JP2011151921A - Linear actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a linear actuator that suppresses a sliding resistance between a rotor and a member for supporting the rotor and reduces the manufacturing cost by reducing a component such as a bearing and improving the processability of components or the like. <P>SOLUTION: The linear actuator 1 is configured to include a motor 10 as a drive source and a linear conversion mechanism for converting a rotative power of the motor 10 into a linear power to transmit the linear power to a driven body respectively in a case 52. The linear conversion mechanism has a lead screw 18 rotated by a rotor 14 of the motor 10, a carriage 20 screwed to the lead screw 18 and linked with the driven body, rotation preventing members 30, 40 for preventing the rotation of the carriage 20. The rotor 14 and the lead screw 18 are integrally formed and freely rotatably supported by a fixed shaft 16 fixed to the case 52. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a linear actuator, and more particularly to a linear actuator that includes a mechanism that converts rotational power of a motor into linear power and moves a driven body forward and backward in the axial direction of the motor.

  Conventionally, a linear actuator that moves a driven body forward and backward based on rotational power of a motor (stepping motor) is generally known. Such a linear actuator is suitably used as a drive device for a valve body that opens and closes flow paths of various gases and liquids. For example, a gas heater such as a gas water heater can be used as a fuel gas open / close valve or a gas flow rate adjustment valve. It is often used for combustion equipment.

  As this type of linear actuator, for example, Patent Document 1 describes a motor that is a drive source and a linear actuator that has a rotating shaft that is provided integrally with a rotor of the motor. A lead screw is formed on the rotating shaft, and a carriage whose movement in the rotational direction is restricted is screwed to the lead screw. The carriage is connected to the driven body. With this configuration, when the motor rotates, the driven body moves linearly with the carriage whose rotation is restricted. That is, the rotational power of the motor is converted into linear power and output to the driven body.

JP 2005-172154 A

  However, the configuration of Patent Document 1 in which a rotating shaft that rotates integrally with the rotor and a lead screw is formed on the rotating shaft has the following problems.

  The first problem is that since the shaft that supports the rotor rotates, it is necessary to employ a configuration in which a bearing is separately provided or the rotating shaft is supported by the case. That is, since a bearing that supports the rotating shaft is required, the cost of components increases, which is a problem. In addition, if the configuration is such that one end of the rotating shaft is supported by the case as in the configuration of Patent Document 1, it is not necessary to provide a separate bearing for that part, but this configuration can rotate the rotating shaft with the case ( Generally, it is a press-processed product and is supported by a bearing portion whose dimensional accuracy is not so high), the sliding resistance between the rotating shaft and the case is increased. Such an increase in sliding resistance between the rotating body and a member that supports the rotating body causes various problems such as an increase in energy loss and a reduction in device life due to severe wear of the member.

  The second problem is that a lead screw is formed on the rotating shaft that supports the rotation of the rotor. In other words, the rotating shaft that supports the rotation of the rotor needs to be formed of a material having sufficient mechanical strength (for example, stainless steel). However, the formation of the lead screw with respect to the material having such strength is difficult to process, so that the processing cost increases.

  In view of the above situation, the problem to be solved by the present invention is to suppress the sliding resistance between the rotating body and the member supporting it, and to reduce the manufacturing cost by reducing the number of parts such as bearings and improving the workability of the parts. It is to provide a linear actuator.

  Based on the above problems, the inventors of the present application have considered the following linear actuator configuration. In other words, the shaft that supports the rotor itself is a fixed shaft that does not rotate, and the rotor and the lead screw are configured separately, and these are rotatably supported by the fixed shaft, and when the rotor rotates, the rotational power is transferred to the lead screw. A configuration to be transmitted (a configuration according to a later-described study example 1 (comparative examples)) was considered. The structure in which the rotor and the lead screw are separately supported by the fixed shaft is as follows: 1) A through hole through which the fixed shaft is inserted can be easily formed, and 2) a lead formed of a metal material. Minimize the size of the screw and minimize the amount of expensive metal materials used. 3) Form the rotor and lead screw separately and make them expandable to other products (common parts), etc. For.

  With this configuration, it is not necessary to use a bearing that supports the rotating shaft, and it is not necessary to support the rotating shaft with a case. Moreover, there is no problem that the workability of the lead screw is poor.

