JP2007118228A - Manufacturing method of molded plastic gear - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a molded plastic gear capable of effectively suppressing the occurrence of noise while ensuring high dimensional precision. <P>SOLUTION: The molded plastic gear 30 is manufactured by providing resonance preventing holes 70 to a fundamental gear, which is used for transmitting the drive force from the drive motor 21 of various devices mounted in a printer 10 in order to prevent the resonance with the vibration caused by the driving of the drive motor 21. This manufacturing method of the molded plastic gear 30 is composed of a fundamental gear forming process for injecting a heated molten synthetic resin raw material in a mold having a cavity corresponding to the appearance shape of a web part 60 in a state that the resonance preventing holes 70 are not provided to mold the fundamental gear and a resonance preventing hole drilling process for drilling the resonance preventing holes 70 in the web part 60 of the fundamental gear. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a molded plastic gear made of a synthetic resin material as a raw material and mainly manufactured by an injection molding method, and in particular, a copying machine, a facsimile machine, which is a precision instrument, and an image forming apparatus such as a printer. The present invention relates to a method of manufacturing a molded plastic gear suitable for application to a vehicle.

  Conventionally, a molded plastic gear as described in Patent Document 1 is known. This molded plastic gear is improved so that it can be suitably applied to a precision drive system of an image forming apparatus such as a copying machine or a printer by increasing accuracy and rigidity, and is concentric from the root position toward the center. A part corresponding to the mold gate (injection hole) for injecting resin into the web part (circular part formed thinner than the rim) inside the rim The thickness of the web portion outside the rim is set to be thicker than the thickness inside the rim.

In such a molded plastic gear, when the gear is manufactured by injection molding, the molten resin raw material injected from the mold through the gate into the web portion inside the rim is moved outward in the radial direction. The gap dimension in the mold cavity increases from a thin part toward a thick part on the outer side of the rim. Therefore, since the molten resin injected into the cavity of the mold flows smoothly and uniformly in the cavity (paragraph [0019] of Patent Document 1), the resulting molded plastic gear has high accuracy. Further, it is described that it has high rigidity and can be suitably applied to a precision drive system of OA equipment such as a printer and a copying machine (paragraph [0037] of Patent Document 1).
Japanese Patent Laid-Open No. 10-278124

  By the way, of course, high precision is required for molded plastic gears that are applied to the drive systems of precision equipment such as image forming devices. In addition, image forming devices are quieter working environments. Therefore, it is required that noise is not generated. In particular, in the case of a tandem type color copying machine in which a plurality of photosensitive drums different for each color are arranged in parallel so as to rotate precisely and synchronously, the respective gears coaxial with the respective photosensitive drums meshed with each other, The diameter of the gear is increased in order to reduce the rotation transmission error. However, when the gear is increased in diameter, the area of the web portion increases accordingly, and vibration caused by the drive motor resonates in the web portion, resulting in large noise. Is likely to occur.

  Therefore, when the molded plastic gear described in Patent Document 1 is evaluated for an image forming apparatus, there is no problem with respect to high accuracy, but noise generation is not taken into consideration, and quietness is achieved. Therefore, there is a problem that it is difficult to use as a gear for an image forming apparatus installed in a different environment.

  Incidentally, as a soundproofing measure for the gear provided with the web portion, it is conceivable to make the natural frequency of the web portion different from the frequency by the drive of the drive motor. By doing so, the web portion does not resonate with the vibration caused by the driving of the drive motor, so that the generation of noise from the web portion can be reliably suppressed. As a simple measure for making the natural frequency of the web portion different from the frequency generated by driving the drive motor, it is possible to open a plurality of resonance prevention holes at equal pitches in the circumferential direction in the web portion. By providing the anti-resonance hole in the web portion, the area of the web portion is reduced, and accordingly, the natural frequency becomes higher than the vibration frequency due to driving of the drive motor, and resonance of the web portion is avoided.

  However, there is no problem with the uniformity of quality even if the anti-resonance hole is formed by cutting the gear manufactured by using only a solid material of uniform quality as a raw material, but it is manufactured by an injection molding method. In the case of molded plastic gears, a core corresponding to the resonance prevention hole is provided in the cavity of the mold, so that the synthetic resin material melted in the mold is spread with equal pressure by the core being in the way. The resulting molded plastic gear has a problem that it can prevent resonance with the drive motor but lacks precision.

