparatus shown in  FIG. 10 ; 
         FIG. 12  is a diagram illustrating results of sensory evaluations on a click sensation when varying the frequency of a drive signal to drive the vibration unit shown in  FIG. 5 ; 
         FIG. 13  is a diagram illustrating results of sensory evaluations on the click sensation when varying the vibration amplitude of a touch panel shown in  FIG. 5 ; 
         FIG. 14  is a diagram illustrating results of sensory evaluations on the click sensation when varying the period of the drive signal to drive the vibration unit shown in  FIG. 5 ; 
         FIG. 15  is a diagram illustrating results of sensory evaluations on the click sensation when varying the waveform of the drive signal to drive the vibration unit shown in  FIG. 5 ; 
         FIG. 16  is a diagram illustrating the waveform of the drive signal to drive the vibration unit and an actual waveform of the vibration amplitude on the touch panel; 
         FIG. 17  is a diagram illustrating an exemplary result of sensory evaluations on the click sensation by the input apparatus shown in  FIG. 5  comparing with and without a release tactile sensation; 
         FIG. 18  is a diagram illustrating an example of sensation provided upon continuous input when the standard load of pressing and that of releasing are set to be equal; 
         FIG. 19  is a diagram illustrating an example of sensation provided upon continuous input when the standard load of releasing is set to be too low relative to that of pressing; 
         FIG. 20  is a diagram illustrating an example of sensation provided upon continuous input when the standard load of releasing is set close to that of pressing; 
         FIG. 21  is a diagram illustrating exemplary results of sensory evaluations on sensation provided when the standard load of pressing is set at 1 N; 
         FIG. 22  is a diagram illustrating exemplary results of sensory evaluations on sensation provided when the standard load of pressing is set at 2 N; and 
         FIG. 23  is a diagram illustrating exemplary results of sensory evaluations on sensation provided when the standard load of pressing is set at 3 N. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Prior to descriptions of embodiments of the present invention, a description of a principle of a method to provide a click sensation by an input apparatus according to the present invention is presented. 
     For tactile sensory awareness, a human has a nerve responsible for a pressure sensation to feel the touch such as hardness or softness of an object from a load introduced to a bone and a muscle when touching the object, and another nerve responsible for a tactile sensation to feel a texture of the object and the like by detecting a vibration introduced to a skin surface when touching the object. That is, the pressure sensation detects the load, whereas the tactile sensation detects the vibration. In addition, a tactile sensation is generally a combination of the pressure sensation and the tactile sensation. Accordingly, reproduction of a stimulus, similar to the stimulus to the “pressure sensation” and the “tactile sensation” when operating a push-button switch, on a touch panel enables to provide a click sensation to an operator. 
     On the other hand, metal dome switches, emboss switches, rubber switches, tactile switches and the like, for example, are widely known as the push-button switches used for information equipments and home electric appliances. Although there are differences in the stroke of a push button and the applied load (pressing force) according to types of the switches, those general push-button switches basically have load characteristics as shown in  FIG. 1 . 
     In the load characteristics in pressing in  FIG. 1 , a period from a point A to a point B represents a period in which a load increases in substantially proportion to pressing down from a start of pressing the push button. A period from the point B to a point C represents a period in which a convex elastic member such as the metal dome is buckled since the push button is pressed down, and thus the load is rapidly decreased. A period from the point C to a point D represents a period in which a contact point of the switch is closed and the load increases in substantially proportion to pressing down. 
     Although there is a hysteresis to some degrees, the load characteristics of the push button in releasing retrace a change of the load in pressing. That is, a period from the point D to a point E represents a period in which the load decreases in substantially promotion to release from a start thereof and the contact point of the switch maintains a closed state. A period from the point E to a point F represents a period in which the elastic member recovers in a convex form from a buckled form by release of the push button and the load increases rapidly, and at start of this period the contact point of the switch is open. A period from the point F to a point G represents a period in which a finger is released from the push button after recovery of the elastic member and the load decreases in substantially proportion to the release. 
     In the load characteristics shown in  FIG. 1 , a maximum stroke of the push button is minimal; equal to or less than 1 mm for the metal dome switch, the emboss switch and the tactile switch, and equal to or less than 3 mm for the rubber switch, for example. In addition, loads at the point B are around 1 N to 6 N, for example, on the metal dome switch, the emboss switch and the tactile switch and around 0.5 N, for example, on the rubber switch. The operator can feel the click sensation when operating any of those push-button switches. 
     As such, inventors of the present invention studied what kind of movement of the push-button switch provides the click sensation created by the “pressure sensation” and the “tactile sensation”. First, it is studied which causes the click sensation, change in the stroke or change in the pressure load. 