  However, when such a configuration is adopted, a new problem has arisen that noise during driving of the actuator is large. As a result of intensive research by the inventors, the noise is caused by rotating the lead screw in the direction in which the carriage (driven body) is pulled in (the direction in which it is moved downward) by the motor, and the lower limit is reached (the carriage can be lowered further). It has been found that this is caused by the collision between the rotor and the lead screw when the carriage is lowered to a state where the motor is out of step.

  The present invention has been made based on such knowledge, and in a case, a motor as a drive source and a linear motion conversion mechanism that converts the rotational power of the motor into linear power and transmits it to the driven body. In the linear actuator provided, the linear motion conversion mechanism includes a lead screw rotated by a rotor of the motor, a carriage screwed into the lead screw and linked to the driven body, and a rotation for preventing the carriage from rotating. The gist of the invention is that the rotor and the lead screw are integrally formed and are rotatably supported by a fixed shaft fixed to the case.

  According to the linear actuator of the present invention, since the shaft that supports the rotation of the rotor is a fixed shaft that does not rotate, the sliding resistance between the rotating body and the member that supports the same as in the conventional linear actuator There is no problem of generation of energy loss or reduction in device life. Further, there is no need to provide a bearing that supports the rotating shaft. Furthermore, since it is not the structure which forms a lead screw in the axis | shaft which supports rotation of a rotor, a lead screw can be formed with a soft metal material like brass, for example, and the workability of a lead screw improves.

  Moreover, since the rotor and the lead screw that are rotatably supported by the fixed shaft are integrally formed, the collision between the rotor and the lead screw that occurs when the carriage is pulled to the lower limit and the motor is out of step. It is possible to prevent noise from being generated.

  In this case, the rotor and the lead screw can be formed of different materials. As a preferred example, there may be mentioned a configuration in which the rotor is formed of a resin and the lead screw is formed of a metal material.

  The rotor and the lead screw can be integrated by insert molding or fixing with an adhesive. Therefore, both can be formed of different materials. If the rotor is made of a light resin material, the energy loss of the motor can be reduced. The lead screw screwed with the carriage connected to the driven body is made of a metal material, so that the necessary strength can be ensured while reducing the thickness thereof.

  Further, in the case where the lead screw is integrally formed with the rotor by insert molding, the lead screw includes at least a part embedded in the rotor and an end surface on one side of the support part. A through hole through which the fixed shaft is inserted, and at least a peripheral portion of the through hole on the other end surface of the support portion is exposed to the outside. It only has to be. For example, when the support portion is formed in a cylindrical shape and the exposed portion on the other end surface of the support portion is formed in a circular shape, the length from the outer edge of the exposed portion to the outer edge of the through hole It is preferable that the length is ½ or more of the length from the outer edge of the support portion to the outer edge of the through hole.

  As described above, when the peripheral portion of the through hole on the other end face of the support portion is exposed, when the rotor and the lead screw are integrated by insert molding, the mold contacts the peripheral portion of the through hole. Therefore, the molten resin is prevented from flowing into the through hole through which the fixed shaft is inserted. In order to surely prevent the molten resin from flowing in, to increase the contact area between the insert mold and the support, the size of the exposed portion should be set so that the above relationship is established. Good.

  In this case, a concave portion is formed on the bottom surface of the rotor, and the exposed portion of the other end surface of the support portion is a bottom surface, and a sliding portion protruding in the axial direction of the fixed shaft is formed on the opening periphery of the concave portion. It only has to be formed.

  In this way, the concave portion is formed so that the exposed portion becomes the bottom surface, that is, the end surface on the other side of the support portion does not protrude outward from the rotor, and the sliding portion is formed on the opening periphery of the concave portion. If formed, the sliding portion (sliding area with the case) of the rotating rotor becomes small, so that energy loss due to sliding resistance can be kept small.

  According to the linear actuator according to the present invention, the generation of noise due to the collision between the rotor and the lead screw is prevented, the sliding resistance is reduced by the rotation of the rotating body, the number of parts constituting the device is reduced, the lead screw, etc. Easy part processing can be achieved.

