Abstract:
The present invention relates to a PM (Pulse-Width Modulation) type step motor used for conveying an optical pickup lens of media devices or a mobile camera lens. In detail, the present invention relates to a step motor that is composed of a stator, a rotor rotating by interacting with the stator, a lead screw combined with the rotor and rotating with the rotation of the rotor, and a bearing supporting the lead screw and which can perform precise conveying because it can perform fine adjustment and of which the operation state can be precisely sensed by having a position correcting unit that moves the lead screw to a desired position by finely moving it while contracting and stretching and a rotation sensing unit that is disposed at a side of the rotor or a rotary member rotating with the rotor and senses rotation of the rotor.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of Korean Patent Application Nos. 10-2014-0028827, 10-2014-0028829, and 10-2014-0028840, filed on Mar. 12, 2014, which are hereby incorporated by reference in its entirety into this application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a PM (Pulse-Width Modulation) type step motor used for transferring an optical pickup lens or a mobile camera lens of media devices. In detail, the present invention relates to a step motor that is composed of: a stator, a rotor rotating by interacting with the stator, a lead screw combined with the rotor and rotating with the rotation of the rotor, and a bearing supporting the lead screw, which can perform precise transfer because it can perform fine adjustment; and of which the operation state can be precisely sensed by having a position compensator that moves the lead screw to a desired position by finely moving it while contracting and expanding, and a rotation sensing unit which is disposed at a side of the rotor (or a rotary body rotating with the rotor) and senses rotation of the rotor. 
     2. Description of the Related Art 
     In general, PM type small-sized step motors used for transferring an optical pickup lens or a camera lens of media devices are used for parts required to control positions such as precise pick-up of an ODD (Optical Disk Drive) or adjustment of the focus of a camera lens. 
     These step motors can precisely transfer an object, using a lead screw or a gear which has uniform pitches and is disposed at the output side. 
     Further, with increasing technical development, as various devices have been increasingly manufactured with high precision to be small, there is a need for the ability to more precisely transfer those devices. Thus, for this purpose, there is a need for a step motor having higher driving resolution. 
     An ‘apparatus for driving lens of optical pick-up’ has been disclosed in Korean Patent No. 10-0632598 and it uses a method of reducing the pitch of a lead screw in sections requiring high precision. 
     However, it is required to reduce the pitch of a lead screw of a step motor in order to increase resolution for transferring an object, but it is practically difficult to manufacture a lead screw with a pitch of about 0.15 mm or less in mass production due to a mechanical limit in manufacturing. 
     Accordingly, there is a limit in precise transfer of an object only by reducing the pitch of a lead screw of a step motor. 
     Further, since there is no part for precisely sensing the operation of a step motor, there is a limit in improving the transfer resolution for an object to be transferred by the step motor. 
     The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art. 
     DOCUMENTS OF RELATED ART 
     (Patent Document 1) Korean Patent No. 10-0632598 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and the present invention is intended to propose a step motor that is composed of a stator, a rotor rotating by interacting with the stator, a lead screw combined with the rotor and rotating with the rotation of the rotor, and a bearing supporting the lead screw, that can perform precise transfer because it can perform fine adjustment, and of which the operation state can be precisely sensed, by having a position compensator that moves the lead screw to a desired position by finely moving it while contracting and expanding. 
     Further, the present invention provides a step motor of which the operation state can be precisely sensed, by having a rotation sensing unit that is disposed at a side of the rotor or a rotary body rotating with the rotor and senses rotation of the rotor. 
     In order to achieve the above object, according to one aspect of the present invention, there is provided a step motor that includes: stators; a rotor rotating by interacting with the stators; a lead screw combined with the rotor and rotating with rotation of the rotor; and a bearing supporting the lead screw, and that further includes a position compensator moving the lead screw to a desired position by finely changing a position of the lead screw while contracting and expanding. 
     The position compensator may be disposed on a cross-section of the bearing rotatably supporting a first end portion of the lead screw or on a first end of the lead screw. 
     The position compensator may be disposed at any one of the inside or the outside of a bracket supporting the bearing. 
     The step motor may further include a fixing member fixing the position compensator, in which the position compensator is retained outside the bracket by the fixing member. 