       FIG. 2  is a diagram illustrating results of sensory evaluations on how the operator felt when operating a variety of push-button switches with different pressure loads. A horizontal axis represents an actual pressure load and a vertical axis represents how operators felt about the push-button switches, heavy or light, on a scale of 1 to 7. Subjects as the operators were five people who were accustomed to use of mobile terminals. As can be seen in  FIG. 2 , it is shown that they could percept that push-button switches with high pressure loads were heavy and others with low pressure loads were light. 
       FIG. 3  is a diagram illustrating results of sensory evaluations on how the operators felt when operating a variety of push-button switches with different strokes. A horizontal axis represents actual strokes and a vertical axis represents how the operators felt about the push-button switches, long or short, on a scale of 1 to 7. Subjects as the operators were five people, the same as those in  FIG. 2 , who were accustomed to use of mobile terminals. As can be seen in  FIG. 3 , they cannot clearly percept whether a minimal stroke is long or short. 
     The results of sensory evaluations presented above shows that the human can percept a difference in the load but not a difference in the minimal stroke. 
     Therefore, the inventors focused on a change in the pressure load. That is, since the human cannot percept the difference in the stroke, it was studied whether the human can feel the click sensation if the pressure load on a plane such as a touch panel, that is, a stimulus to the pressure sensation is changed following the points A, B and C in  FIG. 1 . Therefore, an experimental apparatus having a plate displaceable in a vertical direction was prepared. Then, the plate was pressed down from the point A to the point B as shown in  FIG. 1 , and at a point when a load reached the load at the point B the plate was instantaneously displaced downward slightly in order to reproduce the change in the load between the points B, C. 
     As a result, although a “sense of pressing” to “have pressed down” the push-button switch was obtained, the realistic click sensation such as “click” which could be obtained when operating the metal dome switch, for example, was not obtained. That is, it was found out that there is another element, which cannot be cleared by a relationship between the stroke and the load, in order to obtain the realistic click sensation. 
     As such, the inventors next studied focusing not only on the “pressure sensation” but also the “tactile sensation”, which is another sensibility. Accordingly, with a variety of mobile terminals having the input apparatus with the push-button switches of the metal dome switches mounted thereon, the inventors measured vibrations generated at push buttons when the push buttons were operated. As a result, it was found out that at a point when the pressure load reached the point B in  FIG. 1 , that is, at a point when the metal dome started being buckled, the push button vibrated at a frequency of approximately 100-200 Hz. 
       FIG. 4  is a diagram illustrating an exemplary result of such measurement. A horizontal axis represents a pressure elapsed time, whereas a vertical axis represents vibration amplitude. This push-button switch vibrates as shown by a solid line in  FIG. 4  at the point B in  FIG. 1 . Thereby, it was found out that the human receives 1 period of vibration stimulus of about 6 ms (a frequency of approximately 170 Hz) when pressing this push-button switch. In addition, at a point when the pressure load on the push-button switch reached the point F in  FIG. 1  in releasing, that is, at a point when the metal dome recovered from the buckled state, this push button vibrated as shown by the dashed line in  FIG. 4 . Thereby, it was found out that in case of this push-button switch the human receives 1 period of the vibration stimulus of about 8 ms (a frequency of approximately 125 Hz) at release. 
     The above results show that it is possible to provide the operator with the click sensation similar to that obtained when operating the push-button switch having the result of measurement as shown in  FIG. 4 , when the operator presses down the input unit of a pressure type in the form of a plate such as the touch panel, if the input apparatus stimulates the pressure sensation by letting the operator voluntarily press down the input unit without vibration when the load is from the point A to the point B shown in  FIG. 1  and, at the point B, stimulates the tactile sensation by vibrating the input unit for 1 period at the frequency of 170 Hz. 
     Based on the above principle, when the input unit of the pressure type in the form of the plate is pressed down, the input apparatus according to the present invention stimulates the pressure sensation until the pressure load satisfies a predetermined standard for receiving an input to the input unit and, when the standard is satisfied, stimulates the tactile sensation by vibrating the input unit with a predetermined drive signal, that is, with a frequency, period which means drive time (wavelength), waveform and vibration amplitude. 
     In addition, when operating the push-button switch, the human receives a tactile stimulus as shown in  FIG. 4  at a finger from the push-button switch not only in pressing but also in releasing. As such, the input apparatus according to the present invention provides the operator with the click sensation in releasing as well (hereinafter, the click sensation in releasing is also referred to as a release tactile sensation, arbitrarily). Thereby, the input apparatus provides the operator with a more realistic click sensation similar to that obtained upon pressing the push-button switch down. 
     Moreover, according to the present invention, for the input apparatus employed in the mobile terminals, a standard for providing the release tactile sensation corresponding to a standard for providing the click sensation in pressing is set appropriately, in order to provide the operator with the realistic click sensation without a feeling of strangeness for a so-called repetitive tap, in which the same input object is continuously inputted, often performed to input telephone numbers, messages and the like. 