It is sectional drawing of the linear actuator concerning one Embodiment of this invention. It is a disassembled perspective view of the linear actuator concerning one Embodiment of this invention. It is the schematic of an insert molding die in the case of integrating a lead screw with a rotor by insert molding. It is the front view which looked at the linear actuator shown in FIG. 1 and FIG. 2 from upper direction. It is the schematic which showed the structure of the linear actuator concerning each examination example. It is the schematic for demonstrating the noise generation | occurrence | production mechanism in the linear actuator which has the structure by which the rotor and the lead screw were each supported by the fixed shaft separately. It is a measurement result of the frequency characteristic in the audible range of the sound generated from the linear actuator according to the example. It is a measurement result of the frequency characteristic in the audible range of the sound generated from the linear actuator according to Comparative Example 1. It is a measurement result of the frequency characteristic in the audible range of the sound generated from the linear actuator according to Comparative Example 2.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of a linear actuator 1 according to an embodiment of the present invention, and FIG. 2 is an exploded perspective view thereof (excluding a stator 12). In the following description, the vertical direction refers to the vertical direction in FIG.

  The linear actuator 1 according to this embodiment is used as a valve body driving device that opens and closes a flow path of a gas pipe provided in a gas combustion device such as a gas water heater. As shown in FIG. 1, the linear actuator 1 is attached to a sealed space 90 such as a gas pipe via a packing 92 or the like. That is, the sealed space 90 is sealed by the linear actuator 1 itself so that the passing gas does not leak.

  The linear actuator 1 includes a motor 10 as a drive source in a case (in the main body case 52 and the stator case 50), and a valve body (not shown) that converts rotational power of the motor 10 into linear power. A linear motion conversion mechanism for transmitting to

  The motor 10 is a known stepping motor and includes a stator 12 and a rotor 14. The stator 12 is configured by winding a drive coil 122 around a stator core 121, and is housed in a stator case 50 that is attached to the outside of the main body case 52. The rotor 14 has a permanent magnet 142 fixed to a resin holder 143. In the present application, the material of the rotor 14 refers to the material (that is, resin) of the holder 143 excluding the permanent magnet 142. A through hole 143a is provided at the center of the holder 143, and a lead screw 18 described later is fixed to the through hole 143a.

  The linear motion conversion mechanism includes a lead screw 18, a carriage 20 screwed into the lead screw 18, a first rotation prevention member 30 and a second rotation prevention member 40 (both of which are the main parts). Corresponding to the rotation preventing member according to the invention.

  The lead screw 18 is a member having a support portion 181 and a screw portion 182 and having a through hole 18a formed at the center. Since the through-hole 18a is formed in the center, the material is preferably a metal so that sufficient strength can be ensured even if the wall thickness is reduced. In consideration of workability, brass is preferable. As can be seen from FIG. 2, the support portion 181 is a cylindrical portion. The screw portion 182 is a portion in which a male screw (screw) having a predetermined diameter and pitch is formed on a shaft that is erected vertically from one end (tip side) end surface of the support portion 181.

  In the present embodiment, the lead screw 18 having such a configuration is integrated with the rotor 14 by insert molding. Examples of other integration methods include press-fitting and fixing to a through hole 143a formed in the holder 143, and integration using an adhesive (or a combination thereof). Thus, in this embodiment, since the rotor 14 and the lead screw 18 may be integrated by insert molding or fixing with an adhesive, the two can be molded from different materials. Specifically, the lead screw 18 that needs a sufficient strength while being thin is molded from a metal material, and the holder 143 of the rotor 14 that needs to be lightweight is molded from a resin material. It can be suitably selected according to the required characteristics.

  The integrated rotor 14 and lead screw 18 are rotatably supported by a fixed shaft 16 (the fixed shaft 16 itself does not rotate) inserted through the through hole 18 a of the lead screw 18. In addition, the through-hole 18a is a very long thing formed from the support part 181 to the screw part 182, and a process is difficult (a drill (bite | tool) may be broken at the time of a cutting process). Therefore, in the present embodiment, as described later, the diameter of the through hole 18a formed in the support portion 181 embedded in the rotor 14 (holder 143) is reduced (for example, 1.2 mm), and the rotor 14 (holder 143). The diameter of the through hole 18a formed in the screw portion 182 protruding from the diameter is increased (eg, 1.3 mm). By doing in this way, the through-hole 18a can be formed in two steps, and processing becomes easy. The reduction in the diameter of the through hole 18a formed in the support portion 181 embedded in the rotor 14 (holder 143) is generated from the stator 12 by reducing the clearance between the fixed shaft 16 and the through hole 18a in that portion. This is to prevent the rotating rotor 14 from rattling by the magnetic field.

