Patent Publication Number: US-2015068306-A1

Title: Movable device having drop resistive protection

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 102132602, filed on Sep. 10, 2013. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     1. Technical Field 
     The invention relates to a movable device. Particularly, the invention relates to a movable device having drop resistive protection. 
     2. Related Art 
     In recent years, along with development of electronic products such as smart phones, tablet PCs and somatosensory game machines, etc., micro-electromechanical system (MEMS) inertial sensors such as accelerometers and gyroscopes, etc. are widely applied in the aforementioned electronic products, and a market demand thereof has grown significantly year by year. Under intense market competition, related applications of the MEMS inertial sensors have higher demand on quality of the MEMS inertial sensors. Regarding a piezo-resistive accelerometer, acceleration of an apparatus is measured through a resistance variation amount of a component therein. 
       FIG. 1  is a cross-sectional view of a conventional MEMS accelerometer.  FIG. 2  is a top view of a part of components of the accelerometer of  FIG. 1 . Referring to  FIG. 1  and  FIG. 2 , the conventional accelerometer  50  is, for example, a piezo-resistive accelerometer, in which a mass  52  is connected to a connection portion  56   a  of a base  56  through an elastic portion  54 . When an apparatus having the accelerometer  50  withstands an external force, the mass  52  is moved and the elastic portion  54  is elastically deformed, and a resistance variation caused by the elastic deformation of the elastic portion  54  can be used to calculate an acceleration of the apparatus, and the detection and calculation principles are known techniques in the field. For example, U.S. Pat. No. 4,967,605 discloses related techniques of a MEMS accelerometer. 
     When the apparatus drops, if the mass  52  in the accelerometer  50  instantly generates a large displacement due to an impact force of the drop, the elastic portion  54  is probably damaged due to excessive pulling. In this way, in some drop resistive designs, a moving range of the mass  52  can be limited by decreasing a gap G 1  between a first base body  56   b  and the mass  52  and decreasing a gap G 2  between a second base body  56   c  and the mass  52 , so as to avoid the mass  52  from instantly generating a large displacement due to the impact force caused by drop of the mass  52 . However, along with miniaturization of the MEMS accelerometer, due to a size error generated when the first base body  56   b  and the second base body  56   c  are adhered to the connection portion  56   a  through an adhesive  58   a  and an adhesive  58   b,  the gap G 1  and the gap G 2  are hard to be accurately formed, such that the drop resistive protection cannot be substantially achieved, especially, there is none lateral drop resistive mechanism, which is a main damage mode of the product. 
     SUMMARY 
     The invention is directed to a movable device, which has a good impact and drop resistive protection function. 
     The invention provides a movable device including a base, a mass, a plurality of elastic portions and at least one block structure. The mass has a plurality of side surfaces. The elastic portions are connected to the side surfaces respectively and connected to the base, where the mass is adapted to move such that the elastic portions are elastically deformed. The block structure is disposed at the base and is aligned to at least one of the side surfaces, where the block structure is adapted to block the corresponding side surface to limit a moving range of the mass. 
     In an embodiment of the invention, the base includes a first base body, a second base body and a connection portion. The mass is located between the first base body and the second base body, and the block structure is fixed to the first base body or the second base body. The connection portion is fixed between the first base body and the second base body, where each of the elastic portions is connected between the corresponding side surface and the connection portion. 
     In an embodiment of the invention, the connection portion is adhered to the first base body in a first direction, the connection portion is adhered to the second base body in the first direction, and each of the side surfaces is parallel to the first direction. 
     In an embodiment of the invention, a number of the at least one block structure is plural, and the block structures are respectively aligned to the side surfaces. 
     In an embodiment of the invention, the block structure has two block surfaces, and the two block surfaces are respectively aligned to the two adjacent side surfaces. 
     In an embodiment of the invention, the block structure extends from the base in a first direction, and a length of the block structure in the first direction is greater than a gap between the mass and the base in the first direction. 
     In an embodiment of the invention, the movable device further includes at least one block portion, where the mass has at least one end surface, the block portion is disposed on the base and extends towards the end surface and is aligned to the end surface, the mass is adapted to move in a first direction such that the elastic portions are elastically deformed, a gap between the base and the end surface in the first direction is greater than a gap between the block portion and the end surface in the first direction, and the block portion is adapted to block the end surface to limit the moving range of the mass. 
     In an embodiment of the invention, the block structure extends from the block portion. 
     In an embodiment of the invention, a length of the block structure in the first direction is greater than a gap of the block portion and the end surface in the first direction. 
     In an embodiment of the invention, a number of the at least one block portion is plural, and the at least one end surface includes a top surface of the mass and a bottom surface of the mass, a part of the block portions is aligned to the top surface, and another part of the block portions is aligned to the bottom surface. 
