Abstract:
A small, efficient and stable ultrasonic motor is provided, wherein force is prevented from varying before and after assembly and can be adjusted after assembly without requiring troublesome operations. An electronic apparatus with such a ultrasonic motor is also provided. The ultrasonic motor has a force applying device for applying a force to a vibrating member to be vibrated and to a moving member placed in abutment against the vibrating member to cause a frictional force therebetween so that the moving member is driven by the frictional force. The force applying device comprises a main force applying device for applying a main force and a force adjusting elements for adjusting the force applied by the main force applying device. In one embodiment, the main force applying device is a leaf spring and the force applying elements are slits formed in the leaf spring and strips formed between the slits. Adjustment of the force applied by the leaf spring is performed by removing one or more of the strips.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an ultrasonic motor having a force applying means for applying a force to a vibrating member and moving member, and more particularly to an ultrasonic motor having a force applying means for applying a force to be adjusted before or after assembling the vibrating member, moving member and so on, and to an electronic apparatus with such a ultrasonic motor. 
     In the field of micro-motors, attention has recently been drawn to ultrasonic motors that utilize a piezoelectric effect provided by a piezoelectric element. 
     There is known, as one example of such an ultrasonic motor, a type that is provided with a support plate, a center shaft fixed to the support plate, a vibrating member fixed on the center shaft, a piezoelectric element joined to an underside of the vibrating member, a moving member placed in abutment against a projection provided on the vibrating member, and a force applying means placed in pressure contact with the moving member. 
     According to this art, the piezoelectric element is vibrated so that the vibration of the piezoelectric element causes the vibrating member to elastically vibrate. Through this elastic vibration, the projection of the vibrating member is brought into contact with the moving member, with a certain periodicity. Meanwhile, the force applying means applies a force to the moving member and the projection on the vibrating member to generate a frictional force between the moving member and the vibrating member, thus driving the moving member through the frictional force. 
     Here, it is known that the force applying means includes, in kind, a leaf spring  101  as shown in FIG. 11A or a dish-shaped spring  102  as shown in FIG. 11B, and one formed by a spacer for adjusting the force of the dish-shaped spring (see Japanese Patent Laying-open No H2-287281 and Japanese Patent Laying-open No S63-305770). 
     In the case of the leaf spring  101 , however, there is encountered a variation in force due to a shape of the leaf spring, variation in thickness thereof, variation in thickness of parts such as the vibrating member and the moving member, and variation caused by assembling these parts. Such variation in force in turn causes change in the frictional force between the vibrating member and the moving member and also the drive force to the moving member, thus posing a problem of causing variation in individual characteristics of the ultrasonic motor. 
     On the other hand, where using the dish-shaped spring  102  and the spacer, the force can be adjusted by adjusting the variation in such parts as the dish-shaped spring, vibrating member and moving member, through controlling a spacer thickness. Nevertheless, the force adjustment still requires troublesome operations, such as combining parts due to thickness selection before assembling and disassembling for motor characteristic inspection after assembling, e.g., changing the number of spacers. Furthermore, the adjustment with spacers, even if there is slight difference in thickness, induces greater variation in force applied. Due to this, it is impossible to accurately adjust the force, resulting in such problems as increase in size and decrease in efficiency of the apparatus. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide, in view of the above-stated problems, a small, efficient and stable ultrasonic motor in which prevention is made for variation in force before and after assembling its vibrating member, moving member and so on and adjustment of force is possible without requiring troublesome operations after the assembling, and to provide an electronic apparatus with such an ultrasonic motor. 
     FIG. 1 is a block diagram showing a concept of the present invention. 
     According to the present invention, an ultrasonic motor, has a force applying means  3  for applying a force to a vibrating member  1  to be vibrated as well as to a moving member  2  placed in abutment against the vibrating member  1  to cause a frictional force between them so that the moving member  2  is driven by the frictional force, wherein the force applying means  3  comprises: a main force applying means  3   a  for mainly applying a force; and a force adjusting means  3   b  for adjusting the force applied by the main force applying means  3   a.    