  The linear actuator 1 according to the present embodiment is a linear actuator in which the rotor 14 and the lead screw 18 are separately rotatably supported on the fixed shaft 16 (corresponding to Study Example 1 and Comparative Examples described later). After elucidating the mechanism of noise generation, the rotor 14 and the lead screw 18 are integrated to reduce noise during driving of the actuator.

  A thrust bearing (washer) 17 made of resin (polyethylene terephthalate) is interposed between the lower surface of the rotor 14 (holder 143) rotatably supported by the fixed shaft 16 and the main body case 52. This is to reduce the sliding resistance between the rotating rotor 14 and the main body case 52.

  When the rotor 14 and the lead screw 18 are integrated by insert molding, the linear actuator 1 further has a configuration for reducing the sliding resistance between the rotor 14 and the main body case 52. Specifically, the bottom surface 144 of the rotor 14 (holder 143) is formed with a sliding portion 15 protruding in an annular shape.

  The reason why such a sliding portion 15 is formed on the rotor 14 (holder 143) is as follows. For example, the bottom surface 18b of the lead screw 18 (the end surface opposite to the end surface of the support portion 181 from which the screw portion 182 protrudes (the other end)) is protruded from the bottom surface 144 of the holder 143. When the rotation is supported, the sliding loss increases due to the surface contact between the inner bottom surface of the main body case 52 and the bottom surface 18b of the lead screw 18, which causes a problem. On the other hand, the lead screw 18 may be formed with a protruding portion (annular protruding portion such as the sliding portion 15) protruding from the bottom surface 18b so as to be in line contact with the inner bottom surface of the main body case 52. Forming such a protrusion on the bottom surface 18b of the lead screw 18 made of metal is problematic because workability is reduced. That is, a configuration in which the rotation of the rotor 14 is supported by the lead screw 18 is not appropriate.

  Therefore, the lead screw 18 is integrated with the holder 143 so that the bottom surface 18 b does not protrude outside the holder 143. In addition, the peripheral portion of the through hole 18a in the bottom surface 18b of the lead screw 18 (the portion having the radial dimension L1) is exposed to the outside (hereinafter, this portion may be simply referred to as an exposed portion). . The reason why the peripheral portion of the through hole 18a is exposed is to prevent the molten resin from flowing into the through hole 18a of the lead screw 18 during insert molding.

  FIG. 3 schematically shows an insert mold 19 for integrating the lead screw 18 with the rotor 14. As illustrated, the mold 19 includes a pair of a fixed mold 191 and a movable mold 192, and the fixed mold 191 is provided with a sealing pin 193. The sealing pin 193 has a relatively small diameter portion 193a and a relatively large diameter portion 193b. The small diameter portion 193a is inserted into the through hole 18a of the lead screw 18 and the large diameter portion. 193b is brought into close contact with the peripheral portion of the through hole 18a in the bottom surface 18b of the lead screw 18 located inside the holder 143. Thereby, the molten resin injected from the gate 191a at the time of molding does not flow into the through hole 18a of the lead screw 18.

  However, in order to reliably prevent the molten resin from flowing into the through hole 18a, it is necessary to secure a sufficient size of the exposed portion that is in close contact with the sealing pin 193. Desirably, the length (L1) from the outer edge of the exposed portion to the outer edge of the through hole 18a may be ½ or more of the length (L2) from the outer edge of the support portion 181 to the outer edge of the through hole 18a. That is, it is sufficient that the relationship satisfies the relationship (L1) ≧ (L2) / 2.

  Thus, due to the presence of the sealing pin 193, the rotor 14 has a recess 143b (the bottom surface of the recess 143b is an exposed portion of the lead screw 18) that is a trace of the sealing pin 193 being pulled out on the bottom surface 144 side. Is formed. An annular sliding portion 15 is formed along the opening edge of the concave portion 143b, and the sliding area with the main body case 52 (thrust bearing 17) is minimized. Thereby, even when the rotor 14 and the lead screw 18 are integrated by insert molding, the energy loss by the said sliding resistance does not become large compared with the past. The shape of the sliding portion 15 is not particularly limited. For example, it may be configured such that it is scattered in the circumferential direction along the opening edge of the recess 143b.