  The present invention has been made to solve such problems, and a method for producing a molded plastic gear for an image forming apparatus capable of effectively suppressing noise generation while ensuring high dimensional accuracy. The purpose is to provide.

  According to a first aspect of the present invention, there is provided the web portion of the basic gear having an annular web portion used for transmitting the driving force from the drive source in various devices incorporated in the image forming apparatus. A method of manufacturing a molded plastic gear provided with a resonance prevention hole to prevent resonance with vibration caused by driving, having a cavity corresponding to the external shape of the web portion without the resonance prevention hole. Through a basic gear forming step of forming a basic gear by injecting and injecting a synthetic resin raw material heated and melted into a mold, and a resonance preventing hole forming step of forming a resonance preventing hole in the web portion of the basic gear It is characterized by manufacturing a molded plastic gear.

  According to such a configuration, the resonance prevention hole provided in the web portion is formed by performing the punching process on the web portion after the molding process, and thus obtained as a result of the punching process. Molded plastic gears are compared to machined products in terms of dimensional accuracy and material uniformity, as in the case of manufacturing gears by injection molding by forming a core for holes in the mold cavity during the molding process. The product is not inferior, and the generation of noise is suppressed by the presence of the anti-resonance hole while ensuring high precision quality.

  According to a second aspect of the present invention, in the first aspect of the invention, the resonance prevention hole is shaped so that the center of gravity of the molded plastic gear does not shift from the center of gravity of the basic gear. It is characterized by.

  According to such a configuration, the molded plastic gear has the resonance prevention hole set so that the position of the center of gravity is not decentered, so that it is possible to avoid the inconvenience that the power cannot be transmitted with high accuracy.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, three or more resonance prevention holes are formed.

  According to this configuration, when three or more resonance prevention holes are formed, the resonance prevention holes are evenly distributed in the circumferential direction, and eccentricity is easily prevented.

  According to the first aspect of the present invention, the resonance preventing hole provided in the web portion is formed by performing the punching process on the web portion after the molding process. The resulting molded plastic gear is inferior in terms of dimensional accuracy and material uniformity, such as when a gear core is manufactured by injection molding by forming a hole core in the mold cavity during the molding process. The generation of noise can be suppressed by the presence of the anti-resonance hole while ensuring high precision quality.

  According to the invention described in claim 2, since the resonance preventing hole is shaped so that the center of gravity position of the web portion does not shift, the molded plastic gear rotates eccentrically due to the eccentricity of the center of gravity position. The occurrence of inconvenience that the molded plastic gear cannot transmit power with high accuracy can be avoided.

  According to the invention described in claim 3, when three or more resonance preventing holes are provided, it is possible to uniformly and efficiently disperse in the circumferential direction, and it is possible to easily prevent the eccentricity of the gear. it can.

  First, a printer 10 to which a molded plastic gear manufactured by the method of the present invention is applied will be described with reference to FIGS. 1 and 2. FIG. 1 is a front sectional view for explaining an outline of a printer to which a molded plastic gear according to the present invention is applied, and FIG. 2 is a drive unit 20 for transmitting power to various devices in the printer 10. It is a perspective view which shows one Embodiment.

  First, as shown in FIG. 1, the printer 10 is formed by an image forming unit 12 that forms an image based on image information transmitted from a computer or the like in a box-shaped casing 11, and the image forming unit 12 forms the image. The fixing unit 13 for fixing the image transferred to the paper and the paper storage unit 14 for storing the transfer paper are internally provided.

  The image forming unit 12 forms a toner image on a sheet fed from the sheet storage unit 14, and in the present embodiment, the image forming unit 12 sequentially arranges from the upstream side (the left side of the sheet of FIG. 1) to the downstream side. A magenta unit 12M, a cyan unit 12C, a yellow unit 12Y, and a black unit 12K are provided.

  Each unit 12M, 12C, 12Y, and 12K includes a photosensitive drum 121 and a developing device 122, respectively. Each photosensitive drum 121 is supplied with toner from a corresponding developing device 122 while rotating counterclockwise in FIG. Each developing device 122 is replenished with toner from a toner cartridge 122a disposed at the top thereof.

