JP2539323Y2 - Home search device - Google Patents

Description

[Detailed description of the invention] <Industrial application field> This invention relates to an origin finding device, and in particular, determines a specific rotation phase of a driven gear rotated by a drive gear as an origin, and automatically sets the driven gear to the origin position. The present invention relates to an origin search device that stops the operation.

<Background Art> As a conventional home search device, there is one that performs home search of a driven gear by step-out of a step motor or the like. In this device, the rotation of the driven gear is regulated by the rotation phase of the origin, and the motor loses synchronism. However, according to this device, there is a disadvantage in terms of durability because the motor noise at the time of step-out is large and the motor load at the time of origin search is large.

Accordingly, the present applicant has previously filed a Japanese Patent Application No. Sho 62-782 for a device for performing origin search without step-out of a motor or the like. One embodiment of the present invention is shown in FIG. In this example, while the driven gear 62 is formed with the toothless portion 116 to which the rotation of the drive gear 64 is not transmitted,
The toothless portion 116 is formed corresponding to the origin, and the driven gear 62
A leaf spring 150 is fixed in a cantilevered state in the recess 124. The leaf spring 150 abuts against the stopper 128 and is elastically deformed immediately before the meshing of the teeth corresponding to the toothless portion 116 of the driven gear 62 is canceled by the rotation of the drive gear 64 in the direction A in the drawing. The idle rotation of the drive gear 64 is allowed while allowing the minute rotation of the driven gear 62 within the elastic limit. As a result, the driven gear 62 can be maintained at the home position. If the rotation of the drive gear 64 is stopped in this state, the driven gear 62 is necessarily positioned at the home position. The origin search of the driven gear 64 is automatically performed.

<Problems to be Solved by the Invention> The above-mentioned origin finding device allows the driving gear 64 to idle due to the elastic force of the leaf spring 150 and the driven gear
62 is maintained at the home position, but the elastic deformation capacity (the amount that can be elastically deformed without causing plastic deformation or destruction) enough to allow idling of the drive gear 64 and the driven gear 62
The leaf spring 150 is required to have an elastic force large enough to reversely rotate the driven gear 62 at the moment when the engagement with the drive gear 64 is disengaged and bring the driven gear 62 into engagement with the drive gear 64 again. However, if the elastic deformability and elastic force of the leaf spring 150 are set to be large, the tooth 152 located at one end of the toothless portion 116 of the driven gear 62
When the teeth of the drive gear 64 come into contact with (hereinafter, referred to as specific teeth) and the driven gear 62 idles while rotating with a small angle against the elastic force of the leaf spring 150, when the teeth are disengaged from each other, The driven gear 62 is suddenly returned in the opposite direction by the elastic force of the spring 150, and the specific tooth 152 collides with the next tooth of the drive gear 64,
At that time, there is a problem that unpleasant noise is generated.

<Means for Solving the Problems> The present invention has been made to solve this problem, and as described above, the forward direction of a driven gear rotated in both forward and reverse directions by a drive gear. In the home search device that performs home search of the driven gear by controlling the rotation of the driven gear at the home position by the rotation control device, the rotation control device includes a non-rotating first restricting member provided in close proximity to the driven gear; A second regulating member provided on the gear so as to rotate with the driven gear and engaging the first regulating member to regulate the rotation of the driven gear in the forward direction. At least one of the members is allowed to rotate within a limited angle range of the driven gear by elastically deforming, and the toothless region where the rotation of the driving gear is not transmitted to the driven gear. And forming a specific tooth adjacent to one end of the missing tooth region on the specific tooth elastic support device, and the specific tooth elastic support device,
When the rotation of the driven gear is restricted by the rotation restricting device, the relative rotation of the driven gear with respect to the driven gear is allowed by allowing the specific teeth engaged with the driving gear to enter the center side of the driven gear by its own elastic deformation. While the drive gear includes an elastic member for returning the specific teeth to the original position when the driven gear rotates the driven gear in the reverse direction.