     In the above means, the force applying means  3  includes any of a scheme employing an elastic member, a scheme applying a force by a weight member, and further a scheme applying a force by attraction and repelling due to a magnet or the like. Also, the elastic member includes a spring and rubber, and further the spring includes a leaf spring, a spring with radial arms, a coiled spring, and the like. 
     FIG. 2 is a diagram equivalently representing a principle of the present invention. 
     The force applying means  3  is replaced by a structure having, in parallel connection, the main force applying means  3   a  formed by a spring with a greater elastic constant of K1 and the force adjusting means  3   b  formed by three springs each having a smaller elastic constant of K2, 
     Under a certain constant amount of deflection, the three springs of the force adjusting means  3   b  are connected or cut away to select a total elastic constant from among K1+3K2, K1+2K2, K1+K2 and K1, thereby adjusting the force. 
     According to the present invention, the force adjusting means  3   b  allows the force of the main force applying means  3   a  to be adjusted not only before assembling but also after the assembling. This accordingly prevents variation in the force due to variation in dimension of the vibrating member  1 , the moving member  2  and the force applying means  3 . Also, the vibrating member  1 , the moving member  2  and the force applying means  3  become easy to control on dimensional accuracy. 
     Also, after assembling, the force is adjusted without requiring a disassembly work. Accordingly, an adjustment of the force after assembling becomes easy. 
     Also, after assembling, the force is adjusted with accuracy by connecting or cut away the force adjusting means  3   b . This accordingly realizes a motor that is small in size, high in efficiency and stable. 
     The force applying means may be a leaf spring, and the force adjusting means having slits and strip portions between the slits formed in the leaf spring. 
     According to this structure, the force can adjusted by the slits before assembling, and after the assembling the strip portions between the slits are cut away or connected, thus conducting an adjustment with accuracy. 
     The force applying means may have radially extending arms, the main force applying means being main force applying arm portions which are among the arms and have a predetermined width, and the force adjusting means being force adjusting portion adjusting portions which are among the arms and narrower in width than main force applying arms. 
     According to this structure, the force of the main force applying arms can be adjusted by the force adjusting arms before assembling, and after the assembling part of the force adjusting arms is cut away or bent, thereby conducting an accurate adjustment of the force. 
     The force adjusting means may be worked so as to adjust the force after assembling the vibrating member, the moving member and the force applying means. 
     Here, the working is due to a method of cutting, bending, fusion or the like. 
     This structure allows the force adjusting means to be worked after assembling the vibrating member and the like, enabling accurate adjustment of the force. 
     The force applying means and the moving member may be formed in one body. 
     This structure makes it unnecessary to use a member for providing the force applying means due to making the force applying means and the moving member in one body. This accordingly simplifies the apparatus structure. 
     An electronic apparatus can be provided with the ultrasonic motor. 
     Here, the electronic apparatus includes an electronic timepiece, measuring instrument, camera, printer, printing machine, machine tool, robot, and movable device. 
     This structure can realize an electronic apparatus with a ultrasonic motor to which the present invention is applied. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a concept of the present invention; 
     FIG. 2 is a diagram equivalently representing the principle of the present invention; 
     FIG. 3 is a view showing a sectional structure of a ultrasonic motor according to Embodiment 1 to which the present invention is applied; 
     FIG. 4 shows a plan structure of a force applying spring in FIG. 3, and FIG. 4B is a view showing a plan structure worked after assembling; 
     FIG. 5A shows a plan structure of a force applying spring of a modification to FIG. 4, and FIG. 5B is a view showing a plan structure worked after assembling; 
     FIG. 6 is a view showing a sectional structure of a ultrasonic motor according to Embodiment 2 to which the present invention is applied; 
     FIG. 7 shows a plan structure of a force applying spring in FIG. 6, and FIG. 7B is a view showing a plan structure worked after assembling; 
     FIG. 8 is a view showing a sectional structure of a ultrasonic motor according to Embodiment 3 to which the present invention is applied; 
     FIG. 9A shows a plan structure of a force applying spring in FIG. 8, and FIG. 9B is a view showing a plan structure worked after assembling; 
     FIG. 10 is a block diagram of an electronic apparatus with a ultrasonic motor according to Embodiment 4 to which the present invention is applied; and 
     FIGS. 11A and 11B are explanatory views showing a plan structure of a force applying member of a ultrasonic motor of a conventional art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG.  3  through FIG. 10, explanations will be made hereunder on the present invention in accordance with embodiments thereof. 