  A charger 123 is provided immediately above each photoconductor drum 121, and an exposure device 124 is provided between the charger 123 and the developing device 122. Each photosensitive drum 121 is charged uniformly by the charger 123, and laser light corresponding to each color based on image data transmitted from a computer (not shown) is charged from each exposure device 124. By irradiating the peripheral surface of each photoconductive drum 121, an electrostatic latent image is formed on the peripheral surface of each photoconductive drum 121. By supplying toner from the developing device 122 to the electrostatic latent image, a toner image is formed on the peripheral surface of the photosensitive drum 121.

  A transfer belt 125 stretched between the driving roller 125 a and the pair of driven rollers 125 b is provided below the respective photosensitive drums 121 so as to be in contact with the respective photosensitive drums 121. The transfer belt 125 is paired with a driving roller 125 a and a pair of rollers while being synchronized with each photoconductive drum 121 while being pressed against the peripheral surface of the photoconductive drum 121 by a transfer roller 126 provided corresponding to each photoconductive drum 121. It rotates around the driven roller 125b.

  Accordingly, when the transfer belt 125 circulates, the magenta toner image is transferred onto the surface of the transfer belt 125 by the photosensitive drum 121 of the magenta unit 12M, and then the photosensitive drum of the cyan unit 12C is placed at the same position on the transfer belt 125. The transfer of the cyan toner image by 121 is performed in the overcoating state, and then the transfer of the yellow toner image by the photosensitive drum 121 of the yellow unit 12Y to the same position of the transfer belt 125 is performed in the overcoating state. The transfer of the black toner image by the photosensitive drum 121 of the black unit 12K is performed in an overcoated state, whereby a color toner image is formed on the surface of the transfer belt 125. The color toner image formed on the surface of the transfer belt 125 is transferred to the paper P conveyed from the paper storage unit 14.

  A cleaning device 127 that removes and cleans residual toner on the peripheral surface of the photosensitive drum 121 is provided at the right side of each photosensitive drum 121 in FIG. The peripheral surface of the photosensitive drum 121 cleaned by the cleaning device 127 is directed to the charger 123 for a new charging process.

  The waste toner removed from the peripheral surface of the photosensitive drum 121 by the cleaning device 127 is collected in a toner collection bottle (not shown) through a predetermined path and stored.

  A sheet conveyance path 111 extending from the right side to the left side in FIG. 1 is provided at a position below the image forming unit 12. A registration roller pair 112 is provided at a substantially central position in the left-right direction of the sheet conveyance path 111, and a transfer belt 125 on which a sheet from the sheet storage unit 14 is wound around a driving roller 125 a by driving the registration roller pair 112. It is to be transported towards In the sheet conveyance path 111, a second transfer roller 113 that is in contact with the surface of the transfer belt 125 is provided at a position facing the driving roller 125 a, and the sheet P being conveyed along the sheet conveyance path 111 is separated from the transfer belt 125. The toner image on the transfer belt 125 is transferred to the paper P by being pressed and held between the second transfer roller 113 and the second transfer roller 113.

  The fixing unit 13 performs a fixing process on the toner image on the paper transferred by the image forming unit 12, and includes a heating roller 131 including an energizing heating element serving as a heating source, and the heating roller 131. And a pressurizing member 132 arranged opposite to each other. The heating roller 131 includes a halogen lamp as a heating element.

  The pressure member 132 includes a pair of pressure rollers 133 and a pressure belt 134 adjusted to the pair of pressure rollers 133 in a state where the surface is in pressure contact with the peripheral surface of the heat roller 131. The sheet P after the transfer process that has passed between the second transfer roller 113 and the transfer belt 125 passes between the rotating heating roller 131 and the rotating pressure belt 134. Fixing processing is performed by obtaining heat from the heating roller 131.

  The paper P with the color image for which the fixing process has been completed is discharged toward a paper discharge tray 115 provided at the top of the housing 11 through a paper discharge conveyance path 114 extending from the left side of the fixing unit 13. Will be.

  The paper storage unit 14 has a paper tray 141 that is detachably mounted at a position below the paper transport path 111 in the housing 11. A sheet bundle is stored in the sheet tray 141. The sheet P is fed out from the sheet bundle stored in the sheet tray 141 one by one by driving the pickup roller 142, and sent to the image forming unit 12 through the sheet conveyance path 111.

  FIG. 2 is a perspective view showing an embodiment of the drive unit 20 intended for the image forming unit 12. Incidentally, the drive unit 20 shown in FIG. 2 is provided with four large-diameter gears 33 in the drive unit 20, and the photosensitive drums 121 are precisely and synchronously rotated by the four large-diameter gears 33. It is made to be done. This is because the printer 10 is in a situation where noise is easily generated by the large-diameter gear 33. If the molded plastic gear 30 according to the present invention is employed in the four large-diameter gears 33, the noise is reduced. Thus, the molded plastic gear 30 according to the present invention is applied to the printer 10 with special significance. Can understand that there is.