     In an embodiment of the invention, the mass has at least one end surface, the end surface is perpendicular to each of the side surfaces, the block structure is adapted to block the corresponding side surface to limit a moving range of the mass in a second direction, and the second direction is inclined to each of the side surfaces and the end surface. 
     In an embodiment of the invention, each of the elastic portions extends in an axis, and the axis does not pass through a mass center of the mass. 
     In an embodiment of the invention, the block structure is formed through an exposure process and an etching process. 
     According to the above descriptions, the movable device has block structures on the base, and the block structures are capable of blocking the side surfaces of the mass to limit the moving range of the mass, such that the mass is avoided to have an instant large displacement due to an impact force of drop, so as to avoid a pulling damage of the elastic portions due to excessive displacement of the mass. The block structures can be formed through an exposure process and an etching process to achieve a better size accuracy, such that the block structures and the side surfaces of the mass have suitable gaps there between to achieve an effect of accurately limiting the moving range of the mass, so as to improve the drop resistive protection function of the movable device. 
     In order to make the aforementioned and other features and advantages of the invention comprehensible, several exemplary embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a cross-sectional view of a conventional MEMS accelerometer. 
         FIG. 2  is a top view of a part of components of the accelerometer of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a movable device according to an embodiment of the invention. 
         FIG. 4  is a top view of a part of components of the movable device of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of a movable device according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS 
       FIG. 3  is a cross-sectional view of a movable device according to an embodiment of the invention.  FIG. 4  is a top view of a part of components of the movable device of  FIG. 3 . Referring to  FIG. 3  and  FIG. 4 , the movable device  100  of the present embodiment is, for example, a MEMS accelerometer, and includes a base  110 , a mass  120  and a plurality of elastic portions  130 . The base  110  includes a first base body  112 , a second base body  114  and a connection portion  116 , where the connection portion  116  is fixed between the first base body  112  and the second base body  114 . The mass  120  is located between the first base body  112  and the second base body  114  and has a plurality of side surfaces  120   a  and two end surfaces opposite to each other, where the two end surfaces are respectively a top surface  120   b  and a bottom surface  120   c  of the mass  120 , which are perpendicular to each of the side surfaces  120   a.    
     The elastic portions  130  are respectively connected to the side surfaces  120   a  and connected to the connection portion  116  of the base  110 . When an apparatus having the accelerometer  100  withstands an external force, the mass  120  is moved and the elastic portions  130  are is elastically deformed, and a resistance variation caused by the elastic deformation of the elastic portions  130  can be used to calculate an acceleration of the apparatus, and detection and calculation principles thereof are known techniques in the field, which are not repeated. 
     The movable device  100  of the present embodiment further includes a plurality of block structures  140 . A part of the block structures  140  is fixed to the first base body  112 , and another part of the block structures  140  is fixed to the second base body  114 . As that shown in  FIG. 3 , the block structures  140  extend from the base  110  in a first direction D 1 , and a length of each of the block structures  140  in the first direction D 1  is greater than a gap G 3  and a gap G 4  between the mass  120  and the base  110  in the first direction D 1 , such that the block structures  140  can be respectively aligned to the side surfaces  120   a  of the mass  120 , where each of the block structures  140 , for example, has two block surfaces  140   a,  and the two block surfaces  140   a  are respectively aligned to two adjacent side surfaces  120   a.    
     Under the above configuration, the block structures  140  can block the side surfaces  120   a  to limit a moving range of the mass  120 , such that the mass  120  is avoided to have an instant large displacement due to an impact force of drop, so as to avoid a pulling damage of the elastic portions  130  due to excessive displacement of the mass  120 . The block structures  140  can be formed through an exposure process and an etching process to achieve a better size accuracy, such that the block structures  140  and the side surfaces  120   a  of the mass  120  have suitable gaps there between to achieve an effect of accurately limiting the moving range of the mass  120 , so as to improve the drop resistive protection function of the movable device  100 . 
     Further, the connection portion  116  is adhered to the first base body  112  through an adhesive  150   a  in the first direction D 1  shown in  FIG. 3 , the connection portion  116  is adhered to the second base body  114  through an adhesive  150   b  in the first direction D 1 , and each of the side surfaces  120   a  of the mass  120  is parallel to the first direction D 1 . In this way, a size error in the first direction D 1  generated when the first base body  112  and the second base body  114  are adhered to the connection portion  116  is less likely to influence the accuracy of the gap between each of the side surfaces  120   a  and the corresponding block structure  140 . 