     Embodiment 1 
     FIG. 3 illustrates a structure in section of a ultrasonic motor according to Embodiment 1 to which the present invention is applied, while FIG. 4 is a structure in plan of a force applying spring  16  of the ultrasonic motor. 
     The present embodiment is provided with a support plate  11  for supporting the ultrasonic motor, a center shaft  12  having a base end rotatably fixed by the support plate  11 , a vibrating member  13  fixed on an axial center of the center shaft  12 , a piezoelectric element  14  joined to an underside of the vibrating member  13 , a moving member  15  placed in abutment against projections  13   a  of the vibrating member  13 , a force applying spring  16  as a force applying means of the invention that is in pressure contact with the moving member  15 , and a friction plate  17  fixed on the underside of the moving member  15 . 
     Here, the center shaft  12  is a columnar member formed of a rigid material, which fixingly supports the vibrating member  13  and also rotatably supports the moving member  15 . 
     The vibrating member  13  is in a disc form that is formed of an elastic material, such as aluminum alloy, stainless steel and brass. The vibrating member  13  has columnar projections  13   a  provided, at equal intervals, in positions corresponding to divisional boundaries of a piezoelectric element  14  hereinafter referred to. 
     The piezoelectric element  14  is made of titanate zirconate, barium titanate, titanium compound, lithium niobate, lithium tantalate or the like, which is formed in a generally disc form. The piezoelectric element  14  is circumferentially divided into twelve equal fan-like portions so that two sets of polarized portions are provided by making divisional portions positioned every other one as one set polarized portion. The polarization should be made such that the polarized portions of each set are opposite in polarization to each other. Here, as for the direction of polarization, a positive direction was given by applying a positive electric field to a joining plane to the vibrator  13  while a reverse direction is by applying a negative electric field to the joining surface to the vibrating member  13 . 
     The piezoelectric element  14  is formed, at its surface opposite to the joining surface, with electrode patterns by means of evaporation, sputtering, printing, CVD or the like into generally fan-like shapes corresponding to the respective divisional portions. Two sets of electrode patterns are formed by short circuiting between polarized portions of the sets. One electrode pattern is connected to a first lead while the other electrode pattern to a second lead. Meanwhile, the joining surface to the vibrating member  13  is entirely formed with an electrode. Vibration signals different in phase by 90 degrees are inputted respectively to the one electrode pattern and the other electrode pattern so that the polarized portions are vibrated with the phase shifted by 90 degrees thereby causing traveling waves in a circumferential direction of the vibrating member  13 . 
     Note that, in the case of using a standing wave scheme, projections  13   a  are arranged every other one of the divisional portion boundaries, i.e., at respective intermediate points between the node and loop of three wavelengths of standing waves caused in the circumferential direction. When driving in a positive direction, a vibration signal is inputted to the one polarized portion to cause vibration thereby generating three wavelengths of standing waves in the circumferential direction of the vibrating member  13 . Conversely, when driving in a reverse direction, a vibration signal in a same phase is inputted to the other polarized portion to cause vibration thereby generating a standing wave different in phase by  90  degrees in the vibrating member  13 . 
     The moving member  15  is in a disc form using, for example, a rigid material, which has a recess bore  15   a  formed at a center in the underside for receiving the center shaft  12  and a pivot  15   b  formed on the top surface thereof. 
     The force applying spring  16  as a force applying means of the invention is in a leaf spring form using, for example, stainless steel, spring steel or the like, as shown in FIG.  4 A. 
     The force applying spring  16  is formed by a base portion  16   a  for fixation on a not-shown mount member, a force adjusting spring  16   b  as a force adjusting means of the invention formed continuous to the base portion  16   a , and main force applying spring  16   c  as a main force applying means formed continuous to the force adjusting spring  16   b.    
     Here, the base portion  16   a  is rectangular in form to have a circular mount bore  161   a  formed at a center of the rectangular portion. 