  The carriage 20 is a resin member in which the main body portion 22 and the output shaft portion 24 are integrally formed. In the center of the columnar main body portion 22, a female screw portion 201 is formed so as to penetrate through a male screw formed on the screw portion 182. The output shaft portion 24 is a substantially semicircular shaft that protrudes from the output-side end surface of the main body portion 22 and is formed in two (in a forked shape) so that the semicircular straight portions (opposing surfaces 241a) face each other. Has been. Each of the two output shaft portions 24 is formed with a mounting hole 241b penetrating in a direction orthogonal to the axial direction. A connecting shaft (not shown) for connecting the carriage 20 and a valve body as a driven body is supported in the mounting hole 241b. The carriage 20 having such a configuration is attached to the lead screw 18 by screwing the female screw portion 201 into the screw portion 182.

  The first rotation prevention member 30 is a member integrally formed of a synthetic resin material, and has a cylindrical portion 32 and a flange portion 34. Two substantially semicircular guide holes 321 are formed in the top plate portion of the cylindrical portion 32 so that the semicircular straight portions face each other. The two output shaft portions 24 of the carriage 20 described above are inserted into the guide holes 321 respectively. The first rotation prevention member 30 is attached by fitting the flange portion 34 into the step portion of the main body case 52.

  The first rotation preventing member 30 attached in this manner is a member that prevents the carriage 20 from rotating with the lead screw 18. Therefore, the rotation of the first rotation prevention member 30 is restricted by the second rotation prevention member 40 so that the first rotation prevention member 30 itself does not rotate together with the carriage 20. The second rotation prevention member 40 is a plate-like member formed by pressing a metal plate or the like, and is attached so as to cover the opening of the main body case 52. As described above, the second rotation blocking member 40 is made of metal, as shown in FIG. 2, in which the sealed state of the sealed space 90 formed by a gas pipe or the like is maintained by the second rotation blocking member 40. Because you have to do it. That is, for example, in order to prevent the rotation prevention member 40 from being damaged by heat during a fire or the like, and causing the combustible gas in the sealed space 90 to leak and the damage to be expanded, the rotation prevention member 40 is made of a metal material. There is a need.

  A recess 42 having a predetermined size is formed at the center of the second rotation prevention member 40, and a substantially rectangular shape (four corners) through which the first rotation prevention member 30 is inserted at the center of the recess 42. (The corners of which are rounded) are formed. The cylindrical portion 32 of the first rotation prevention member 30 is inserted into the engagement hole 44, whereby the rotation of the first rotation prevention member 30 is restricted.

  This point will be specifically described with reference to FIG. 4 in addition to FIG. 1 and FIG. FIG. 4 is a plan view of the linear actuator 1 according to the present embodiment as viewed from above. As shown in these drawings, the first rotation preventing member 30 is formed so as to face a D-cut portion 322 in which the outer peripheral surface of the cylindrical portion 32 is cut out in a plane. Further, a protruding portion 321a protruding outward is formed at the center of the D-cut portion 322.

  On the other hand, as can be seen from FIG. 4, the engagement hole 44 of the second rotation prevention member 40 is formed with a straight line portion 441 whose shape seen from above is a straight line shape. An engagement recess 441a that is recessed outward is formed. The first rotation prevention member 30 is inserted into the engagement hole 44 of the rotation prevention member 40 in a state where the D-cut portion 322 is brought into contact with the linear portion 441 and the protrusion 321a is engaged with the engagement recess 441a. ing.

  As described above, the first rotation preventing member 30 is disposed in a state in which the D-cut portion 322 formed on the outer peripheral surface of the cylindrical portion 32 is in contact with the linear portion 441 of the engagement hole 44. In addition, a protruding portion 321 a provided to protrude from the D-cut portion 322 is engaged with an engaging recess 441 a that is recessed outward from the straight portion 441 of the engaging hole 44. The rotation of the first rotation preventing member 30 is restricted by the engagement between the D-cut portion 322 and the linear portion 441 and the engagement between the protruding portion 321a and the engagement recess 441a.

  Thus, the first rotation prevention member 30 whose rotation is restricted by the second rotation prevention member 40 functions as a rotation preventing member of the output shaft portion 24. As shown in FIG. 4, the two output shaft portions 24 are formed in a substantially semicircular cross section, and their rotation is restricted by being inserted into guide holes 321 that are also formed in a substantially semicircular shape. ing. Specifically, the rotation of the output shaft portion 24 is restricted by bringing the opposing surfaces 241 a of the two output shaft portions 24 into contact with the inner surface of the guide hole 321.