  The drive unit 20 is configured by mounting a large number of molded plastic gears 30 and a drive motor 21 on a drive unit frame 15 that has a long plate shape in the lateral direction. The drive motor 21 is fixed horizontally at one end of the drive unit frame 15 (the back side of the right end in the example shown in FIG. 2), and the drive shaft 211 is passed through the drive unit frame 15. .

  The molded plastic gear 30 includes a drive gear 31 that is concentrically fitted to the drive shaft 211 so as to rotate integrally therewith, and a drive gear 31 that is rotatably supported around the idle shaft 22 below the drive gear 31. The idle gear 32 that meshes, the large-diameter gear 33 that meshes with the idle gear 32 and rotates integrally with the drum shaft 121a supported by the drive unit 20, and the large-diameter gear 33 protrudes to the left position in FIG. A small-diameter gear 34 that rotates about the provided first shaft 23, a first medium-diameter gear 35 that meshes with the small-diameter gear 34 and rotates about the second shaft 24, and meshes with the first medium-diameter gear 35. The second medium-diameter gear 36 rotating around the third shaft 25 is employed.

  Four large-diameter gears 33 are arranged side by side on the drive unit frame 15 in the lateral direction, and are each supported so as to be integrally rotatable about the drum shaft 121a. Then, the same small diameter gear 34 is sequentially meshed with the second and subsequent large diameter gears 33 from the right in FIG. 2, and the same first medium diameter gear 35 is meshed with the small diameter gear 34. A second medium diameter gear 36 meshes with the first medium diameter gear 35. That is, four groups of gear groups are formed by combining gears including the large-diameter gear 33, the small-diameter gear 34, the first medium-diameter gear 35, and the second medium-diameter gear 36. A photosensitive drum 121 is concentrically coupled to each drum shaft 121a that integrally supports each large-diameter gear 33 so as to be integrally rotatable.

  According to the drive unit 20, the drive rotation of the drive motor 21 is transmitted to the right-end large-diameter gear 33 in FIG. 2 via the drive shaft 211, the drive gear 31, and the idle gear 32. The rotation of the gear 33 is transmitted to the second large-diameter gear 33 from the right through the small-diameter gear 34, the first medium-diameter gear 35, and the second medium-diameter gear 36. Thus, the four photosensitive drums 121 rotate synchronously at the same rotational speed in the same direction.

  Accordingly, the vibration of the drive motor 21 is transmitted to the four large-diameter gears 33 through the respective gears. In particular, the four large-diameter gears 33 serve as speakers, and the drive motor 21 A large noise is generated in resonance with the vibration. An object of the present invention is to prevent the generation of such noise.

  FIG. 3 is a view showing an embodiment of a molded plastic gear 30 according to the present invention, in which (A) is a perspective view and (B) is a cross-sectional view taken along line AA of (A). The molded plastic gear 30 according to the present invention is a so-called injection in which a predetermined hard thermoplastic synthetic resin material (for example, POM (polyacetal)) heated to a softening temperature is injected into a cavity of a predetermined mold. A raw material gear is once manufactured by a molding method, and is manufactured by subjecting the web portion 60 of the raw material gear to a perforation process.

  In the present embodiment, POM (polyoxymethylene, also known as polyacetal) is adopted as a raw material for the molded plastic gear 30. The reason for this is that POM has very good mechanical properties at both high and low temperatures and is stable, and the relationship between stress and strain is close to that of metal, and has good elastic recovery, similar to that of metal. In addition to being superior to other synthetic resins in terms of creep resistance and fatigue resistance, it also has excellent self-lubricating properties and can be used in a non-lubricated state. It is because it has the nature.

  Incidentally, POM has a shrinkage ratio of 1.8% to 2.5% at the time of injection molding, which is lower than that of a general synthetic resin material such as PE (polyethylene). (Acrylonitrile butadiene styrene copolymer: shrinkage 0.2% to 0.9%), PC (polycarbonate: shrinkage 0.5% to 0.7%), PS (polystyrene: shrinkage 0.2% to 0.2%) 0.7%) and the like, and by using these materials, the molded plastic gear 30 becomes more accurate.