     The bracket may be fixed to an assembly structure and the position compensator may be disposed on a side of the assembly structure, so when a position of the assembly structure may be compensated for, the position of the lead screw may be adjusted. 
     The position compensator may include a displacement generating member that is a piezoelectric element and a displacement amplifying member, and the displacement amplifying member may have a fixing portion, a movable portion, and a flat portion. 
     According to another aspect of the present invention, there is provided a step motor that includes: stators; a rotor rotating by interacting with the stators; a lead screw combined with the rotor and rotating with rotation of the rotor; and a bearing supporting the lead screw, and that further includes a rotation sensing unit disposed at a side by the rotor or a rotary member rotating with the rotor and sensing rotation of the rotor. 
     The rotation sensing unit may be disposed at a side by a magnet and may sense rotation of the rotor by sensing rotation of the magnet. 
     The rotation sensing unit may sense rotation of the rotor by sensing a change in magnetic force of the magnet, using a magnetic force sensor that senses a change in magnetic force of the magnet, and the magnetic force sensor may sense one or more of alternation of an N-pole and an S-pole or alternation of N-non-pole or S-non-pole due to rotation of the magnet. 
     The rotation sensing unit may be disposed at a side by a rotary body rotating with the rotor and senses rotation of the rotor by sensing the shape of the rotor, and the rotary body may be a rotating member that is a separate part rotating at the same speed as the rotor. 
     According to a further aspect of the present invention, there is provided a step motor that includes: stators; a rotor rotating by interacting with the stators; a lead screw combined with the rotor and rotating with rotation of the rotor; and a bearing supporting the lead screw, and that further includes: a rotation sensing unit disposed at a side by the rotor or a rotary member rotating with the rotor and sensing rotation of the rotor; and a position compensator moving the lead screw to a desired position by finely changing a position of the lead screw while contracting and expanding. 
     The step motor according to the present invention includes a position compensator moving a lead screw to a desired position by changing the position of the lead screw while contracting and expanding in a step motor that is used for equipment requiring a precise transfer ability such as transfer of an optical pickup lens or a mobile camera lens of media devices, such that it is possible to finely adjust the lead screw at the level of several micrometers. Accordingly, it is possible to achieve precise position compensation and position control at the level of several micrometers required by industrial fields such as the precise optical device field. 
     Further, since the present invention includes a rotation sensing unit disposed at a side by the rotor or a rotary body rotating with the rotor and sensing rotation of the rotor, it is possible to precisely sense the operation state of a motor, and accordingly, it is possible to sense a transfer difference and feeds back compensation of a position for the features of a step motor used in an open loop control type, such that it is possible to perform ultrafine adjustment using the step motor. 
     Further, according to the present invention, when a rotary body of the step motor generates a difference from an actual transfer movement from a required position, it is possible to minimize the difference by precisely sensing the difference and compensating it. 
     Since the present invention includes a position compensator moving the lead screw to a desired position by finely changing a position of the lead screw while contracting and expanding and a rotation sensing unit disposed at a side by the rotor or a rotary member rotating with the rotor and sensing rotation of the rotor, it is possible to precisely sense the operation state of a motor and finely adjust a lead screw at the level of several micrometers, so it is possible to perform precise position compensation using the step motor and achieve position control at the level of several micrometers required by industrial fields such as the precise optical device field. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view of a step motor according to an embodiment of the present invention; 
         FIG. 2  is a perspective view showing the external appearance of the step motor according to an embodiment of the present invention; 
         FIG. 3  is a cross-sectional view of the step motor according to an embodiment of the present invention; 
         FIGS. 4A to 4C  are enlarged views showing end portions of a lead screw of the step motor according to an embodiment of the present invention; 
         FIG. 5  is a view showing in detail a position compensator according to an embodiment of the present invention; 
         FIG. 6  is a view showing the position compensator disposed in an assembly structure; 
         FIG. 7  is a cross-sectional view showing in detail the position compensator in the step motor according to an embodiment of the present invention; 
         FIGS. 8A and 8B  are views illustrating operation of the position compensator in the step motor according to an embodiment of the present invention; 
         FIG. 9  is a view showing the step motor according to an embodiment of the present invention that has been equipped with a rotation sensing unit; 
         FIG. 10A  is a view showing an example in which a magnetic sensor is attached as a magnetic force sensor to a PCB in the present invention and  FIG. 10B  is a view showing an example in which an FG magnetizing pattern is attached as a magnetic force sensor to an FPCB or a PCB in the present invention; 
         FIG. 11A  is a view showing an example in which the rotation sensing unit is disposed on a side of a magnet in the present invention and  FIG. 11B  is a view showing an example in which the rotation sensing unit is disposed on a side of a rotary body in the present invention; and 
         FIGS. 12A to 12D  are views showing various examples of the rotary body in the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A step motor according to the present invention will be described hereafter in detail with reference to the accompanying drawings. 