  The linear actuator 1 configured as described above operates as follows. When the motor 10 that is a drive source is driven, the rotor 14 rotates. When the rotor 14 rotates, the lead screw 18 integrated with the rotor 14 also rotates. When the lead screw 18 rotates, the carriage 20 in which the main body portion 22 is screwed with the screw portion 182 of the lead screw 18 also tries to rotate together with the lead screw 18. However, since the output shaft portion 24 of the carriage 20 is inserted into the guide hole 321 of the first rotation prevention member 30 whose rotation is restricted by the second rotation prevention member 40, the carriage 20 does not rotate. . Therefore, the carriage 20 moves forward in the axial direction of the fixed shaft 16 as the lead screw 18 rotates. When the carriage 20 moves forward, the valve body that is a driven body connected to the carriage 20 moves forward using the mounting hole 241b of the output shaft portion 24, and the gas flow path is blocked.

  When the carriage 20 is moved backward, the lead screw 18 is rotated in the opposite direction to the case where the carriage 20 is moved forward. As a result, the carriage 20 whose rotation is restricted by the first rotation preventing member 30 moves backward in the axial direction of the fixed shaft 16, and the gas flow path is opened.

  Hereinafter, the present invention will be described using examples. In addition, this invention is not limited to a following example.

(Example)
The linear actuator which has the structure similar to the linear actuator 1 concerning the said embodiment was created as an Example. This embodiment is characterized in that the rotor 14 and the lead screw 18 are integrally formed. The lead screw 18 is integrated with the rotor 14 (holder 143) by insert molding. Further, a resin washer is used for the thrust bearing 17 interposed between the rotor 14 and the main body case 52.

1) Preliminary Study First, the study that led to obtaining the linear actuator according to this example will be described. In the linear actuator according to the embodiment of the present invention, the rotor 14 (holder 143) and the lead screw 18 are separately configured (not integrated), and each is rotatably supported on the fixed shaft 16 (the rotor 14 and the lead). It is obtained on the basis of the configuration (Examination Example 1) described in FIG. 5A that can be separated from the screw 18. In such a configuration, the lead screw 18 has a D-cut engagement portion 181 a formed by cutting a part of the disk straightly below the screw portion 182. The rotor 14 (holder 143) has a D-cut recess 143b engaged therewith. That is, the rotation of the rotor 14 is transmitted to the lead screw 18 by the engagement between the D-cut engagement portion 181a and the D-cut recess 143b. The other configuration is the same as that of the linear actuator 1 according to the above embodiment.

  The linear actuator according to Study Example 1 has a problem that noise is high when the actuator is driven. Therefore, the linear actuator concerning the following study examples 2-5 which deform | transformed the said study example 1 was created, and the cause of the noise was identified by evaluating the quiet characteristic of these actuators.

  In Examination Example 2, instead of a thrust bearing (washer) 17 for reducing sliding resistance interposed between the rotor 14 and the body case 52, a plate-like elastic member 171 having elasticity (cushioning property) is disposed. (See FIG. 5B). The elastic member 171 includes a disc portion 171a having a through-hole through which the fixed shaft 16 is inserted in the center, and a tongue-like elastic piece 171b extending from the outer periphery of the disc portion 171a every 120 degrees in the circumferential direction. It is configured.

  In Examination Example 3, an elastic member 171 having a larger elastic force than that of Comparative Example 2 is disposed between the rotor 14 and the main body case 52.

  In Study Example 4, an O-ring 172 formed of an elastic body as a buffer member is disposed on the upper surface (between the lead screw 18 and the carriage 20) of the D-cut engagement portion 181a of the lead screw 18 (see FIG. 5 (c)).

  In Examination Example 5, an O-ring 172 formed of an elastic body as a buffer member is disposed between the rotor 14 and the lead screw 18. Note that the O-ring 172 is the same as that in the fourth study example (see FIG. 5D).

  Note that the other configurations of the study examples 2 to 5 are the same as those of the linear actuator according to the study example 1 described above.