  As shown in FIG. 3, the molded plastic gear 30 is concentric with an annular tooth portion 40 in which a plurality of teeth 41 are formed on the outer peripheral surface at an equal pitch in the circumferential direction, and a central position of the tooth portion 40. A basic portion provided with a shaft portion 50 formed by the web portion 60, a web portion 60 installed between the shaft portion 50 and the tooth portion 40, and a plurality of resonance prevention holes 70 formed in the web portion 60. It has a configuration. A shaft hole 51, which is a through hole extending in the axial direction, is formed at the center position of the shaft portion 50, and a drive shaft of a predetermined drive motor is inserted into the shaft hole 51 in a non-rotating state, It is supported so that it can rotate relative to the support shaft.

  Incidentally, when the molded plastic gear 30 is used in such a manner that it is fitted on the drive shaft or the like in a non-rotating state, for example, a flat key portion is formed on the inner peripheral surface of the shaft hole 51, while the drive shaft or the like is formed. A D-cut surface or the like corresponding to the key portion is formed on the outer peripheral surface, and the drive shaft or the like and the molded plastic gear 30 can be integrally rotated by the mutual contact between the D-cut surface and the key portion. However, the present invention is not limited to this, and both of them may be screwed or a key may be inserted into a key groove recessed in both of them.

  Further, the width dimension W1 of the tooth portion 40 is set to be the same as the width dimension W2 of the shaft portion 50 in the present embodiment.

  As shown in FIG. 3B, the web portion 60 is formed between the tooth portion 40 and the shaft portion 50 at the central portion in the axial center direction of the molded plastic gear 30 and has a thickness dimension d1 of the tooth portion 40. Is set to approximately one third of the width dimension W1. However, the thickness dimension d1 of the web part 60 is not limited to approximately 1/3 of the width dimension W1 of the tooth part 40, and is 1/3 of the width dimension W1 of the tooth part 40 depending on the application and situation. It may be thinner or vice versa. This is because the web portion 60 is thinner than the tooth portion 40 so as to save the amount of synthetic resin raw material used, so-called meat stealing, and to improve the molding accuracy.

  The anti-resonance hole 70 increases the natural frequency of the web portion 60 by reducing the area of the web portion 60 so that the web portion 60 does not resonate with the vibration caused by the drive rotation of the drive motor 21. belongs to. Incidentally, in this embodiment, the rotation speed of the drive motor 21 is 699 rpm, and the number of teeth of the drive gear 31 provided concentrically on the drive shaft 211 is 12. As a result, the frequency of vibration generated by driving the drive motor 21 is 138.9 Hz (699 revolutions / min × 12 sheets ÷ 60 sec / min). Accordingly, the resonance preventing hole 70 is formed in the web portion 60 so that the natural frequency thereof is higher than 138.9 Hz.

  In the present embodiment, six such anti-resonance holes 70 having the same plane size with the center of curvature at the axial center position (center of gravity position) of the molded plastic gear 30 are provided at equal pitches in the circumferential direction. As a result, no displacement occurs with respect to the position of the center of gravity when the resonance preventing hole 70 is not provided.

  In the present invention, the molded plastic gear 30 is injected with a synthetic resin material heated and melted in a mold having a cavity corresponding to the external shape of the molded plastic gear 30 in a state where the resonance prevention hole 70 is not provided. It is manufactured by a manufacturing method in which a basic gear forming step of forming a basic gear by injection and a resonance prevention hole drilling step of drilling a resonance prevention hole 70 in the web portion 60 of the basic gear are performed. Yes.

  Such a manufacturing method is adopted for the following reason. That is, when a molded plastic gear having the resonance prevention hole 70 is manufactured from the beginning by performing an injection molding process using a mold having a core corresponding to the resonance prevention hole 70 in the cavity, the cavity exists in the presence of the core. Since the distribution of the raw material molten resin is hindered, and even if the raw material molten resin is spread all over the cavity, the distribution of density and tension in each part is uneven, Molded plastic gears taken out from the cavity after cooling have different shrinkage during cooling, resulting in deterioration of dimensional accuracy.

  On the other hand, in the manufacturing method of the present invention, the synthetic resin raw material heated and melted in a mold having a cavity corresponding to the external shape of the molded plastic gear 30 in which the resonance prevention hole 70 is not provided in the basic gear molding step. A basic gear is formed by injecting and injecting. Therefore, there is no local variation in internal stress in the web portion 60 in the basic gear forming process, and therefore the basic gear taken out of the mold is surely free from inconveniences such as being deformed when cooled. Therefore, the dimensional accuracy is high.