<Operation> In the origin finding device according to the present invention, at the origin position of the driven gear, the rotation restricting device allows a small angle rotation of the driven gear by elastic deformation of at least one of the first and second restricting members, but more than that. In a state where the rotation of the driven gear is prevented and the rotation of the driven gear is prevented by the rotation restricting device, the specific tooth elastic support device allows the specific tooth to be immersed, thereby allowing the drive gear to rotate at a small angle. That is, each time the teeth of the drive gear pass, the driven gear rotates in the small angle positive direction, and the specific teeth elastically supported by the specific tooth elastic support device are:
The elastic member of the specific tooth elastic supporting device is elastically deformed and immerses into the center side of the driven gear, thereby allowing each tooth of the drive gear to pass over the specific tooth of the driven gear. In this way, the rotation of the drive gear at the origin is allowed by both the elastic deformation of at least one of the first and second regulating members and the elastic deformation of the elastic member of the specific tooth elastic support device, whereby the aforementioned FIG. The elastic deformation of the regulating member can be smaller than that of the conventional device, which is permitted only by the elastic deformation of the regulating member (leaf spring 150) of the rotation regulating device. In this case, the elastic deformation of the elastic member of the specific tooth elastic supporting device can be reduced as compared with the case where the rotation of the driving gear is permitted only by the specific tooth immersion permission.

In addition, it is not necessary or possible to form a relief for preventing the specific tooth from cutting into the root of the drive gear. If the rotation restricting device does not permit the rotation of the driven gear at the origin, and the rotation of the driving gear is permitted only by the retraction of the specific tooth by the specific tooth elastic support device, immediately after the tooth of the driving gear comes off the specific tooth In addition, the specific tooth may move substantially in the radial direction of the driven gear, and the edge of the tip surface of the specific tooth may collide with the root of the tooth just released from the drive gear. At this time, since the angle between the moving direction of the edge of the specific tooth and the tooth surface of the root portion of the drive gear is small, the edge of the specific tooth bites into the tooth surface of the tooth root due to the wedge effect, and the drive is performed. It may cause gear damage or abnormal wear. Therefore, in order to avoid the occurrence of such a situation, it is necessary to cut off a portion of the specific tooth which may bite into the root portion of the drive gear tooth to form a relief. In, the regulating member of the rotation regulating device is made elastically deformable, and when the specific teeth of the driven gear are disengaged from the teeth of the driving gear, the driven gear is reversely rotated by the elastic force of the regulating member. In addition, the moving direction of the specific tooth includes, in addition to the substantially radial component based on the elastic force of the specific tooth elastic support device, the circumferential component accompanying the reverse rotation of the driven gear, the occurrence of the bite is completely prevented. It is avoided or the likelihood of digging is reduced. As a result, the escape of a specific tooth becomes unnecessary or small.

<Effect of the Invention> As described above, the rotation of the drive gear at the origin is permitted by both the elastic deformation of the restricting member and the elastic deformation of the elastic member of the specific tooth elastic support device, so that the restricting member is elastically deformable. Since the elastic deformation ability of the elastic member of the specific tooth elastic support device and the elastic member of the specific tooth elastic support device can be small, the elastic member of the elastic member of the specific tooth elastic support device and the elastic member of the specific tooth elastic support device can be reduced. Can be easily reduced in size. Alternatively, if the size of the elastically deformable regulating member and the elastic member of the specific tooth elastic support device are the same, the amount of elastic deformation can be small, so that the life of the elastic member is prolonged, and the durability of the home search device is reduced. The effect of improving the performance is obtained.

Also, compared to the case where the rotation of the drive gear at the origin is permitted only by the rotation of the driven gear accompanying the elastic deformation of the regulating member, the reverse rotation angle of the driven gear when the mesh is released is reduced, and the reverse rotation speed is reduced. Since the moving direction of the specific tooth due to the elastic force of the elastic member of the specific tooth elastic support device is substantially radial, the specific tooth and the driving gear can be re-engaged when the driving gear and the driven gear are engaged again. The effect of reducing the collision speed with the teeth and reducing the noise generated at the time of meshing can be obtained.

In addition, as described above, the escape of the specific tooth becomes unnecessary or small, so that when the drive gear is rotated reversely after the home search, the drive gear and the driven gear can smoothly mesh with each other. It also has the effect of starting. The fact that the relief is formed in the specific tooth is the same as the fact that the backlash at the start of the reverse rotation of the drive gear and the driven gear is extremely large, so that the meshing does not start smoothly, causing noise generation. It will be,
If the escape is small or no longer necessary, the start of engagement at the start of reverse rotation is performed smoothly, and the generation of noise is favorably suppressed.