     The force adjusting spring  16   b  is formed with straight slits  162   a ,  162   b ,  162   c  extending in a lengthwise direction of the leaf spring, and strip portions  163   a ,  163   b ,  163   c ,  163   d  formed between the slits  162   a ,  162   b ,  162   c.    
     The main force applying spring  16   c  is formed by a main portion  164   a  and a hexagonal portion  164   a  in a hexagon form. 
     The main force applying spring  16   c  is disposed to apply a force to the pivot  15   b  of the moving member  15 . On the other hand, the force adjusting spring  16   b  serves to decrease the rigidity and hence the elastic constant of the force applying spring  16  due to the slits  162   a ,  162   b ,  162   c  to thereby adjust the force of the main force applying spring  16   c.    
     After assembling the entire assembly, the strip portions  163   a ,  163   d  of the force adjusting spring  16   b , for example, are further cut away by a laser cutter to further decrease the elastic constant of the leaf spring and finely adjust the force as shown in FIG.  4 B. 
     The operation of the present embodiment will now be explained with reference to FIGS. 3 and 4. 
     First, vibration signals with phases different by 90 degrees are inputted to the one electrode pattern and the other electrode pattern of the piezoelectric element  14 , to cause the polarized portions to vibrate with a phase difference of 90 degrees. 
     The vibrating member  13  joined to the piezoelectric element  14  is bent to vibrate causing waves traveling in the circumferential direction. The projection  13   a  of the vibrating member  13  undergoes an oval motion, and comes into contact with the moving member  15  during from an origin position to a top position in vertical direction of the oval movement. 
     Meanwhile, the force applying spring  16  is in pressure contact with and applies force to the pivot  15   b  of the moving body  15 . 
     At this time, the main force applying spring  16   c  principally applies a force and is adjusted by the slit portions  162   a ,  162   b ,  162   c  of the force-adjusting spring  16   b . Thus a proper force is applied to the moving member  15 . 
     Due to this force, the moving member  15  is brought into contact with the projection  22   a  being positioned between the origin position and the top position in the oval motion. The moving member  15  is circumferentially applied by a frictional force and rotated in a predetermined direction. 
     In the case that the force is excessively great, the strip portions  163   a ,  163   d  of the force adjusting spring  16   b  may be cut away as shown in FIG.  4 B. 
     At this time, the elastic constant of the force applying spring  16  is decreased by cutting the strip portions  163   a ,  163   d , thus finely adjusting the force. This also eliminates the necessity of dissembling the assembly in an assembled once state. 
     Due to this the moving member  13  is allowed to rotate in a proper r.p.m. range providing a predetermined torque. 
     Note that if the force is excessively decreased by the above working, the strip portions  163   a ,  163   d  may be again connected. 
     Because in the present embodiment the force of the main force applying spring  16   c  is adjusted by the force adjusting spring  16   b  before or after assembling, it is possible to prevent variation in force due to variation in dimension of the vibrating member  13 , moving member  15 , force applying spring  16  and so on. The dimension control becomes easy to control for the vibrating member  13 , moving member  15  and force applying spring  16 . 
     Furthermore, because the adjustment of force is possible without requiring dissembling after assembling the assembly, the adjustment of force after assembling becomes easy to perform. 
     Furthermore, because highly accurate force adjustment is made by cutting away or connecting the strip portions  163   a ,  163   b ,  163   c ,  163   d  of the force adjusting spring  16   b  after assembling, it is possible to realize a motor which is small in size, efficient and stable. 
     FIG. 5 shows a plan structure of a modification of the force applying spring  16  according to the present embodiment. 
     This force applying spring  16  has the force adjusting spring  16   b  formed with slits  165   a ,  165   b ,  165   c ,  165   d ,  165   e  extending in a width direction of the leaf spring to have strip portions  166   a ,  166   b ,  166   c ,  166   d ,  166   e  between the slits  165   a ,  165   b ,  165   c ,  165   d ,  165   e.    
     In this structure, when adjusting the force after assembling the assembly, the force is finely adjusted, for example, by fusing and removing part of the strip portions  166   c  as shown in B in the same figure. 