  The quiet characteristics (presence / absence of noise) of the linear actuator according to the above examination examples 1 to 5 were examined. In each study example, the motor 10 was driven at a power supply voltage of 2 V and a rotational speed of 333 pps, and the sound pressure (dBA) during the operation of the actuator was measured. The distance between the actuator and the sound collecting microphone is 30 cm. In each of the examination examples 1 to 5, 1) the motor 10 is rotated in the direction in which the carriage 20 is lowered, and the carriage 20 is lowered to the lower limit (a state where the carriage 20 cannot be lowered any more). 2) The sound pressure at the time when the carriage 20 is pulled up (hereinafter referred to as the pull-out step-out state), and 2) The motor 10 is rotated in the direction in which the carriage 20 is raised, and the carriage 20 is moved to the upper limit (the carriage 20 cannot be raised any more). The sound pressure was measured when the ascending motor 10 was in a step-out state (hereinafter referred to as an extrusion step-out state). Table 1 shows the measurement results.

  First, when the result about the examination example 1 is seen, it turns out that a sound pressure is large when it is in a drawing out-of-step state compared with the case where it is in an out-of-step state. In consideration of the quiet characteristics required for the product, the sound pressure level in the push-out step-out state is not felt as noise, but the sound pressure level in the pull-out step-out state may be felt as noise.

  In the study examples 2 and 3, in addition to the configuration of the study example 1, an elastic member 171 is disposed between the rotor 14 and the bottom surface of the main body case 52 instead of the thrust bearing (washer) 17. From comparison with Example 1, it can be seen that there is no noise reduction effect due to the presence of the elastic member 171. That is, it can be seen that there is a low possibility that large noise is generated on the bottom surface side of the rotor 14 (the thrust bearing (washer) 17 or the like is not the main cause of noise).

  Further, Study Example 4 differs from the study example 1 only in that an O-ring 172 is disposed between the lead screw 18 and the carriage 20, and the other construction is the same. There is no noise reduction effect. That is, it can be seen that the collision between the lead screw 18 (D-cut engagement portion 181a) and the carriage 20 is not the main cause of noise.

  Compared to the study example 1, the study example 5 in which the O-ring 172 that is a buffer material is disposed between the rotor 14 and the lead screw 18 is compared with the study examples 2 to 4 in the pull-out step-out state. Sound pressure was greatly reduced. Specifically, it was reduced to the same level as the sound pressure in the extruded step-out state, and a product sufficiently satisfying the quiet characteristics required for the product was obtained.

  Considering these measurement results, it is estimated that the noise generated by the linear actuator according to Study Example 1 is generated by the collision between the rotor 14 and the lead screw 18. Specifically, it is considered that the problem is caused by the following mechanism. As shown in FIG. 6A, when the lead screw 18 is rotating in the direction in which the carriage 20 is pushed out (when it is about to rotate), the reaction of the carriage 20 that moves upward (is about to move). As a result, a downward force is applied to the lead screw 18. Then, since the rotor 14 is sandwiched between the lead screw 18 that has received a downward force and the bottom surface of the main body case 52, the rotor 14 does not rattle even in a step-out state. On the other hand, as shown in FIG. 6B, when the lead screw 18 is rotating in the direction in which the carriage 20 is retracted (when it is about to rotate), the carriage 20 moves downward (is about to move). Due to this reaction, an upward force is applied to the lead screw 18. As a result, a clearance is generated between the lead screw 18 and the rotor 14, and the out-of-step rotor 14 is thought to vibrate in the vertical direction to generate noise.

  After identifying the cause of the noise, the above-described embodiment (the present invention) in which the rotor 14 and the lead screw 18 are integrated has been obtained.

2) Evaluation of Quiet Characteristics of Examples The quiet characteristics (presence / absence of noise) of the linear actuator according to the above examples were evaluated. Two samples of Examples having exactly the same configuration were prepared (Example A and Example B), and the quiet characteristics were evaluated for each sample. In addition, as shown below, two types of comparative examples were created. In this comparative example, whether or not the quiet characteristics are changed by changing the thrust bearing 17 that supports the bottom surface of the rotor 14 is examined. For reference, both types are listed as Comparative Example 1 and Comparative Example 2.

  Comparative Example 1 is a linear actuator having a structure similar to that of the above-described Study Example 1, that is, a linear actuator in which the rotor 14 and the lead screw 18 are separately supported on the fixed shaft 16. The linear actuator of Comparative Example 1 differs from the example in that the thrust bearing 17 that supports the bottom surface of the rotor 14 is made of metal (phosphor bronze).