  Then, a two-stage manufacturing method of continuously forming the resonance prevention hole 70 in the web portion 60 of the basic gear in the resonance prevention hole drilling process is adopted, and the resonance prevention hole is formed by a predetermined method on the basic gear with high dimensional accuracy. 70 is drilled, the resulting molded plastic gear 30 has extremely good dimensional accuracy, and the natural frequency is caused by the drive motor 21 driven by the drilled resonance prevention hole 70. Therefore, resonance by the drive motor 21 of the resonance prevention hole 70 can be reliably prevented.

  FIG. 4 is a circular graph showing an example of the dimensional accuracy of a molded plastic gear having a resonance prevention hole. FIG. 4A shows a method for manufacturing a molded plastic gear according to the present invention (resonance after a basic gear is manufactured by a molding process). The measurement result of the diameter dimension of the molded plastic gear 30 manufactured by the two-stage method in which the prevention hole 70 is drilled) (Example), (B) is a mold having a core for the resonance prevention hole. The measurement results (comparative examples) of the diameter dimensions of the molded plastic gears manufactured in one stage using the same are shown.

  In the circular graph of FIG. 4, eight concentric circles that are spaced from the center in the radial direction by the same dimension are graduated, and the fourth circle from the center is defined as a dimensional error of “0”. Set the scales of “0.0500%”, “0.1000%”, “0.1500%” and “0.2000%” to each concentric circle one by one and inward from the fourth circle On the other hand, the scales of “−0.0500%”, “−0.1000%”, “−0.1500%”, and “−0.2000% (center position)” are sequentially set in each concentric circle.

  First, in the example in which the anti-resonance hole 70 is formed after the molding process is completed, as shown in FIG. 4A, the error in the diameter of the molded plastic gear 30 is “0.0000%”. It is confirmed that the molded plastic gear 30 manufactured by the method of the present invention has extremely good dimensional accuracy. did it.

  On the other hand, in a comparative example in which a molded plastic gear is manufactured in one stage using a mold having a core, the error in the diameter of the molded plastic gear is positive or negative with respect to a concentric circle of “0.0000%”. It was in a state of large variation, and it was confirmed that the dimensional accuracy was not necessarily good. Moreover, in the molded plastic gear, the portion where the anti-resonance hole is provided shrinks greatly toward the center in the radial direction during cooling, so that the error in the radial dimension is greatly shifted to the negative side, but the reaction causes the anti-resonance hole. It can be seen that the error in the part where no is provided is greatly shifted to the plus side.

  As described above in detail, the method of manufacturing the molded plastic gear 30 according to the present invention is heated and melted in a mold having a cavity corresponding to the external shape of the web portion 60 in a state where the resonance prevention hole 70 is not provided. A molded plastic gear is manufactured through a basic gear forming step of forming a basic gear by injection-injecting a synthetic resin material and a resonance prevention hole drilling step of drilling a resonance prevention hole 70 in the web portion 60 of the basic gear. Is.

  According to the method of manufacturing the molded plastic gear 30, the resonance prevention hole 70 provided in the web portion 60 is formed by performing a drilling process on the web portion 60 after the molding process. The molded plastic gear 30 obtained as a result of the drilling process has the same dimensional accuracy and uniform material as in the case where a hole core is formed in the cavity of the mold during the molding process and the gear is manufactured by injection molding. The product is not inferior in terms of performance, and the occurrence of noise can be suppressed by the presence of the resonance prevention hole 70 while ensuring high-precision quality.

  The resonance preventing hole 70 is shaped so that the center of gravity of the molded plastic gear 30 is not displaced from the position of the center of gravity of the basic gear. Occurrence of inconvenience that the molded plastic gear 30 cannot transmit power with high accuracy can be avoided.

  Further, since three or more resonance prevention holes 70 are formed, each resonance prevention hole 70 can be uniformly and efficiently dispersed in the circumferential direction. Can be easily and reliably prevented.

  The present invention is not limited to the above embodiment, and includes the following contents.

  (1) In the above embodiment, the printer 10 has been described as an example of the image forming apparatus to which the molded plastic gear 30 manufactured by the manufacturing method according to the present invention is applied. 30 is not limited to being applied to the printer 10, but may be applied to other image forming apparatuses such as a copying machine and a facsimile machine.