     Embodiment 2 
     FIG. 6 shows a structure in section of an ultrasonic motor according to Embodiment 2 to which the present embodiment is applied, while FIG. 7 is an illustrative view showing a structure in plan of a force applying spring  23  of the ultrasonic motor. 
     This ultrasonic motor is characterized by providing a center shaft  21  projecting above a moving member  22 , and a force applying spring  23  supported by the center shaft  21  and pressure contacted with a top surface of the moving member  22 , as shown in FIG.  6 . 
     Note that the same structure as that of the Embodiment 1 is denoted by the same reference character to omit explanation. 
     Here, the center shaft  21  is a columnar member formed of a rigid material, and has a flange  21   a  laterally projecting at a top thereof. A force applying spring  23  is supported by this flange  21   a . A moving member  22  is formed at a center portion with a insertion bore  22   a  through which the center shaft  21  is inserted. 
     The force applying spring  23  is formed, as shown in FIG. 7A, by an annular portion  23   b , main force applying arms  23   c ,  23   d ,  23   e ,  23   f  radially extending from an outer edge of the annular portion  23   b , and force adjusting arms  23   g ,  23   h ,  23   i ,  23   j ,  23   k ,  23   l ,  23   m ,  23   n  formed between the main force applying arms  23   c ,  23   d ,  23   e ,  23   f.    
     Specifically, the annular portion  23   b  has at a center an insertion bore  23   a  through which the center shaft  21  is inserted, and a bearing such as a not-shown ball bearing for free rotation with respect to the center shaft  21 . 
     The main force applying arms  23   c ,  23   d ,  23   e ,  23   f  has a predetermined arm width to apply a main force to the moving member  22 . 
     The force adjusting arms  23   g ,  23   h ,  23   i ,  23   j ,  23   k ,  23   l ,  23   m ,  23   n  is formed narrower in arm width than the main force applying arms  23   c ,  23   d ,  23   e ,  23   f , in order to apply a smaller applying force to the moving member  22  than that by the main force applying arms  23   c ,  23   d ,  23   e ,  23   f.    
     The force adjusting arms  23   g ,  23   h ,  23   i ,  23   j ,  23   k ,  23   l ,  23   m ,  23   n  adjust toward increase the applying force of the main force applying arms  23   c ,  23   d ,  23   e ,  23   f  to the moving member  22 . 
     Where the applying force is finely adjusted after assembling the assembly, the force adjusting arms  23   h ,  23   j  are separated from the moving member  22  by fusing or cutting away, as shown in B of the same figure. Also, the force adjusting arms  23   k ,  23   m  are bent upward and separated from the moving member  22 . Accordingly, the force adjusting arms  23   h ,  23   j ,  23   k ,  23   m  do not apply a force to the moving member  22 , thus finely adjusting the total force toward decrease. 
     According to the present embodiment, the force applied by the main force applying arms  23   c ,  23   d ,  23   e ,  23   f  to the moving member  22  is adjusted by the force adjusting arms  23   g ,  23   h ,  23   i ,  23   j ,  23   k ,  23   l ,  23   m ,  23   n . Further, after assembling the assembly, the force adjusting arms  23   h ,  23   j ,  23   k ,  23   m  are formed to be separated from moving member  22  in order to finely adjust the force. Therefore, an effect is obtained similarly to Embodiment 1. 
     Embodiment 3 
     FIG. 8 is a view showing a sectional structure of Embodiment 3 to which the present invention is applied to a ultrasonic motor, while FIG. 9 is a view showing a plan structure of a force applying spring  34  according to the ultrasonic motor. 
     This ultrasonic motor is structured, as shown in FIG. 8, by a center shaft  31  projecting above the moving member  22 , a flange member  32  fixed at an upper portion of the center shaft  31 , a moving member  33  abutted against the projection  13   a  of a vibrating member  13 , and a force applying spring  34  formed integral with the moving member  33  and abutted against an underside of the flange member  32 . Note that the similar structure to that of Embodiment 1 is denoted by the same reference character to omit explanation. 
     Here, the moving member  33  is annular as shown in FIG.  9 A. 