     Embodiments of the present invention will be described with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 5  is a block diagram illustrating a schematic constitution of an input apparatus according to a first embodiment of the present invention. This input apparatus has a display panel  11 , a touch panel  12 , a load detection unit  13 , a vibration unit  14 , and a control unit  15  for controlling overall operations. The display panel  11  constitutes a display unit for displaying input objects such as an input button and the like and may be, for example, a liquid crystal display panel, an organic EL display panel or the like. The touch panel  12  constitutes the input unit for receiving a pressure input to the display panel  11  and may be of a known type such as, for example, a resistive film type, a capacitive type or the like. The load detection unit  13  detects a pressure load on the touch panel  12  and may include, for example, a strain gauge sensor. The vibration unit  14  vibrates the touch panel  12  and may include, for example, a piezoelectric vibrator. 
       FIG. 6  shows an exemplary housing structure of the input apparatus shown in  FIG. 5 ;  FIG. 6( a )  is a cross-sectional view of a main section and  FIG. 6( b )  is a plane view of the main section. The display panel  11  is contained in a housing  21 . A touch panel  12  is disposed on the display panel  11  via insulators  22  made of elastic members. In the input apparatus according to the present embodiment, the display panel  11  and the touch panel  12  are rectangular in shape in a planer view and the touch panel  12  is disposed on the display panel  11  via the insulators  22 , which are arranged outside a display area A of the display panel  11  shown by a chain double-dashed line in  FIG. 6( b ) . 
     In addition, the housing  21  is provided with an upper cover  23  covering a surface area of the touch panel  12  outside the display area of the display panel  11 . Insulators  24  made of elastic members are arranged between the upper cover  23  and the touch panel  12 . 
     The touch panel  12  may have a surface, that is, an operation plane constituted by a transparent film and a rear face constituted by a glass plate and may be designed such that the transparent film of the surface is bent (strained) slightly in accordance with the pressure when the operation plane is pressed. 
     A strain gauge sensor  31  for detecting a load (pressuring force) applied on the touch panel  20  is provided, adhered or the like, on the transparent film of the surface of the touch panel  12  at a position close to each side covered by the upper cover  23 . In addition, a piezoelectric vibrator  32  for vibrating the touch panel  12  is provided, adhered or the like, on the glass plate of the rear face of the touch panel  12  close to an edge of each of two opposed sides. That is, the input apparatus shown in  FIG. 6  has the load detection unit  13  in  FIG. 5  including four strain gauge sensors  31  and the vibration unit  14  including two piezoelectric vibrators  32 . It is to be noted that the housing  21 , the upper cover  23  and the insulator  24  shown in  FIG. 6( a )  are omitted in  FIG. 6( b ) . 
       FIG. 7  is a flowchart of operations by the input apparatus according to the present invention. The control unit  15  monitors an input to the touch panel  12  as well as a load detected by the load detection unit  13 . The control unit  15  detects that the input to the touch panel  12  is an input to the input object displayed on the display panel  11 , and that the pressure load detected by the load detection unit  13  increases with pressure on the touch panel  12  and reaches a predetermined standard for receiving the input (step S 81 ). Upon detecting that, the control unit  15  receives the input to the touch panel  12  at a point of detection and drives the vibration unit  14  with a predetermined drive signal to vibrate the touch panel  12  in a predetermined vibration pattern (step S 82 ). Thereby, the click sensation is provided to the operator via a finger or an object such as a stylus pen which is pressing the touch panel  12 , such that the operator recognizes that an input operation is completed. The load detection unit  13  detects the load from, for example, an average output value of the four strain gauge sensors  31 . In addition, the vibration unit  14  drives, for example, two piezoelectric vibrators  32  in phase. 
     Here, the predetermined standard used for detection at step S 81  is, for example, the load at the point B shown in  FIG. 1 . Accordingly, this predetermined standard may be appropriately set in accordance with the load characteristics of an intended push-button switch in pressing. For the mobile terminals, for example, the predetermined standard may be set by users as desired such that elder users may set it heavier, whereas users who often write messages may set it lighter. In addition, the predetermined drive signal to drive the vibration unit  14  at step S 82 , that is, a frequency, period (wavelength), waveform and vibration amplitude to stimulate the tactile sensation may be set appropriately according to the click sensation to be provided. For example, in order to provide the click sensation represented by the metal dome switch used for the mobile terminals, at a point when the predetermined load is applied on the touch panel  12 , the vibration unit  14  is driven by a drive signal, for example a sine wave with a constant frequency of 170 Hz, for 1 period so as to vibrate the touch panel  12  by approximately 15 μm while a predetermined load is being applied thereon, as stated below. Thereby, it is possible to provide the operator with the realistic click sensation. 