<Embodiment> An embodiment in which the present invention is applied to a head drive cam origin finding device in a thermal printer will be described below with reference to the drawings.

FIG. 4 is an external view of an electronic typewriter provided with the thermal printer 2. A keyboard 4 is integrated with the thermal printer 2, and the keyboard 4 is provided with various keys such as alphabet keys 6 and a liquid crystal display 8 having a predetermined number of digits, and displays characters, symbols, and the like input by keys. It is supposed to be. Printing is performed by the thermal printer 2 based on the data input from the keyboard 4.

The thermal printer 2 has a carriage 10. The carriage 10 is moved X along the platen 14 by the guide bar 12.
It is supported movably in the axial direction, and is driven by a carriage drive motor provided on the printer frame 16 (not shown). A paper feed roller (not shown) is provided behind the platen 14, and is driven by a roller drive motor (not shown) provided on the frame 16 to feed the printing paper 20 in the Y-axis direction.

Thermal head as print head on carriage 10
22 is held, and the printing paper 20
Supplied between 22 and platen 14. Also carriage 10
A ribbon cassette 24 is detachably mounted on the top, from which an ink ribbon 26 is attached to the thermal head 22 and the printing paper 20.
Is managed between. When the thermal head 22 is pressed against the printing paper 20 via the ink ribbon 26, the ink on the ink ribbon 26 is transferred to the printing paper 20 by heat.

FIG. 3 is an exploded view of the carriage 10 and a mechanism installed therein. The carriage 10 includes a bar insertion portion 28, into which the guide bar 12 is inserted. This carriage 10
At the top, the head drive unit 30 and the ribbon winding unit 32 are assembled in a sub-assembly state, respectively.
The units 30 and 32 are mounted on the carriage 10.

The head drive unit 30 includes a unit frame 34,
A head lever 36 for printing and a collection lever 38 for erasing are supported on the frame 34 so as to be independently rotatable about the same axis of a shaft 40 in a horizontal plane. The thermal head 22 is integrally formed at the tip of the head lever 36. A head substrate 43 in which a plurality of heating elements 42 are linearly arranged is attached to a printing surface of the thermal head 22, that is, a front surface, and a power supply cable 44 and a printed wiring (not shown) formed on the surface of the head substrate 43. Thus, each heating element 42 is energized.

The head lever 36 has an intermediate portion serving as a rotation fulcrum (40). The end of the head lever 36 opposite to the thermal head 22 with respect to the shaft 40 is a cam follower via a head pressing spring 46. It is connected to a cam lever 48.
The cam lever 48 is rotatably supported in a vertical plane by a lever shaft 50 provided on the unit frame 34, and has integral arms 52 and 54 extending to both sides from the lever shaft 50 as apparent from FIG. Have. The head pressing spring 46 is a tension coil spring, and is a so-called close contact spring, which is brought into close contact by applying a predetermined compression preload, and does not elastically deform unless a load exceeding the preload is applied. This spring 46 is provided between the rear end of the head lever 36 and the cam lever 48.
Of the arm 52. The arm 54 of the cam lever 48 comes into contact with a head drive cam 58 as a first cam via a roller 56.

The head drive cam 58 is a cam shaft parallel to the lever shaft 50.
The cam 58 is rotatably supported by the unit frame 34 via a gear 60. A gear 62 is concentrically fixed to the cam 58, and the gear 62 is engaged with a cam drive gear 64.
The cam drive gear 64 is a gear drive shaft with two circular shafts
The gear 64 is fitted in the unit frame 34 so as to be relatively non-rotatable and slidable in the axial direction. As shown in FIG. Is regulated, and moves together with the carriage 10.

The gear drive shaft 66 is inserted into the gear 64 through circular shaft holes 68 and 70 formed on both side walls of the carriage 10 and similar shaft holes 72 formed in the unit frame 34. Then, as shown in FIG.
, Is rotatably supported by a printer frame 16 and is connected to a head drive motor 74 provided on the frame 16 via a gear. Therefore, this motor
When the shaft 66 is rotated by 74, the rotation is transmitted to the head drive cam 58 via the gears 64 and 62 shown in FIG.