     The force applying spring  34  is formed by an annular ball bearing  34   b  having at a center an insertion bore  34   a  through which the center shaft  31  is inserted, main force applying arms  34   c ,  34   d ,  34   e  radially extending in three directions from an outer edge of the ball bearing  34   b , force adjusting arms  34   f ,  34   g ,  34   h ,  34   i ,  34   j ,  34   k  radially extending between the main force applying arms  34   c ,  34   d ,  34   e.    
     Specifically, the main force applying arms  34   c ,  34   d ,  34   e  have a predetermined arm width to apply a main force to the moving member  33 . 
     Also, the force adjusting arms  34   f ,  34   g ,  34   h ,  34   i ,  34   j ,  34   k  are formed narrower in arm width than the main force applying arms  34   c ,  34   d ,  34   e  in order to apply to the moving member  33  a smaller force than that of the main force applying arms  34   c ,  34   d ,  34   e.    
     The force adjusting arms  34   f ,  34   g ,  34   h ,  34   i ,  34   j ,  34   k  serves to adjust toward increase the applying force of the main force applying arms  34   c ,  34   d ,  34   e  to the moving member  33 , as shown in B of the figure. 
     On the other had, where performing fine adjust of the applying force after assembling the assembly, the force adjusting arms  34   f ,  34   h ,  34   j  are fused or cut away for separation from the moving member  33 . Accordingly, the force adjusting arms  34   f ,  34   h ,  34   j  separated from the moving member  33  do not apply a force to the moving member  33  thus finely adjust the total force toward decrease. 
     According to the present embodiment, the force applied to the moving member  33  by the main force applying arms  34   c ,  34   d ,  34   e  is adjusted by the force adjusting arms  34   f ,  34   g ,  34   h ,  34   i ,  34   j ,  34   k . Further, after assembling the assembly, the force adjusting arms  34   f ,  34   h ,  34   j  are formed to be separated from the moving member  33  in order to finely adjust the force. Therefore, an effect is obtained similar to Embodiment 1. 
     Furthermore, because the number of members for providing the force applying spring is decreased by integrating the moving member  33  and the force applying spring  34 , the assembly is structured simple. 
     Embodiment 4 
     FIG. 10 is a block diagram of an electric apparatus with a ultrasonic motor to which the ultrasonic motor according to the invention is applied. 
     The present apparatus is realized by the provision of a piezoelectric element  41  to be vibrated by a vibration signal, a vibrating member  42  to be elastically vibrated by the vibration of the piezoelectric element  41 , a moving member  43  to be moved by the vibrating member  42 , a force applying means  44  for applying a force to the moving member  43  and the vibrating member  42 , a transmission mechanism  45  to be moved by interacting with the moving member  43 , and an output mechanism  46  to be moved based on the operation of the transmission mechanism  45 . 
     Here, the electronic apparatus with a ultrasonic motor is, for example, an electric timepiece, measuring instrument, camera, printer, printing machine, machine tool, robot, or movable apparatus. 
     The transmission mechanism  45  employs, for example, a transmission wheel such as a gear and frictional wheel. 
     The output mechanism  46  uses, for a camera, a shutter mechanism and lens drive mechanism, for a timepiece, a pointer drive mechanism and calendar drive mechanism, and, for a machine tool, a tool feed mechanism and workpiece feed mechanism. 
     Meanwhile, the moving member  43  may be provided with an output shaft through which torque is delivered so that a power transmission mechanism is provided to realize a drive mechanism by the ultrasonic motor itself without using the transmission mechanism  45  and the output mechanism  46 . 
     According to the present invention, the force of the main force applying means is adjusted before or after assembling. 
     It is therefore possible to prevent variation in force due to variation in the vibrating member, moving member and force applying means and facilitate the control on the dimensional accuracy of the vibrating member, moving member, and the force applying means. 
     Also, the force can be adjusted after assembling the vibrating member and the like without requiring disassembly. This facilitates the after-assembling adjustment of the force. 
     Furthermore, since the force is accurately adjusted after assembling by cutting away or connecting the force adjusting means, a motor is realized which is small in size, highly efficient and stable.