     Then, when detecting that the load detected by the load detection unit  13  satisfies the predetermined standard (step S 83 ), the control unit  15  drives the vibration unit  14  with a predetermined drive signal in the same manner as in pressing, in order to vibrate the touch panel  12  in a predetermined vibration pattern (step S 84 ). 
     Here, the predetermined standard load in releasing at step S 83 , that is, detected after a pressure input is received, is set to be lower than the load detected in pressing at step S 81 , preferably at any value in a range of 50-80% of the load in pressing, as described below. The drive signal to drive the vibration unit  14  in releasing at step S 84  may be either equal to or different from the drive signal in pressing at step S 82 . For example, the frequency of the drive signal in pressing at which an input to the touch panel  12  is received may be set to 170 Hz, and the frequency of drive signal in releasing may be set to 125 Hz as shown in  FIG. 4 , for example. 
     As set forth above, the input apparatus according to the present embodiment stimulates the pressure sensation until the load applied to the touch panel  12  and detected by the load detection unit  13  satisfies the predetermined standard for receiving an input to the touch panel  12  and, when the predetermined standard is satisfied, stimulates the tactile sensation by driving the vibration unit  14  with the predetermined drive signal such that the touch panel  12  is vibrated in the predetermined vibration pattern. Thereby, the input apparatus provides the operator with the click sensation such that the operator recognizes that the input operation is completed. Accordingly, being able to perform the input operation with feeling the realistic click sensation similar to that obtained when operating the push-button switch, the operator may not have the feeling of strangeness. Moreover, since the operator performs the input operation in conjunction with a perception to “have tapped” the touch panel  12 , it prevents erroneous inputs caused by mere tapping. 
     In addition, the input apparatus according to the present invention drives the vibration unit  14  with a predetermined drive signal in releasing after the pressure input is received, in the same manner as that in pressing if a load satisfies a standard lower than the predetermined standard for receiving a pressure input, in order to vibrate the touch panel  12  in a predetermined vibration pattern. Thereby, it is possible to provide the release tactile sensation to the operator. 
     For example, in a case where the standard of the load of pressing to drive the vibration unit  14  and that of releasing are set to be equal, it is possible to provide the click sensation in pressing and in releasing as shown in  FIG. 8  if a maximum load in pressing exceeds the standard load. Accordingly, it is possible to provide the operator with the click sensation more similar to that of the push-button switch. However, if the object pressing the input unit is pulled back at the standard load of pressing, it is concerned that the vibration unit  14  may not be vibrated in releasing or an unexpected release tactile sensation may be provided when the operator intends to maintain the pressure load at the standard load, giving the operator the feeling of strangeness. 
     In contrast, since the input apparatus according to the present embodiment sets the standard load of releasing to drove the vibrating unit  14  at a value lower than that of pressing, it ensures to provide the operator with the release tactile sensation in releasing, and thus it is possible to provide the click sensation more closer to the push-button switch. Especially if the predetermined standard load of releasing to drive the vibration unit  14  is set at a value in the range of 50-80% of that of pressing to drive the vibration unit  14 , it enables a smooth continuous input operation with realistic click sensation during continuous input of the same input object on the touch panel  12 . It is to be noted that, in  FIG. 8 ,  FIG. 9  and other figures, “Cli” and “Ck” represent the click sensation the human feels. 
     Second Embodiment 
       FIG. 10  and  FIG. 11  illustrate an input apparatus according to a second embodiment of the present invention;  FIG. 10  is a block diagram of a schematic constitution and  FIG. 9  is a front view thereof. This input apparatus is mounted on, for example, a mobile terminal and, as shown in  FIG. 10 , has a touch panel  41  as the input unit for receiving a pressure input, a position detection unit  42  for detecting an input position on the touch panel  41 , a display panel  43  for displaying information based on the input position detected by the position detection unit  42 , a load detection unit  44  for detecting a pressure load on the touch panel  41 , a vibration unit  45  for vibrating the touch panel  41  and a control unit  46  for controlling overall operations. 
     As shown in  FIG. 11 , a plurality of input objects  41   a  such as numeric keys are already provided on the touch panel  41  by printing, a sticker and the like. For each input object  41   a , in order to prevent an erroneous input to press a plurality of adjacent input objects  41   a , an effective pressing area for receiving an input is set to be smaller than a disposition area of the input object  41   a . It is to be noted that, in  FIG. 10 , the load detection unit  44  and the vibration unit  45  have strain gauge sensors and piezoelectric vibrators, respectively, in the same manner as those of the input apparatus shown in  FIG. 6 . 