The cam 58 has a first cam surface 80, a second cam surface 82, and a third cam surface 84 on the left side as shown in FIG. The first cam surface 80 is a cam surface with a steep gradient, which rises sharply from the base cylindrical surface 86 constituting the base circle, and the cam lever 48 has a large lift amount, It provides a dynamic motion and is continuous with the second cam surface 82. The second cam surface 82 is the first cam surface 80
A cam surface having a gentler gradient, the distance from the rotation center of the cam 58 is formed along a curve that gradually increases with the rotation of the cam 58, and the lift amount of the first cam surface 80 is, for example, 1/2 to 1 / Three
And is continuous with the third cam surface 84. The third cam surface 84 is formed along an arc centered on the rotation center of the cam 58, and the lift amount in this region is zero.

The first cam surface 80 is located in the entire cam surface and functions as a head stroke area corresponding to a stroke process from the release position of the thermal head 22 to the printing position. It functions as a head pressing area corresponding to a pressing process on the printing paper 26 and the printing paper 20. The third cam surface 84 can be said to be a head pressing stable area for stably maintaining the pressing state of the thermal head 22, and the basic cylindrical surface 86 having an absolutely zero lift amount moves the thermal head 22 to the release position. It can be said that the head release stable region is maintained stably.

A first cam surface 90, a second cam surface 92, and a third cam surface 94 are formed symmetrically to the left side on the right side of the cam 58, and the third cam surface 94 and the third cam surface 84 are connected to each other. Are continuous on the center line. Therefore, this cam 58
7, the cam lever 48 is rotated similarly in the case of rotating in the counterclockwise direction and the case of rotating in the clockwise direction.

As apparent from FIG. 5, a head return spring 96 is stretched between the head lever 36 and the unit frame 34 with a predetermined tensile preload, and the head lever 36 is moved in a direction in which the thermal head 22 is released. It is energizing. The thermal head 22 is stably held at the release position by the urging force of the head return spring 96. This head return spring 96 causes the head lever 36 to generate a rotational moment about the shaft 40 in the opposite direction to the head pressing spring 46. However, if the lengths of the arms of both rotational moments are the same, the head return spring 96 is used. The spring 96 is a spring that is weaker than the head pressing spring 46, and as shown in FIG. 6, the maximum load when the thermal head 22 is fully extended corresponding to the printing position is the head pressing spring 46.
(Adhesion spring) is set to be equal to or less than the set preload. Therefore, the thermal head 22 is
During the stroke process up to the printing position against the urging force, the head pressing spring 46 does not elastically deform, and functions similarly to the rigid link.

Returning to FIG. 3, a collection blade 98 is fixed to the tip of the collection lever 38. The collection blade 98 is located at a small distance in the longitudinal direction of the platen 14 from the thermal head 22. The collection blade 98 has an operation position in which the collection blade 98 comes into contact with the printing paper 20 via the ink ribbon 26 and a release position (retreat position) which is separated from the printing paper 20. At the same time, it is movably supported by a collection lever 38. When the collection blade 98 is pressed against the printing paper 20 via the ink ribbon 26 together with the thermal head 22, the ink once transferred to the printing paper 20 adheres to the ink ribbon 26 and erases and corrects the printed portion. Becomes possible. That is, the ink of the ink ribbon 26 cools during the time of traveling between the head 22 and the collection blade 98 to reach the intermediate temperature, and the adhesive force is generated in the intermediate temperature range.

The collection lever 38 is driven by the same mechanism as the head lever 36 and has a common drive source, and is connected to a cam lever 102 as a second displacement member via a blade pressing spring 100. The blade pressing spring 100 is also a so-called close contact spring that is brought into close contact with a constant compression preload, and a blade return spring 104 that is weaker than this spring 100 is stretched between the collection lever 38 and the unit frame 34, and the collection blade 98 is moved. It is urging in the release direction. The cam lever 102 is rotatable independently of the lever 48 by the same shaft 50 as the cam lever 48 described above.
08 is engaged.

As is apparent from FIG. 8, the cam 108 has the first cam surface 100 and the first cam surface 1
The second cam surface 112, which has a gentler gradient than this, continuously from 10,
And a third cam surface 114 formed along an arc centered on the rotation center of the cam 108 following the second cam surface 112. The base cylindrical surface 86 is a release stable area of the collection blade 98, and the first cam surface 110 is a blade stroke area for bringing the collection blade 98 from the release position to the operating position. The second cam surface 112 further moves the collection blade 98 in the operation position and further
The third cam surface 114 is a blade pressing area for pressing
Is a pressure stable region of the collection blade 98.

