Patent Publication Number: US-2007114855-A1

Title: Actuator

Description:
TECHNICAL FIELD  
      The present invention relates to an actuator using a magnetostrictor.  
     BACKGROUND ART  
      An example of the known actuators of this type is the one disclosed in Patent Document 1 below. This actuator has a columnar magnetostrictor, and a drive coil wound on a bobbin around the columnar magnetostrictor. In this case, the columnar magnetostrictor is so arranged that one end face is in contact with a disc magnetic body and that the other end face is in contact with an end face of a magnetic member. In this case, the magnetic member is provided with a flange, and an elastic member is interposed between this flange and a case. Therefore, the magnetic member is biased toward the columnar magnetostrictor by the interposed elastic member, so as to be maintained in a state in which it can freely travel back and forth in the directions along the vibrating directions of the columnar magnetostrictor. In consequence, the disc magnetic body, the columnar magnetostrictor, and the magnetic member are integrally coupled so as to permit vibration of the columnar magnetostrictor.  
      In this actuator, when a drive current based on an input signal is supplied, the drive coil generates a magnetic field oriented along the axial direction of the columnar magnetostrictor. On this occasion, the columnar magnetostrictor expands and contracts in the axial direction of the columnar magnetostrictor as the generated magnetic field is applied thereto. For this reason, the magnetic member vibrates in the axial direction of the columnar magnetostrictor in accordance with the expansion and contraction of the columnar magnetostrictor. Therefore, when this magnetic member is urged against a vibrator such as a diaphram, the vibration of the magnetic member is transmitted to the vibrator.  
      Patent Document 1: Japanese Patent Application Laid-Open Gazette No. 9-261797 (page 3, FIG. 1)  
     DISCLOSURE OF THE INVENTION  
     Problem to be Solved by the Invention  
      However, this actuator has the following problem. Namely, in this actuator the columnar magnetostrictor is made of a material that can break (crack). In addition, the columnar magnetostrictor has such a property that with application of a magnetic field along the axial direction, displacement with expansion and contraction in the part near the edge of the end face of the columnar magnetostrictor is greater than displacement with expansion and contraction in the central part. Therefore, even if the columnar magnetostrictor is formed with flat end faces at the both ends thereof, the two end faces are deformed into such a conical shape that the central part has an invisibly small depression, upon expansion of the columnar magnetostrictor with application of the magnetic field. On this occasion, the columnar magnetostrictor comes into contact only in the edge of the end faces of the columnar magnetostrictor with each end face of the disc magnetic body and the magnetic member. Therefore, the stress due to the expansion of the columnar magnetostrictor is concentrated at the edge of the end faces of the columnar magnetostrictor. In consequence, this actuator has a risk that the edge of the end faces can crack and break because of repetitions of the stress concentration after long-term use. If a foreign body such as dust is attached to an end face of the columnar magnetostrictor, the stress due to expansion of the columnar magnetostrictor could also be concentrated on the part to which the foreign body is attached, so as to break the columnar magnetostrictor. Furthermore, the columnar magnetostrictor could also break with application of an external force due to a drop or the like to an end face. Moreover, there is fine unevenness in the end faces of the columnar magnetostrictor and the stress is likely to be concentrated on this unevenness, in the same manner as the stress is concentrated on the part where the foreign body is attached, so as to be one of the causes of breakage.  
      The present invention has been accomplished in view of the problem to be solved and a principal object of the invention is to provide an actuator capable of avoiding the breakage of the columnar magnetostrictor.  
     Means for Solving the Problem  
      In order to achieve the above object, an actuator according to the present invention comprises a columnar magnetostrictor one end of which is defined as a fixed end and an other end of which is defined as a free end to expand and contract along an axial direction; a magnetic field generator for generating a magnetic field to expand and contract the columnar magnetostrictor by a drive current; and an elastic member disposed on at least one end face of the columnar magnetostrictor, the actuator being arranged to be able to actuate an object with expansion and contraction of the columnar magnetostrictor.  
      In this case, preferably, the elastic member is disposed on each of two end faces of the columnar magnetostrictor.  
     EFFECT OF THE INVENTION  
      In the actuator according to the present invention, the elastic member is disposed on at least one end face of the columnar magnetostrictor, whereby the elastic member absorbs stress applied to the end face of the columnar magnetostrictor. With this actuator, therefore, it is feasible to avoid occurrence of breakage of the columnar magnetostrictor due to the concentration of stress on the edge of the end face of the columnar magnetostrictor, the concentration of stress on the end face of the columnar magnetostrictor due to attachment of a foreign body, and the concentration of an external force on the end face due to a drop or the like. Even if breakage occurs, the degree of the breakage can be reduced.  