     The control unit  46  monitors an input to the touch panel  41  and a load detected by the load detection unit  44 , as well as monitoring an input position on the touch panel  41  detected by the position detection unit  42 . When the position detection unit  42  detects an input position in the effective pressing area of the input object, and when a pressure load detected by the load detection unit  44  increases with a pressure on the touch panel  41  and satisfies a predetermined standard for receiving an input, the vibration unit  45  is driven with a predetermined drive signal to vibrate the touch panel  41  in a predetermined vibration pattern. 
     That is, if the position detection unit  42  detects the input position in the effective pressing area of the input object, the control unit  46 , in the same manner as that of the input apparatus according to the first embodiment, drives the vibration unit  45  with a drive signal, for example a sine wave with a constant frequency of 170 Hz, for 1 period at a point when the load on the touch panel  41  increases and satisfies the predetermined standard, in order to vibrate the touch panel  41  by approximately 15 μm while the predetermined load is being applied thereon. Thereby, the operator is provided with the click sensation so as to recognize that the input operation is completed. In addition, by receiving the input detected on the touch panel  41 , the control unit  46  displays according to the input on the display panel  43 . 
     Subsequently, when detecting that the load detected by the load detection unit  44  satisfies a predetermined standard of releasing lower than the predetermined standard for receiving an input to the touch panel  41  in the same manner as that according to the first embodiment, the control unit  46  drives the vibration unit  45  with a predetermined drive signal in order to vibrate the touch panel  41  in a predetermined vibration pattern. 
     Hence, according to the input apparatus according to the present invention, in the same manner as the first embodiment, since being able to perform the input operation on the touch panel  41  with feeling the realistic click sensation which is the same as that obtained when operating the push-button switch, the operator does not have the feeling of strangeness. Moreover, since the operator performs the input operation in conjunction with the perception to “have tapped” the touch panel  41 , it prevents erroneous inputs caused by mere tapping. 
     In addition, the input apparatus according to the present embodiment drives the vibration unit  45  with the predetermined drive signal in releasing after the pressure input is received, in the same manner as that in pressing, if the load satisfies the predetermined standard lower than the predetermined standard for receiving a pressure input, in order to vibrate the touch panel  41  in the predetermined vibration pattern. Thereby, it ensures to provide the release tactile sensation. Therefore, the input apparatus according to the present embodiment is capable of providing the click sensation in combination with the click sensation in pressing, more closer to that of the push button switch. Especially if the predetermined standard load of releasing to drive the vibration unit  14  is set at a value in the range of 50-80% of that of pressing to drive the vibration unit  14 , it enables a smooth continuous input operation with receiving realistic click sensation. 
     The following is description of the results of sensory evaluations on the click sensation of the input apparatus according to each of the above embodiments examined by the inventors. 
     According to measurements by the inventors, the metal dome switches widely used for commercially available mobile terminals, although there are deviations to some degrees according to models, have the load characteristics that the load is rapidly decreased when a predetermined load, roughly equal to or less than 6 N and generally equal to or less than 3 N, is applied thereto. As such, the inventors conducted sensory evaluations of the click sensation of the input apparatus designed as shown in  FIG. 5  and  FIG. 6  by vibrating the vibration unit  14  only in pressing. In these sensory evaluations, a load (load at the point B in  FIG. 1 ) on the touch panel  12  for starting drive of the vibration unit  14  in pressing was set at 1.5 N and the frequency, the period (wavelength) and the waveform of the drive signal are used as parameters. 
     Exemplary results of the evaluations are shown in  FIG. 12  to  FIG. 15 . In  FIG. 12  to  FIG. 15 , the subjects were the five people involved in the sensory evaluations shown in  FIG. 2  and  FIG. 3 . Three evaluation items were “feel click sensation”, “good feeling” and tactile sensation “similar to mobile terminal”. For the item “feel click sensation”, “No” scores 1 and “Strongly feel” scores 7. For the item “good feeling”, “Bad” scores 1 and “Good” scores 7. For the item “similar to mobile terminal”, “not similar” scores 1 and “very similar” scores 7. The score of each item represents an average score of the five people. 
       FIG. 12  shows results of evaluations when varying the frequency. In the sensory evaluations, the period (wavelength) of the drive signal to drive the vibration unit  14 , that is, the drive time was 1 period, the waveform was the sine wave and the frequency was varied in a range of 50-250 Hz. The amplitude of the drive signal was set to a level at which the vibration amplitude of 15 μm can be obtained in a state of a predetermined standard load being applied on the touch panel  12 . As can be seen in  FIG. 12 , it was confirmed that, although the highest evaluation was obtained at the frequency of 170 Hz, the human can obtain the click sensation similar to that of the mobile terminals at a frequency of 140 Hz or higher. 