Such a blade drive cam 108 is a head drive cam 5
8 are concentrically fixed on the same camshaft 60, and their cam surfaces 110, 112, 114 correspond to the cam surfaces 90, 92, 94 of the head drive cam 58. The phases are shifted. That is, as shown in FIG. 9, the cam surfaces 110 and 112 of the blade drive cam 108 and the cam surfaces 90 and 92 of the head drive cam 58 do not overlap each other. 108 and 58 are integrated and can be rotated synchronously. In this embodiment, in the clockwise direction in FIG. 9, the cam surface 110 and the like of the blade drive cam 108 precede the cam surface 90 and the like of the head drive cam 58. Therefore, at the time of the clockwise rotation, the collection blade 98 starts approaching and pressing on the printing paper 20 before the thermal head 22 in time. By the way, by moving the thermal head 22 first and holding the ink ribbon 26 between the printing paper 20 and the collection blade 98
Is moved, the ink ribbon 26 which has been used for printing and has already been taken up tends to be pulled out. This movement is prevented in the order of the present embodiment. The motor 74 shown in FIG.
And 108 are common driving sources.

The origins of the head driving cam 58 and the blade driving cam 108 as described above are determined by an origin finding device as shown in FIG. Here, the gear 62 fixed to the head drive cam 58 and the like functions as a driven gear, and the gear 64 connected to the motor 74 via the shaft 66 functions as a drive gear.

In the gear 62, a toothless region 116 having a smooth cylindrical surface formed by removing, for example, about two or three teeth is formed in a part in the circumferential direction. The missing tooth region 116 is defined by setting the intermediate point of the head pressing stable region of the head driving cam 58 shown in FIG.
It is formed corresponding to the origin O. That is, the origin O
When the roller 56 (see FIG. 5) is engaged with the
6 (more precisely, one end thereof) has a phase relationship corresponding to the gear 64.

As shown in FIGS. 1 and 2, a notch 121 is formed between a tooth 118 (referred to as a specific tooth) located at one end of the toothless region 116 of the driven gear 62 and an adjacent tooth 120 thereof. . This notch 121 is cut into the center of the gear 62 once from the bottom of the tooth space between both teeth 118 and 120,
Extends along 116. As a result of the formation of the notch 121, a thin arm-shaped meat portion (12
2) is left, and this portion is an arm-shaped spring portion 122 integrated with the main body of the gear 62. That is, the specific tooth 118 is formed integrally with the free end of the arm-shaped spring portion 122, and the specific tooth 1 is formed by the elastic force of the arm-shaped spring portion 122.
The support 18 is elastically displaceable in a direction away from or near the center of the drive gear 64. In the present invention, the arm-shaped spring portion 122 for elastically supporting the specific teeth 118 functions as a specific tooth elastic support device and an elastic member thereof. That is, the arm-shaped spring portion 122, which is an elastic member, independently constitutes the specific tooth elastic support device.

In some cases, the specific teeth 118 need to form a relief as illustrated by a broken line in FIG. 2, but in this embodiment, no relief is formed as shown by a solid line, and the driven gear 62 It has the same tooth shape as other teeth (120 etc.). The need for escape will be described later.

The driven gear 62 has a smooth recess 124 on the end face on the unit frame 34 side, and a leaf spring 130 is provided in the recess 124, while a stopper 128 is provided on the unit frame 34. In this example, the leaf spring 130 is provided inside the driven gear 62 corresponding to the missing tooth region 116. on the other hand,
The stopper 128 has a short axis shape, is fixed at a position where it can be engaged with the leaf spring 130 in the unit frame 34, and protrudes into the recess 124 of the gear 62. In the rotation process of the driven gear 62 in the clockwise direction in FIG. 1, the rotation of the driven gear 62 is prevented by the leaf spring 130 abutting on the stopper 128. As shown in the figure, a state is established in which the specific gear 118 of the driven gear 62 is engaged. In other words, the leaf spring 130 and the stopper 1 are brought into such a state.
The relative positional relationship with 28 has been determined. The stop phase of the driven gear 62 is the rotation phase of the origin (hereinafter referred to as the origin phase). In the present embodiment, the stopper 128 is
Together with 30, a rotation restricting device that restricts the rotation of the driven gear 62 in the origin phase is configured. Stopper 128 and leaf spring 130
Function as the first and second regulating members, and the leaf spring 130, which is one of the two regulating members, is an elastically deformable regulating member.