     A step motor according to the present invention is described with reference to  FIGS. 1 to 3 . 
     The step motor according to the present invention is a common step motor including a lead screw in a motor unit and the detailed configuration is as follows. 
     A step motor according to an embodiment of the present invention may include: a motor unit  10  including stators that are each composed of a bobbin  12  holding a coil generating magnetism when a power is supplied from the outside and a yoke  13  with a plurality of yoke teeth for engaging with the bobbin  12 , cases  14  and  15  that cover and protect the stators, and a magnet  11  that is inserted inside the stator and rotates by interacting with the stators; a lead screw  30  combined with a rotor, converting torque of the rotor into a straight motion, and transmitting the straight motion to the outside; and a bracket  50  for fixing the motor unit. The step motor may further include a rotation sensing unit that senses rotation of the rotor, using a magnetic force. 
     The stators, as shown in  FIG. 1  as an embodiment, are composed of two bobbins  12  holding a coil that generates magnetism when power is supplied from the outside and two yokes  13  combined with the bobbins  12 , respectively, and face each other. Terminals  12   a  are formed at the upper portion of the bobbins  12 . 
     The rotor has a structure in which the magnet  11  magnetized with N-poles and S-poles alternately arranged around the outer side and having a predetermined size is inserted inside the stators and rotates by interacting with the stators and the lead screw  30  has a magnet mount portion  31  inserted and fixed inside the magnet  11  and a threaded portion  32  for converting torque of the rotor into a straight motion. 
     The bracket  50  is formed substantially in a U-shape having a motor unit seat for supporting a side of the motor unit  10 , a horizontal fixing side for fixing the motor unit  10 , and a lead screw support side  51  for supporting a first end portion of the lead screw  30 , and a bearing  71  for rotatably supporting the first end of the lead screw  30  is disposed on the lead screw support side  51 . 
     A center guide  17  supporting a second end portion of the lead screw  30 , a centering member  16  guiding the position of the center guide  17 , and an elastic member  18  axially pushing the center guide  17  are disposed on the second end portion of the lead screw  30 , 
     Instead of the center guide  17 , a bearing (not shown) may be disposed on the second end portion of the lead screw  30  so that both end portions of the lead screw  30  can be rotatably supported by the bearings. 
     A power transmission member (not shown) such as a nut that is combined with an object and moves straight to transfer the object may be disposed on the lead screw  30 , and a position compensator  60  moving the lead screw  30  to a desired position by finely adjusting the position of the lead screw  30  may be further provided. The position compensator  60 , as shown in  FIGS. 2 and 3 , may further has a fixing member  72  that can fix the position compensator  60  outside the lead screw support side  51 , so that the position compensator  60  can be retained outside the bracket  50  by the fixing member  72 . 
     The step motor according to the present invention includes the position compensator  60  that moves the lead screw  30  to a desired position by finely changing the position of the lead screw while contracting and expanding in the structure described above. 
     The position compensator  60  is disposed on the cross-section of the bearing  71  rotatably supporting the first end portion of the lead screw, as shown in  FIG. 3 , or it is disposed on a first end of the lead screw  30 , as shown in  FIG. 4A , and it finely compensates the axial position of the lead screw  30 . 
     At least one of both end portions of the lead screw  30  is inserted through the bearing and rotatably supported, as shown in  FIG. 4A . 
     The position compensator  60 , as shown in  FIGS. 2 and 3 , may be disposed outside the lead screw support side  51  of the bracket  50  that supports the bearing  71 , or it may be disposed inside the lead screw support side  51  of the bracket  50 , as shown in  FIG. 5 . 