      In the actuator according to the present invention, the elastic member is disposed on each of the two end faces of the columnar magnetostrictor, whereby it is feasible to more effectively avoid the breakage of the columnar magnetostrictor due to the stress and external force on the columnar magnetostrictor. Even if breakage occurs, the degree of the breakage can be further reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a sectional view showing a configuration of pencil type speaker  1 .  
       FIG. 2  is a block diagram showing an electric circuit of pencil type speaker  1 .  
    
    
     DESCRIPTION OF REFERENCE SYMBOLS  
       1 : pencil type speaker;  22 : partition;  51 : columnar magnetostrictor;  54 : drive coil;  55 : vibration transmitter;  52   a,    52   b:  sponges.  
     BEST MODES FOR CARRYING OUT THE INVENTION  
      The best mode of the actuator according to the present invention will be described below with reference to the accompanying drawings.  
      First, a configuration of pencil type speaker  1  to which the actuator according to the present invention is applied, will be described with reference to the drawings.  
      The pencil type speaker  1 , as shown in  FIG. 1 , has a cylindrical housing  2 , an acoustic signal amplifier  3 , a power supply  4 , and a vibration transducer  5 , and is arranged to be able to output an acoustic signal when the tip of the pencil type speaker  1  is urged, for example, against a plate  7  as a vibrator. The housing  2 , as shown in the same figure, is constructed with an upper housing body  2   a  and a lower housing body  2   b  each made of synthetic resin, and the two housing bodies  2   a,    2   b  are integrally coupled through engagement between engaging parts formed at end portions thereof, thereby forming an elongated pencil shape as a whole. The upper housing body  2   a  is provided with a partition  21 , the acoustic signal amplifier  3  is housed in an interior space on the rear end side partitioned by this partition  21 , and the power supply  4  is housed in an interior space on the tip end side partitioned by the partition  21 . On the other hand, another partition  22  for separating the power supply  4  from the vibration transducer  5  is fixed to the lower housing body  2   b.    
      The acoustic signal amplifier  3 , as shown in  FIG. 2 , amplifies an acoustic signal fed through an acoustic signal cable  6  from the outside and outputs a drive current generated, through an unrepresented connection cable to a drive coil  54 . The acoustic signal amplifier  3 , as shown in  FIG. 1 , is provided with an amplifier substrate  31  disposed on the rear end side of the upper housing body  2   a,  and a power switch  32  and an acoustic signal input connector  33  are mounted, as shown in the same figure, on this amplifier substrate  31 . In this case, the power switch  32 , as shown in the same figure, is provided with a knob  34  permitting a user to turn on and off the pencil type speaker  1  through switching operation. The acoustic signal input connector  33 , as shown in the same figure, is constructed as a jack into which a plug  61  of the acoustic signal cable  6  for input of the acoustic signal from the outside can be inserted.  
      The power supply  4 , as shown in  FIGS. 1 and 2 , is constructed as an example with three dry batteries  41 ,  41 ,  41 , a battery terminal  42  fixed to the partition  21 , and a battery terminal  43  fixed to the partition  22 , and supplies power to the acoustic signal amplifier  3  through connection cables connected to the battery terminals  42 ,  43 . In this case, the dry batteries  41  are taken in and out through an opening at the distal end of the upper housing body  2   a  in a state in which the upper housing body  2   a  is separated from the lower housing body  2   b  as the engaging parts are disengaged from each other.  
      The vibration transducer  5  is disposed in the interior space of the lower housing body  2   b  and, as shown in  FIGS. 1 and 2 , is constructed with a columnar magnetostrictor  51 , sponges  52   a,    52   b,  bias magnets  53   a,    53   b,  a drive coil  54 , a vibration transmitter  55 , and, for example, four springs  56 . The columnar magnetostrictor  51  functions as an element that expands and contracts in the axial direction with application of a magnetic field in a direction along the axial direction, to convert a variation of the magnetic field into mechanical vibration. The columnar magnetostrictor  51  is made, for example, of a giant magnetostrictive material having the central composition of Th0.34-Dy0.66-Fe1.90, which produces a large displacement of approximately not less than 1500 ppm nor more than 2000 ppm in the axial direction in a magnetic field. One end of the columnar magnetostrictor  51  on the partition  22  side corresponds to the fixed end in the present invention, and the other end on the vibration transmitter  55  side corresponds to the free end in the present invention.  
      The sponges  52   a,    52   b  correspond to the elastic member in the present invention and function as elastic bodies before application of a predetermined pressure. On the other hand, when an external force over the predetermined pressure is applied, the sponges  52   a,    52   b  seldom function as elastic bodies, but they function as inelastic plate bodies that transmit vibration and that have such hardness as to absorb stress concentrated on the end faces. In this case, the sponge  52   a  is disposed in a state in which one end face of the sponge  52   a  is in contact with the end face of the columnar magnetostrictor  51  on the upper housing body  2   a  side (corresponding to one end face of the columnar magnetostrictor in the present invention) and in which the other end face of the sponge  52   a  can come into contact with the bias magnet  53   a.  The sponge  52   b  is disposed in a state in which one end face of the sponge  52   b  is in contact with the end face of the columnar magnetostrictor  51  on the vibration transmitter  55  side (corresponding to one end face of the columnar magnetostrictor in the present invention) and in which the other end face of the sponge  52   b  can come into contact with the bias magnet  53   b.    