       FIG. 13  shows results of evaluations when varying the amplitude of the drive signal. In the sensory evaluations, the frequency of the drive signal to drive the drive unit  14  was 170 Hz, the period was 1 period and the waveform was the sine wave. The signal amplitude was varied such that, in a state with no load in which the touch panel  12  was not pressed, the touch panel  12  is vibrated with predetermined amplitude in a range of 1-35 μm. Under a condition of the vibration amplitude with no load, the drive unit  14  was driven when a load of 1.5 N was applied to the touch panel  12  in order to evaluate according to each item. A horizontal axis in  FIG. 13  represents the vibration amplitude when the load of 1.5 N was applied corresponding to that with no load. As a result, as can be seen in  FIG. 13 , it was confirmed that, in a state with the load of 1.5 N, the human can sufficiently obtain the click sensation if the vibration amplitude is 15 μm or more. That is, it was confirmed that the human can obtain the click sensation by, in a state with the load of 1.5 N on the touch panel  12 , a vibration of the touch panel  12  only 1 period with the constant frequency of 170 Hz with the vibration amplitude of 15 μm or more. 
       FIG. 14  shows results of evaluations when varying the period (wavelength), that is, drive time. In the sensory evaluations, the waveform of the drive signal to drive the vibration unit  14  was the sine wave, the signal amplitude was set to a level which causes the vibration amplitude of 15 μm in a state of the predetermined standard load being applied on the touch panel  12 , the frequency was 170 Hz and the period was varied in a range of ¼ to 3 periods. For ¼ period and ½ period, the signal amplitude was set such that a vibration displacement on the touch panel  12  was approximately the same as those in other periods, that is, to a level at which the vibration amplitude of approximately 15 μm can be obtained. As a result, as can be seen in  FIG. 14 , the highest evaluation was obtained when the period (wavelength) was 1 period. In addition, it was also confirmed that, although basically good results were obtained in 5/4 periods and less than 1 period, it differed from the click sensation of the mobile terminal in 3/2 or more periods. 
       FIG. 15  shows results of evaluations when varying of the waveform of the drive signal. In the sensory evaluations, a sine wave, a square wave and a triangle wave were used as the waveform of the drive signal to drive the vibration unit  14 . In addition, the frequency of each signal is 170 Hz, the signal amplitude was set to a level which causes the vibration amplitude of 15 μm in the state of the predetermined standard load being applied to the touch panel  12 , and the period was 1 period. As a result, as can be seen in  FIG. 15 , the highest evaluation was obtained by the sine wave. 
     Here, the drive signal of the sine wave (input voltage of the drive unit  14 ), as shown by a dashed line in  FIG. 16 , may be the voltage in 1 period from any phase not only 1 period in which the voltage increases from 0 degree phase and then decreases but also, such as, 1 period in which the voltage decreases from 180 degree phase and then increases.  FIG. 16  also shows a waveform (broken line) of the vibration amplitude of the touch panel  12  under no load and a waveform (solid line) of the vibration amplitude of the touch panel  12  under a load of 1.5 N when the drive unit  14  is driven by the input voltage shown by the dashed line. 
     From the exemplary results of the evaluations described above, it was confirmed that, when the input apparatus designed as shown in  FIG. 5  and  FIG. 6  is applied to a mobile terminal, it is possible to provide the operator with the realistic click sensation if the touch panel  12  is vibrated by approximately 15 μm or more with the drive signal, for example 5/4 period or less, preferably 1 period of the sine wave with the constant frequency of 140 Hz or more, preferably 170 Hz, at a point when a load satisfying the predetermined standard is applied to the touch panel  12  in pressing. It was also confirmed that the same results could be obtained by the input apparatus designed shown in  FIG. 10  and  FIG. 11 . 
     Next, the inventors conducted sensory evaluations on the click sensation when the vibration unit  14  was driven only in pressing as described above and when it was driven both in pressing and in releasing. The following is a description of results of these evaluations. 
       FIG. 17  is a diagram illustrating exemplary results of such evaluations. In  FIG. 17 , bars on the left side represent results of the evaluations when the vibration unit  14  was driven only in pressing, that is, “without the release tactile sensation”, whereas bars on the right side represent results of the evaluations when the vibration unit  14  was driven both in pressing and in releasing, that is, “with the release tactile sensation”. The subjects were the five people involved in the sensory evaluations shown in  FIG. 2  and  FIG. 3 . Evaluation items were four items including “good feedback (easy to percept)” in addition to the three evaluation items in  FIG. 12  to  FIG. 15 . Each item is on a scale of 1 to 7 and the score of each item represents an average score of the five people. For the item “good feedback”, “bad” scores 1 and “good” scores 7. In addition, the predetermined standard loads of pressing and that of releasing to drive the vibration unit  14  were equal and the drive signals in pressing and that in releasing were also equal. Here, the predetermined standard load was 1.5 N. In addition, the drive signal was 1 period of the sine wave with the frequency of 170 Hz so as to vibrate the touch panel  12  under the pressure of 1.5 N by approximately 15 μm. 