     The position compensator  60 , as shown in  FIGS. 2 and 3 , may further has the fixing member  72  that can fix the position compensator  60  outside the lead screw support side  51 , so that the position compensator  60  can be retained outside the bracket  50  by the fixing member  72 . 
     As another example in which the position corrector  60  is disposed outside the lead screw support side  51  of the bracket  50 , as shown in  FIG. 4C , a bracket extension  52  that expands in an inversed L-shape at the end of the lead screw support side  51  of the bracket  50  may be formed instead of the fixing member  72  to support the position compensator  60  with its vertical inner side. 
     As another example of compensating the position of the lead screw  30 , as shown in  FIG. 6 , the bracket  50  may be fixed to an assembly structure S and the position compensator  60  is disposed on a side of the assembly structure S so that the position of the assembly structure S is compensated for by the position compensator  60  and the position of the lead screw  30  is adjusted accordingly. 
     The position compensator  60  is, as shown in  FIG. 7 , composed of a displacement generating member  61  that is a piezoelectric element and displacement amplifying members  62  on and beneath the displacement generating member  61  and the displacement amplifying members  62  are each composed of a fixing portion  62   a , a movable portion  62   b , and a flat portion  62   c . The displacement of the piezoelectric element that is the displacement generating member  61  is very difficult to industrially use, so the displacement amplifying members  62  are specifically provided in the present invention. 
     The position compensator  60  generates displacement by laterally contracting or expanding, as shown in  FIGS. 8A and 8B , when a voltage is supplied to the piezoelectric element that is the displacement generating member  61 . In this case, the piezoelectric element that is the displacement generating member  61  generate longitudinal displacement little, so longitudinal displacement is generated by the displacement amplifying members connected to the piezoelectric element that is the displacement generating member  61 . The piezoelectric element that is the displacement generating member  61  generates displacement proportioned to the intensity of an input voltage, and a voltage to be applied from the outside may be about 60˜100V in the present invention, in which the displacement of the piezoelectric element that is the displacement generating member  61  is about 5˜15 μm. 
     The displacement amplifying members  62  each have the fixing portion  62   a  laterally expanding at a predetermined distance from an end of the displacement generating member  61 , the movable portion  62   b  inclining at an obtuse angle from an end of the fixing portion, and the flat portion  62   c  laterally expanding from an end of the movable portion  62   b , and have two or more bending portions. 
     As the fixing portion  62   a  of the displacement amplifying portion  62  contracts in the same direction as the contraction direction of the displacement generating member  61 , the flat portion  62   c  deforms outward perpendicular to the contraction direction of the fixing portion  62   a  (see  FIG. 8A ), while as the fixing portion  62   a  expands in the same direction as the expansion direction of the displacement generating member  81 , the flat portion  62   c  deforms inward perpendicular to the expansion direction of the fixing portion  62   b  (see  FIG. 8B ). 
     That is, as the displacement generating portion  61  contracts and expands, the flat portion  62   c  axially deforms, so the position of the lead screw  30  can be finely adjusted. 
     The deformation range of the flat portion  62   c  depends on the angle between the fixing portion  62   a  and the movable portion  62   b  and the displacement of the fixing portion  62   a , while the displacement of the fixing portion  62   a  depends on the intensity of a voltage applied to the piezoelectric element that is the displacement generating member  61 . 
     For smooth adjustment of the position of the lead screw  30  by the position compensator  60  in the present invention, as shown in  FIGS. 8A and 8B , the lead screw support side  51  of the bracket  50  and the side of the bearing  71  that rotatably supports the first end portion of the leas screw  30  may be spaced at a predetermined distance t, in which the distance t is made larger than the compensation amount for the position of the lead screw  30  adjusted by the position compensator  60 . 
     On the other hand, the step motor according to the present invention includes a rotation sensing unit  80  that is disposed at a side of the rotor or a rotary body rotating with the rotor in the structure described above and senses rotation of the rotor. 