      The bias magnet  53   a,  as described above, is disposed between the sponge  52   a  and the partition  22  in a state in which it can come into contact with the other end face of the sponge  52   a,  and the bias magnet  53   b  is disposed between the sponge  52   b  and after-described flange  55   a  in a state in which it can come into contact with the other end face of the sponge  52   b.  In this case, the bias magnets  53   a,    53   b  apply such a bias magnetic field as to be able to move the columnar magnetostrictor  51  between operating points to effect approximately linear expansion and contraction (vibration) against variation of the magnetic field in the axial direction. Therefore, the columnar magnetostrictor  51  expands to a length corresponding to the operating point to effect approximately linear expansion and contraction with application of the bias magnetic field. The drive coil  54  corresponds to the magnetic field generator in the present invention and, as shown in  FIGS. 1 and 2 , is disposed so that the center axis of the drive coil  54  becomes coaxial with the center axis of the columnar magnetostrictor  51 . The drive coil  54 , as shown in  FIG. 2 , generates the magnetic field on the axis of the drive coil  54  (or on the axis of the columnar magnetostrictor  51 ) with input of the drive current from the acoustic signal amplifier  3  through the connection cable.  
      The vibration transmitter  55 , as shown in  FIG. 1 , is integrally constructed with the flange  55   a  of disc shape, shaft  55   b,  and tip contact part  55   c.  The flange  55   a,  as shown in the same figure, is in contact at the upper end face of the flange  55   a  with the sponge  53   b  and in contact at the lower end face of the flange  55   a  with the springs  56 . Each spring  56 , as shown in the same figure, is disposed in the interior space of the lower housing body  2   b  in a state in which one end thereof is in contact with the flange  55   a  while the other end is in contact with the inner wall of the lower housing body  2   b  and in which it biases the flange  55   a  toward the columnar magnetostrictor  51 . The shaft  55   b  is so arranged that the tip contact part  55   c  is fixed to the distal end face of the shaft  55   b,  and transmits vibration of flange  55   a  to the tip contact part  55   c.  The tip contact part  55   c,  as shown in the same figure, has the tip end formed in a semispherical shape, as an example, and transmits vibration of the vibration transmitter  55  to the plate body  7  when urged against the plate body  7  (the object in the present invention). As shown in the same figure, therefore, the springs  56  bias the flange  55   a  so as to integrally couple the flange  55   a,  bias magnet  53   b,  sponge  52   b,  columnar magnetostrictor  51 , sponge  52   a,  and bias magnet  53   a  and so as to maintain the vibration transmitter  55  in a state in which it can travel back and forth (or can vibrate) along the axial direction of the vibration transmitter  55 . In consequence, the vibration transmitter  55  moves away from the partition  22  with expansion of the columnar magnetostrictor  51 , and moves toward the partition  22  with contraction of the columnar magnetostrictor  51 . As a result, the vibration transmitter  55  (flange  55   a ) vibrates in the directions along the directions of expansion and contraction of the columnar magnetostrictor  51  in accordance with the expansion and contraction of the columnar magnetostrictor  51 .  
      Next, the overall operation of the pencil type speaker  1  will be described.  
      In this pencil type speaker  1 , the acoustic signal amplifier  3  amplifies an acoustic signal fed through the acoustic signal cable  6  from the outside and supplies the drive current to the drive coil  54 . On this occasion, the drive coil  54  applies the magnetic field generated based on the supplied drive current, to the columnar magnetostrictor  51 . For this reason, the columnar magnetostrictor  51  expands and contracts in the axial direction according to the applied magnetic field. On this occasion, when the tip contact part  55   c  is urged against the plate body  7  under such predetermined pressure as to contract the sponges  52   a,    52   b  over the limit for retention of elasticity thereof, the partition  22  functions as a stopper (i.e., inertia mass together with the weights of a human hand and pencil type speaker  1 ), whereby the sponges  52   a,    52   b  become compressed to function as inelastic plate bodies. Therefore, the vibration with expansion and contraction of the columnar magnetostrictor  51  is transmitted through the sponge  52   b,  the bias magnet  53   b,  the flange  55   a,  the shaft  55   b,  and the tip contact part  55   c  to the plate body  7  during this period. In this state, with vibration of the plate body  7 , the acoustic signal fed from the outside is outputted as adequately audible sound from the plate body  7 .  