     As can be seen in the results of the evaluations in  FIG. 17 , it was confirmed that, if the release tactile sensation is provided by vibrating the touch panel  12  in releasing as well, the click sensation becomes more similar to that of the mobile terminals and a good feedback (perception) can be obtained. It was also confirmed that the same results can be obtained by the input apparatus having a constitution shown in  FIG. 10  and  FIG. 11 . 
     The inventors further conducted sensory evaluations on the click sensation for continuous inputs when the click sensation is provided both in pressing and in releasing as described above. The following is a description of results of these evaluations. 
     For example, when the human quickly performs the continuous input, a next input is generally started before the pressure load returns to “0” and the maximum load in pressing varies. In such a case, if the predetermined standard load of pressing to drive the vibration unit  14  and that of releasing are set to be equal, it may cause a phenomenon as shown in  FIG. 18 . That is, if the pressure load is pulled back at the standard load during the repetitive tap, upon this input the vibration unit  14  may not be driven in releasing or the click sensation may be provided before the operator recognizes to have released. As a result, the input operation and the click sensation do not synchronize possibly giving the operator the feeling of strangeness.  FIG. 18  shows a case where a pressure load on a third input in four continuous inputs is pulled back from the standard load. 
     On the other hand, if the predetermined standard load of releasing to drive the vibration unit  14  is set too low in comparison with the load to drive the vibration unit  14  in pressing, a phenomenon as shown in  FIG. 19  may be caused. That is, if a next input is performed before the load returns to the predetermined standard load of releasing during the repetitive tap, the sensation is not provided in synchronization. As a result, it may give the operator the feeling of strangeness.  FIG. 19  shows a case where a third input in a four repetitive taps is performed before a load of releasing on a second input reaches the standard load of releasing. In addition, if the predetermined standard load of releasing is too low as stated above, it takes time to return thereto. As a result, the operator does not feel the feeling of strangeness by the tactile sensation provided but it takes time to allow a next input and thus prevents the operator from operating quick continuous input even if the operator desires it. Thereby, there is a concern that it may deteriorate operability at the continuous input (repetitive tap). 
     In contrast, if the predetermined standard load of releasing to drive the vibration unit  14  is set close to the load to drive the vibration unit  14  in pressing, it enables quicker continuous input. However, if the operator tries to maintain a pressed state (hold) during the continuous input, an unexpected release tactile sensation may be provided to the operator giving the feel of strangeness. That is, when the pressed state is held during the continuous input, the load slightly varies even though the operator intends to maintain the pressure load constant. Therefore, as shown in  FIG. 20 , for example, if a load range between the standard load of pressing and that of releasing is smaller than a load variation range in a holding state as described above, the operator is provided with the release tactile sensation despite thinking oneself holding and thus has the feeling of strangeness. 
     As such, the inventors conducted sensory evaluations on the click sensation with various loads to drive the vibration unit  14  in releasing, to the load to drive the vibration unit  14  in pressing. 
       FIG. 21  to  FIG. 23  are diagrams illustrating the results of these evaluations. In  FIG. 22  to  FIG. 24 , the subjects were the five people involved in the sensory evaluations shown in  FIG. 17 . Evaluation items were five items including “easy for repetitive tap” in addition to the four items in  FIG. 17 . Each item is on a scale of 1 to 7 and the score of each item represents an average score of the five people. For the item “easy for repetitive tap”, “No” scores 1 and “Yes” scores 7. In addition, both in pressing and in releasing, the drive signal to drive the vibration unit was 1 period of the sine wave with the frequency of 170 Hz so as to vibrate the touch panel by approximately 15 μm when each predetermined standard was satisfied. 
       FIG. 21  shows results of evaluations when the predetermined standard load of pressing was 1 N and the predetermined standard load of releasing was 0 N, 0.5 N and 1 N. As can be seen in  FIG. 21 , if the predetermined standard load of pressing to start vibration was 1 N, the highest evaluations for all items were obtained when the predetermined standard load of releasing to start vibration was 0.5 N. 
       FIG. 22  shows results of evaluations when the predetermined standard load of pressing was 2 N and the predetermined standard load of releasing was 0 N, 0.5 N, 1 N, 1.5 N and 2 N. As can be seen in  FIG. 22 , if the predetermined standard load of pressing to start vibration was 2 N, high evaluations were obtained when the predetermined standard load of releasing to start vibration was 1 N and 1.5 N. The highest evaluations for all items were obtained especially with 1.5 N. 
       FIG. 23  shows results of evaluations when the predetermined standard load of pressing was 3 N and the predetermined standard load of releasing was 0 N, 0.5 N, 1 N, 1.5 N, 2 N, 2.5 N and 3 N. As can be seen in  FIG. 23 , if the predetermined standard load of pressing to start vibration was 3 N, high evaluations were obtained when the predetermined standard load of releasing to start vibration was 1.5 N, 2 N and 2.5 N. The highest evaluations for all items were obtained especially with 2 N. 