     As shown in  FIG. 9 , the rotation sensing unit  80  is disposed at a side by the magnet  11  and senses rotation of the rotor by sensing rotate of the magnet  11 . In this configuration, the rotation sensing unit  80  senses a change in magnetic force of the magnet  11 , using a magnetic force sensor  81  that senses a change in magnetic force of the magnet  11 , and analyzes the sensed change in magnetic force of the magnet  11 , thereby sensing rotation of the rotor. 
     The magnetic force sensor  81  senses rotation of the magnet  11  and the rotor by sensing one or more of alternation of an N-pole and an S-pole or alternation of N-non-pole or S-non-pole due to rotation of the magnet  11 . 
     By attaching a magnetic sensor  81  to a PCB, as shown in  FIG. 10A , the magnetic force sensor  81  can sense a change in magnetic force of the magnet  11 . The magnetic force sensor  81  with the magnetic sensor  82  may be given a reinforcing member  83  to be easily combined with a counterpart to be combined with the PCB. For example, when the PCB is 1 mm thick and a counterpart is 4 mm thick, the reinforcing member  83  may be provided to remove gap of 3 mm that is generated in combining. Further, the magnetic sensor  82  may be attached to an FPCB instead of the PCB. 
     The magnetic sensor  82  outputs a sinusoidal voltage by sensing the magnetic force of the magnet  11 , when a voltage is applied from the outside, the output voltage is the maximum when an N-pole or an S-pole of the magnet  11  is positioned at the right center of the magnetic sensor  82 , and the magnetic sensor  82  outputs a sine waveform proportioned to the rotation of the rotor when the motor is operated. A transfer difference of the motor can be sensed when the sine waveform outputted from the magnetic sensor  82  is disconnected and then outputted again, that is, when the sine waveform is not continuous, and it can be compensated for by a module type drive. 
     The magnetic sensor  81  may be achieved by an FPCB or a PCB printed with an FG (Frequency Generator) magnetized pattern, as shown in  FIG. 10B . 
     As another example of the rotation sensing unit  80  in the present invention, as shown in  FIG. 11A , the rotation sensing unit  80  may be disposed at a side by the magnet  11  and sense rotation of the rotor by sensing a change in shape of the rotor or a rotary body rotating with the rotor. The rotary body may be the magnet  11  or the lead screw  30  fitted in the magnet  11 . 
     When the rotary body is the magnet  11 , prominences and depressions may be formed on the portion of the magnet  11  that faces the rotation sensing unit  80 , so that the rotation sensing unit  80  disposed at a side by the magnet  11  can sensing rotation of the rotor by sensing a change of the magnet  11 , when the magnet  11  rotates. 
     As another example of the rotation sensing unit  80  in the present invention, as shown in  FIG. 11B , the rotation sensing unit  80  is disposed at a side by a rotating member  90  that is a separate part as the rotary body rotating with the rotor to sense rotation of the rotor by sensing the shape of the rotary body. The rotating member  90  is a rotary body fitted on the first end portion of the lead screw  30  and rotating at the same speed as the rotor. 
     The rotating member  90  that is a separate part may be formed in various shapes at the portion facing the rotation sensing unit  80  so that the rotation sensing unit  80  can sense a change in shape. 
       FIGS. 12A to 12D  are views showing various embodiments of the rotating member  90 , in which the rotating member  90  may have one or more grooves or protrusions ( FIGS. 12A to 12C ) or one or more holes ( FIG. 12D ). 
     Since the rotation sensing unit  80  is provided, it is possible to precisely sense the operation state of the motor, and accordingly, it is possible to sense a transfer difference and feeds back compensation of a position for the features of a step motor used in an open loop control type, such that it is possible to perform ultrafine adjustment using the step motor. 
     Further, the present invention can include both of a position compensator moving a lead screw to a desired position by finely changing the position of the lead screw while contracting and extending in a step motor and a rotation sensing unit disposed at a side by a rotor or a rotary body rotating with the rotor and precisely sensing rotation of the rotor. 
     Therefore, it is possible to precisely sense the operation state of a motor and finely adjust a lead screw at the level of several micrometers, so it is possible to achieve precise position compensation and position control at the level of several micrometers required by industrial fields such as the precise optical device field. 
     Although the present invention was described above with reference to exemplary embodiments, it should be understood that the present invention may be changed and modified in various ways by those skilled in the art, without departing from the spirit and scope of the present invention described in claims.