  (2) In the above embodiment, six fan-shaped resonance prevention holes 70 are provided in the web portion 60. However, the present invention is not limited to the resonance prevention holes 70 having a fan shape. Alternatively, the shape may be a circle, an ellipse, a triangle, a polygon, or other various shapes. However, it is necessary to provide a plurality of resonance prevention holes 70 in a state where the center of gravity of the molded plastic gear 30 is not displaced. Further, the number of resonance prevention holes 70 is not limited to six, and an appropriate number may be set according to the situation.

  (3) In the present embodiment, the width dimension W1 of the tooth portion 40 is set to be the same as the width dimension W2 of the shaft portion 50. However, the width dimension W1 is limited to the same width dimension. Instead, the width dimension W2 of the shaft part 50 may be made smaller than the width dimension W1 of the tooth part 40 or vice versa depending on the application and situation.

  (4) In the above embodiment, one or more rims are provided concentrically on the web portion 60, and the anti-resonance holes 70 are formed in the web portion 60 between the rim and the tooth portion 40 and between the rim and the shaft portion 50. May be provided. When there are a plurality of rims, the anti-resonance hole 70 can be provided in the web portion 60 between the rims.

It is explanatory drawing of front sectional view for demonstrating the outline | summary of the printer with which the shaping | molding plastic gear concerning this invention is applied. It is a perspective view showing one embodiment of a drive unit which transmits power to various devices in a printer. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows one Embodiment of the shaping | molding plastic gear concerning this invention, (A) is a perspective view, (B) is the sectional view on the AA line of (A). FIG. 6 is a circular graph showing an example of dimensional accuracy of a molded plastic gear having a resonance prevention hole, wherein (a) shows a method of manufacturing a molded plastic gear according to the present invention (after the basic gear is manufactured by a molding process, the resonance prevention hole is drilled; The measurement results of the diameter dimensions of the molded plastic gears manufactured by the two-stage system that performs the setting process (Example), (b) are manufactured in one stage using a mold having a core for resonance prevention holes. The measurement results (comparative examples) of the diameter dimensions of the molded plastic gears are shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Printer 11 Housing | casing 111 Paper conveyance path 112 Registration roller pair 113 Transfer roller 114 Paper discharge conveyance path 115 Paper discharge tray 12 Image forming unit 12C Cyan unit 12K Black unit 12M Magenta unit 12Y Yellow unit 121 Photosensitive drum 121a Drum shaft 122 Developing device 122a Toner cartridge 123 Charger 124 Exposure device 125 Transfer belt 125a Drive roller 125b Driven roller 126 Transfer roller 127 Cleaning device 13 Fixing unit 131 Heating roller 132 Pressure member 133 Pressure roller 134 Pressure belt 14 Paper storage Portion 141 Paper tray 142 Pickup roller 15 Drive unit frame 20 Drive unit 21 Drive motor 211 Drive shaft 22 Idle shaft 23 First shaft 24 Second shaft 25 Third shaft 30 Molded plastic gear 31 Drive gear 32 Idle gear 33 Large diameter gear 34 Small diameter gear 35 Small diameter gear 35 Medium diameter gear 36 Medium diameter gear 40 Tooth portion 41 Tooth 50 Shaft portion 51 Shaft hole 60 Web portion 70 Resonance prevention Hole P paper

Claims (3)

Prevents resonance with vibration caused by driving of the driving source in the web portion of the basic gear having an annular web portion used for transmitting driving force from the driving source in various devices incorporated in the image forming apparatus. A method of manufacturing a molded plastic gear provided with a resonance prevention hole as much as possible,
A basic gear molding step of molding a basic gear by injecting and injecting a synthetic resin raw material heated and melted into a mold having a cavity corresponding to the external shape of the web portion in a state where the resonance prevention hole is not provided;
A method for producing a molded plastic gear, wherein a molded plastic gear is manufactured through a resonance prevention hole drilling step of drilling a resonance prevention hole in the web portion of the basic gear.   2. The method of manufacturing a molded plastic gear according to claim 1, wherein the resonance preventing hole is shaped so that the center of gravity of the molded plastic gear does not shift from the center of gravity of the basic gear.   3. The method of manufacturing a molded plastic gear according to claim 1, wherein three or more resonance preventing holes are formed.

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