     From the exemplary results of the evaluations described above, it was confirmed that, if the predetermined standard load of releasing to drive the vibration unit is set at a value in the range of 50-80% of that of pressing, it is possible to synchronize sequential inputs and timings to provide the feeling during the continuous input (repetitive tap), and thus the realistic click sensation can be provided without giving the feeling of strangeness. That is, the predetermined standard load of releasing is set to be smaller than but equal to or over 50% of that of pressing. Thereby, the operability at the continuous input is dramatically improved without giving the feeling of strangeness. In addition, the predetermined standard load of releasing is set to be equal to or under 80% of that of pressing. Thereby, it is possible to deal with slight variations in the load in the holding state during the continuous input. 
     Accordingly, if the predetermined standard load of pressing is set 1 N, for example, that of releasing is set at any value from 0.5 N to 0.8 N. In addition, if the predetermined standard load of pressing is high, the load variation range in the holding state is wider than that when the predetermined standard load is low. In such a case also, the predetermined standard load of releasing is set in the range of 50-80% of that of pressing. For example, if the predetermined standard load of pressing is set high, 6 N, the predetermined standard load of releasing is set to 3N-4.8 N. Thereby, it is possible to provide the realistic click sensation in synchronization with the continuous input without providing unexpected release tactile sensation and giving the feeling of strangeness. The predetermined standard load of pressing and that of releasing may be set either fixedly or selectively arbitrarily by the user. 
     It is to be understood that the present invention is not limited to the embodiments set forth above, and various modifications and changes may be implemented. For example, the load detection unit may be constituted of any number of strain gauge sensors. In addition, the load detection unit may be constituted according to an input detection scheme of the touch panel. For example, the load detection unit can be constituted without using the strain gauge sensor if the load can be detected from a change of an output signal based on a resistance change in accordance with a contact area in a case of employing the resistive film scheme or on a change in capacitance in a case of employing the capacitive scheme. In addition, the vibration unit may be constituted of any number of piezoelectric vibrators, transparent piezoelectric elements provided on an entire operation surface of the touch panel, or an eccentric motor which rotates 360 degrees in 1 period of the drive signal. 
     In addition, if the input apparatus has the display panel as shown in  FIG. 5  and  FIG. 6 , the control unit may control so as to change a display state of a corresponding input object on the display panel by inversion or the like, upon receiving an input to the touch panel. Moreover, the control unit may be configured to change the drive signal to drive the vibration unit based on an input position detected on the touch panel so as to change the click sensation. 
     The present invention is applicable to an input apparatus with an input unit serving as one switch. Also, the input apparatus according to the present invention is capable of providing feelings of a multistep switch, such as a two-step switch (pressed further after pressed), by sequentially providing the click sensations on different standards (loads) while the input unit is being pressed. Thereby, if the input apparatus is applied to a release button of a camera, for example, it is possible to provide a feeling to lock focus (first step) and a feeling to release (second step). In addition, in combination with the display unit, it is possible to change a display of a menu screen and the like in a variety of manners in accordance with the step. Moreover, when providing the feelings of the multistep switch, it is possible to change the drive signal to vibrate the input unit by the vibration unit at each step in order to provide a different click sensation at each step. 
     According to the present invention, the vibration unit is driven when the pressure load detected by the load detection unit satisfies a predetermined standard for receiving an input. Here, “when the pressure load detected by the load detection unit satisfies the predetermined standard for receiving an input” may represent “when the pressure load detected by the load detection unit reaches the predetermined value for receiving the input”, “when the pressure load detected by the load detection unit exceeds the predetermined value for receiving the input”, or “when a predetermined value for receiving an input is detected by the load detection unit”. 
     The control unit vibrates the input unit (touch panel) in the predetermined vibration pattern by driving the drive unit when the pressure load detected by the load detection unit satisfies the predetermined standard, and such predetermined vibration pattern in pressing may be one as shown by the solid line in  FIG. 4 , whereas that in releasing may be another as shown by the dashed line in  FIG. 4 . Vibration of the input unit in those manners enables to provide the operator with the click sensation (vibration stimulus) the same as that obtained when operating the push-button switch. 
     REFERENCE SIGNS LIST 
     
         
           11  display panel 
           12  touch panel 
           13  load detection unit 
           14  vibration unit 
           15  control unit 
           21  housing 
           22  insulator 
           23  upper cover 
           24  insulator 
           31  strain gauge sensor 
           32  ultrasonic transducer 
           41  touch panel 
           41   a  input object 
           42  position detection unit 
           43  display panel 
           44  load detection unit 
           45  vibration unit 
           46  control unit