      In the pencil type speaker  1 , with application of the bias magnetic field by the bias magnets  53   a,    53   b,  the columnar magnetostrictor  51  is expanded (displaced) to the length to enable approximately linear expansion and contraction. In this case, the columnar magnetostrictor  51  demonstrates greater displacement in the region near the edge of the end faces of the columnar magnetostrictor  51  than displacement in the central part, and thus the end faces of the columnar magnetostrictor  51  are deformed in the conical shape. In this state, when the magnetic field generated based on the drive current is applied to the columnar magnetostrictor  51 , the columnar magnetostrictor  51  expands and contracts in the axial direction according to the magnetic field applied. In this case, the end faces of the columnar magnetostrictor  51  are deformed in a deeper conical shape with forward increase in the strength of the applied magnetic field, and deformed in a shallower conical shape with backward increase in the strength of the applied magnetic field. Therefore, the end faces of the columnar magnetostrictor  51  always maintain the conical shape though the depth thereof varies. In consequence, if the columnar magnetostrictor  51  were so arranged that hard and flat members are in contact with the two end faces of the columnar magnetostrictor  51 , almost the entire stress due to the expansion of the columnar magnetostrictor  51  must be concentrated on the edge of the end faces of the columnar magnetostrictor  51 . On the other hand, in the case of this pencil type speaker  1 , the sponges  52   a,    52   b  disposed on the two end faces of the columnar magnetostrictor  51  sufficiently absorb the stress concentrated on the edge in the two end faces of the columnar magnetostrictor  51 . With this pencil type speaker  1 , therefore, it is feasible to avoid occurrence of breakage of the columnar magnetostrictor  51  due to the concentration of stress on the edge of the end faces of the columnar magnetostrictor  51 . Even if breakage occurs, the degree of the breakage can be reduced.  
      If a foreign body such as dust is attached to an end face of the columnar magnetostrictor  51 , the stress due to expansion of the columnar magnetostrictor  51  will be concentrated on the part where the foreign body is attached and on fine unevenness in the end face. In this pencil type speaker  1  on the other hand, the sponges  52   a,    52   b  disposed on the two end faces of the columnar magnetostrictor  51  absorb the stress concentrated on the part where the foreign body is attached and on the fine unevenness in the end face. Therefore, it is feasible to avoid occurrence of breakage of the columnar magnetostrictor  51  due to attachment of the foreign body and the presence of fine unevenness in the end face. Even if breakage occurs, the degree of the breakage can be reduced.  
      If an external force due to a drop or the like is applied to the tip contact part  55   c,  the external force can be concentrated on the end faces of the columnar magnetostrictor  51  to break the columnar magnetostrictor  51 . In the pencil type speaker  1 , however, the sponges  52   a,    52   b  disposed on the two end faces of the columnar magnetostrictor  51  absorb the external force. Therefore, it is feasible to avoid occurrence of breakage of the columnar magnetostrictor  51  due to a drop or the like. Even if breakage occurs, the degree of the breakage can be reduced.  
      The present invention is by no means limited to the above-described configuration. For example, the above configuration described the configuration with two sponges  52   a,    52   b,  but it is also possible to adopt a configuration with only one of the sponges  52   a,    52   b.  By this configuration, it is also feasible to avoid breakage of the columnar magnetostrictor  51  due to the concentration of stress and external force. Even if breakage occurs, the degree of the breakage can be reduced.  
      The above described the configuration with the bias magnets  53   a,    53   b,  but it is also possible to adopt a configuration in which at least one of the sponges  52   a,    52   b  is disposed so as to be able to contact at least one end face of the columnar magnetostrictor  51 , without provision of the bias magnets  53   a,    53   b.  By this configuration, it is also feasible to avoid breakage of the columnar magnetostrictor  51  due to the concentration of stress and external force. Even if breakage occurs, the degree of the breakage can be reduced.  
      The above described the configuration employing the sponges  52   a,    52   b  as the elastic member according to the present invention, but it is also possible to adopt a configuration using rubber or the like, instead of the sponges. By this configuration, it is also feasible to avoid the breakage of the columnar magnetostrictor  51  due to the concentration of stress and external force on the columnar magnetostrictor  51 . Even if breakage occurs, the degree of the breakage can be reduced.  
      The above described the pencil type speaker  1  in the configuration with one columnar magnetostrictor  51 , but the number of columnar magnetostrictor  51  is not limited to  1 , and may be two or more. It is a matter of course that in this configuration a bias magnet and sponge may be optionally disposed between columnar magnetostrictors  51 .  
      Furthermore, the above described the example of application of the actuator according to the present invention to the pencil type speaker  1 , but it is commonly and generally applicable to actuators for actuating an object, without having to be limited to the application to the acoustic equipment such as the pencil type speaker.