  Comparative Example 2 is a linear actuator in which the rotor 14 and the lead screw 18 are separately supported on the fixed shaft 16 as in Comparative Example 1. The difference from Comparative Example 1 is that the thrust bearing 17 is made of resin (polyethylene terephthalate) as in the example. Two samples of Comparative Example 2 having exactly the same configuration were prepared (Comparative Example 2A and Comparative Example 2B), and the quiet characteristics were evaluated for each sample.

  The quiet characteristic evaluation was performed by measuring the sound pressure when the motor 10 was driven at a power supply voltage of 2 V and a rotation speed of 333 pps, similarly to the evaluation performed for the above examination example. It should be noted that the point that the distance between the actuator and the sound collecting microphone is 10 cm is different from the measurement performed for the study example. Under such conditions, for each of the examples and the comparative examples, 1) a pull-out step-out state, 2) a push-out step-out state, and 3) a normal state (the motor 10 is not in a step-out state, and the carriage 20 moves forward and backward). Sound pressure (dBA) was measured. The results are shown in Table 2. Moreover, the frequency characteristic in the audible range of the generated sound was measured. The results are shown in FIGS. The results of Example are shown in FIG. 7, the results of Comparative Example 1 are shown in FIG. 8, and the results of Comparative Example 2 are shown in FIG.

  From Table 2 and FIGS. 7 to 9, the linear actuator according to Comparative Example 1 and Comparative Example 2 has no problem in the push-out step-out state and the normal state, but in the pull-out step-out state, a loud sound (noise) is generated in the audible range. appear. From the above examination results, it is considered that noise is generated by the collision between the rotor 14 and the lead screw 18. On the other hand, in the linear actuator according to the example, even in the pull-out step-out state, the sound pressure level is almost the same as in the push-out step-out state and the normal state, and it can be seen that no loud sound (noise) is generated.

  As can be seen from the results of Comparative Example 1 and Comparative Example 2, there is no improvement in the quiet characteristics by changing the material of the thrust bearing 17.

  As described above, according to the present invention, since the rotor 14 and the lead screw 18 are integrated, the generation of noise due to the collision between the rotor 14 and the lead screw 18 is prevented. In some cases, the linear actuator 1 with low noise and excellent quietness can be obtained.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

  For example, in the above embodiment, it has been described that the rotor 14 (holder 143) is made of a resin material and the lead screw 18 is made of a metal material. However, if the mechanical strength of the lead screw portion can be ensured, both Can be integrally formed of the same resin material.

DESCRIPTION OF SYMBOLS 1 Linear actuator 10 Motor 14 Rotor 15 Sliding part 16 Fixed shaft 18 Lead screw 18a Through-hole 20 Carriage 30 1st rotation prevention member 40 2nd rotation prevention member

Claims (6)

In a linear actuator provided with a motor as a drive source in a case and a linear motion conversion mechanism that converts rotational power of the motor into linear power and transmits it to a driven body.
The linear motion conversion mechanism includes a lead screw that is rotated by a rotor of the motor, a carriage that is screwed into the lead screw and connected to the driven body, and a rotation blocking member that blocks rotation of the carriage. The rotor and the lead screw are integrally formed and are rotatably supported by a fixed shaft fixed to the case.   The linear actuator according to claim 1, wherein the rotor and the lead screw are formed of different materials.   The linear actuator according to claim 2, wherein the rotor is made of a resin and the lead screw is made of a metal material.   In the case where the lead screw is integrally formed with the rotor by insert molding, the lead screw protrudes from a support portion at least partially embedded in the rotor and an end surface on one side of the support portion. A through hole through which the fixed shaft is inserted, and at least a peripheral portion of the through hole on the other end face of the support portion is exposed to the outside. The linear actuator according to claim 3.   When the support portion is formed in a cylindrical shape and the exposed portion on the other end face of the support portion is formed in a circular shape, the length from the outer edge of the exposed portion to the outer edge of the through hole is: 5. The linear actuator according to claim 4, wherein the linear actuator is at least ½ of a length from an outer edge of the support portion to an outer edge of the through hole. On the bottom surface of the rotor, a concave portion is formed with the exposed portion on the other end face of the support portion serving as a bottom surface, and a sliding portion protruding in the axial direction of the fixed shaft is formed on the opening periphery of the concave portion. The linear actuator according to claim 4 or 5, wherein

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