The leaf spring 130 has a base end bent at a substantially right angle to form an L-shape, is inserted between the spring fixing portions 132, 134 and 136 at the base end, and is supported in a cantilever state extending in the radial direction of the driven gear 62. Have been. And excessive deformation prevention projection 138
This prevents the leaf spring 130 from being deformed beyond its own elastic limit. Leaf spring 130 excessive deformation prevention protrusion 1
The plate surface opposite to 38 abuts against the stopper 128, and is elastically deformed in an arc shape in a direction approaching the projection 138.
138 to prevent further elastic deformation.

Hereinafter, the operation of the home search device and the operation of the thermal printer 2 related thereto will be described.

When the thermal printer 2 is initialized, the motor 74
(In this embodiment, a step motor or a DC motor with a servo is a motor that can be stopped at a position rotated by a desired angle from the origin unless the power is turned off once the origin is given.) When the gear 64 rotates in the direction A in the figure while meshing with the driven gear 62,
During the rotation process, the driving gear 64 is engaged only with the specific teeth 118 of the driven gear 62, and the leaf spring 130 of the driven gear 62 abuts on the stopper 128 in synchronization therewith. Even after this contact, the driven gear 62 continues to rotate while the leaf spring 130 is elastically deformed, whereby the rotation of the drive gear 64 is allowed. The rotation of 62 is blocked.

On the other hand, as shown in FIG.
As the 9 rotates in the direction of the arrow while contacting the tooth surface of the specific tooth 118 of the driven gear 62 (the tooth surface on the side of the missing tooth region 116), the drive gear 64 becomes a cam and the specific tooth 118 becomes a cam follower, As the teeth 129 progress, the specific teeth 118 are
2 immerses in the center side of the driven gear 62 based on the elastic deformation of
The passage of the tooth 129 (that is, over the specific tooth 118) is permitted.

Condition 12 in which both teeth 118 and 129 are engaged with each other on the tip surfaces
When the step 9 further proceeds, the specific tooth 118 is rapidly moved toward the base of the tooth 129 by the restoring force of the arm-shaped spring section 122. As a result, if the edge of the cutting edge of the specific tooth 118 collides with the tooth surface of the tooth root of the tooth 129, the tooth surface of the tooth root may be damaged or abnormally worn. The specific tooth 118 is suddenly moved almost radially by the restoring force of the arm-shaped spring portion 122 at the moment when the specific tooth 118 is disengaged from the tooth 129, and the angle formed by this moving direction and the tooth surface of the tooth 129 at the root portion Because is small, the edge of the specific tooth 118 will bite into the tooth surface of the root of the tooth 129 due to the wedge effect,
The bite may cause damage or abnormal wear on the tooth surface of the root portion of the tooth 129.

To prevent this damage or abnormal wear,
As indicated by a broken line in the figure, it is effective to cut off the vicinity of the edge of the specific tooth 118 that may bite into the tooth surface of the root portion of the tooth 129 to form a relief.

However, in the present embodiment, if the specific tooth 118 is disengaged from the tooth 129, the driven gear 62 is rotated in the opposite direction by the restoring force of the leaf spring 130, so that the moving direction of the specific tooth 118 is A substantially radial component due to the restoring force of the arm-shaped spring portion 122 and the driven gear 62 due to the restoring force of the leaf spring 130.
And a component in the circumferential direction based on the rotation of the specific tooth 118, and the bite of the edge of the specific tooth 118 into the tooth surface of the root portion of the tooth 129 is less likely to occur than in the case of only the component in the radial direction. In the present embodiment, in particular, the elastic characteristic of the leaf spring 130 is set to such a size that there is no risk of biting, so that the specific teeth 118 do not have relief as described above.