     In the present embodiment, a part of the elastic portions  130  extends in an axis A 1  (shown in  FIG. 3  and  FIG. 4 ), and another part of the elastic portions  130  extends in an axis A 2  (which is only shown in  FIG. 4 ), and the axis A 1  and the axis A 2  do not pass through a mass center M of the mass  120 . In this way, when the mass  120  withstands the impact force of drop, the mass  120  is liable to have a displacement in an inclining direction. The inclining direction is, for example, the second direction D 2  shown in  FIG. 3  or other inclining directions inclined to the side surfaces  120   a,  the top surface  120   b  and the bottom surface  120   c  of the mass  120 . When the mass  120  has a displacement in the inclining direction, the block structure  140  is adapted to block the side surface  120   a  of the mass  120  to limit the moving range of the mass  120  in the inclining direction, so as to avoid a pulling damage of the elastic portions  130  due to excessive displacement of the mass  120  in the first direction D 1 . 
       FIG. 5  is a cross-sectional view of a movable device according to another embodiment of the invention. In the movable device  200  of  FIG. 5 , configuration and functions of a base  210 , a first base body  212 , a second base body  214 , a connection portion  216 , a mass  220 , elastic portions  230 , block structures  240 , an adhesive  250   a  and an adhesive  250   b  are similar to that of the base  110 , the first base body  112 , the second base body  114 , the connection portion  116 , the mass  120 , the elastic portions  130 , the block structures  140 , the adhesive  150   a  and the adhesive  150   b,  which are not repeated. A difference between the movable device  200  and the movable device  100  is that the movable device  200  is integrated with a gyroscope function, and the mass  220  is further driven in a first direction D 1 ′ to resonate to elastically deform the elastic portions  230 , and a Coriolis force of the movable device  200  during rotation can be measured through the resonation operation method, so as to calculate an angular speed of an apparatus having the movable device  200 , where the detection and calculation principles are known techniques in the field, which are not repeated. 
     The movable device  200  further includes a plurality of block portions  260 , where a part of the block portions  260  is fixed to the first base body  212  and extends towards the top surface  220   b  of the mass  220  and is aligned to the top surface  220   b , another part of the block portions  260  is fixed to the second base body  214  and extends towards the bottom surface  220   c  of the mass  220  and is aligned to the bottom surface  220   c.  A gap G 5  between the base  210  and the top surface  220   b  of the mass  220  in the first direction D 1 ′ is greater than a gap G 7  between the block portion  260  and the top surface  220   b  of the mass  260  in the first direction D 1 ′, and a gap G 6  between the base  210  and the bottom surface  220   c  of the mass  220  in the first direction D 1 ′ is greater than a gap G 8  between the block portion  260  and the bottom surface  220   c  of the mass  260  in the first direction D 1 ′. 
     Under such configuration, the block portion  260  is adapted to block the top surface  220   b  and the bottom surface of the mass  220  to limit the moving range of the mass  220 , such that the mass  220  is avoided to have an instant large displacement due to an impact force of drop, so as to avoid a pulling damage of the elastic portions  230  due to excessive displacement of the mass  220 , and achieve the drop resistive protection function. As that described above, in the movable device  200 , since the block portion  260  on the base  210  is used to block the mass  220  to limit the moving range of the mass  220 , it is unnecessary to decrease the gaps between the whole base  210  and the top surface  220   b  and the bottom surface  220   c  of the mass  220  for blocking the mass  220 , such that the base  210  and the mass  220  may have larger gaps G 5  and G 6  there between. In this way, a damping effect caused by the air between the base  210  and the mass  220  is not excessive, so as to ensure a smooth resonance of the mass  220 . In other embodiments, the movable device  200  can also be a quartz crystal oscillator or other resonance devices, which is not limited by the invention. 
     In the present embodiment, the block structures  240 , for example, respectively extend from the block portions  260 , and a length of the block structure  240  in the first direction D 1  is greater than the gap G 7  between the block portion  260  and the top surface  220   b  of the mass  220  in the first direction D 1 ′ and is greater than the gap G 8  between the block portion  260  and the bottom surface  220   c  of the mass  220  in the first direction D 1 ′, such that the block structures  240  can be respectively aligned to the side surfaces  220   a  of the mass  220  to limit the moving range of the mass  220 . 
     In summary, the movable device of the invention has block structures on the base, and the block structures are capable of blocking the side surfaces of the mass to limit the moving range of the mass, such that the mass is avoided to have an instant large displacement due to an impact force of drop, so as to avoid a pulling damage of the elastic portions due to excessive displacement of the mass. The block structures can be formed through an exposure process and an etching process to achieve a better size accuracy, such that the block structures and the side surfaces of the mass have suitable gaps there between to achieve an effect of accurately limiting the moving range of the mass, so as to improve the drop resistive protection function of the movable device. Moreover, the block portions can be configured on the base of the movable device for blocking the end surfaces of the mass to limit the moving range of the mass, so as to further improve the drop resistive protection function. By configuring the block portions, it is unnecessary to decrease the gaps between the base and the end surfaces of the mass for blocking the mass. In this way, a damping effect caused by the air between the base and the end surface of the mass is not excessive, so as to ensure a smooth resonance of the mass. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.