As long as the drive gear 64 continues to rotate in the direction A, as described above, the driven gear 62 with elastic deformation and restoration of the leaf spring 130 is used.
Of the drive gear 64 and the specific teeth 118 of the driven gear 62 by the reciprocal rotation of
Is repeatedly permitted, and the driven gear 62 is kept at the origin phase. At this time, since the leaf spring 130 does not need to independently allow the tooth 129 to climb over the specific tooth 118, the amount of elastic deformation can be reduced, and the reverse rotation of the driven gear 64 when the tooth 129 comes off from the specific tooth 118. The amount is small. Further, since the moving direction of the specific tooth 118 accompanying the restoration of the arm-shaped spring portion 122 is almost radial, the relative speed when the specific tooth 118 collides with the next tooth 129 can be small, and the generated noise is small. I can do it.

The drive gear 64 always rotates in the direction A regardless of the predetermined rotation amount, that is, regardless of the phase of the driven gear 62.
After rotating 116 by a rotation amount that can correspond to drive gear 64, it is stopped by control of motor 74. At this time specific teeth
Numeral 118 is maintained in contact with an arbitrary tooth 129 of the drive gear 64 based on the elastic force of the arm-shaped spring portion 122 and the elastic force of the leaf spring 130. This is an origin finding state. At this time, the roller 56 of the cam lever 48 shown in FIG. 5 is in a state of riding on the origin O on the head pressing stable area in FIG.

Thereafter, the drive gear of FIG.
64 rotates in the C direction.
Since 118 is pressed against the teeth 129 of the drive gear 64 by the elastic force of the leaf spring 130, the driven gear 62 starts to rotate at the same time as the drive gear 64 starts to rotate. At this time, if specific teeth 118
If the elastic force of the leaf spring 130 is extinguished, the tooth behind the tooth 129 (in the direction C) which has been engaged with the specific tooth 118 until then is lost. The driven gear 62 engages the formed surface, or until a further tooth 129 engages an adjacent tooth 120 adjacent to the particular tooth 118.
Does not rotate, and the rotation transmission state becomes the same as that of normal gears only after any engagement. That is, when the relief is formed in the specific tooth 118, the backlash between the drive gear 64 and the driven gear 62 is large at the start of the rotation in the C direction, and the rotation of the drive gear 64 is driven. Gear 62
Does not follow smoothly and generates noise. However, in the present embodiment, as described above, since no relief is formed in the specific teeth 118, the driven gear 62 smoothly follows the rotation of the drive gear 64 from the start of rotation, and noise is favorably generated. Be avoided.

The drive gear 64 is stopped after rotating the driven gear 62 by approximately 180 degrees, so that both the roller 56 of the cam lever 48 and the roller 106 of the cam lever 102 correspond to the basic cylindrical surface 86 shown in FIG. , Thermal head 22
The collection blade 98 and the collection blade 98 are both kept in a released state.

Another embodiment of the present invention is shown in FIG. This example is
The specific teeth 140 are provided separately from the driven gear 62, and are elastically supported by a compression coil spring 142 as elastic support means for specific teeth. A concave portion 144 is formed in the body width direction of the driven gear 62 holding the specific tooth 140, and the specific tooth 140 is provided so as to be able to protrude by a limited amount in a state where the lower half is accommodated in the concave portion 144. And is constantly urged in the protruding direction by the compression coil spring 142 arranged in a pre-compressed state. When the drive gear 64 idles, the driven gear 62 repeats reciprocating rotation at a certain angle and the specific teeth 14
When 0 repeats immersion and projection, an effect similar or substantially similar to that of the above-described embodiment can be obtained.

In addition, it is needless to say that the present invention can be carried out in various modified and improved modes based on the knowledge of those skilled in the art.

[Brief description of the drawings]

FIG. 1 is a perspective view of an origin finding apparatus according to an embodiment of the present invention, and FIG. 2 is an enlarged view showing a main part thereof. FIG. 3 is an exploded perspective view of a carriage of the thermal printer including the above-mentioned origin finding device and a mechanism mounted thereon. FIG. 4 is a perspective view showing the appearance of an electronic typewriter including the thermal printer. FIG. 5 is a perspective view showing a released state of the head drive mechanism in FIG. 3 taken out, and FIG. 6 is a perspective view showing a pressed state of the head drive mechanism. FIG. 7 is a front view showing the outline of the head drive cam in FIG. 3, FIG. 8 is a front view showing the same outline of the blade drive cam, and FIG. 9 is a front view showing the combined state of the two cams. FIG. FIG. 10 is an enlarged view of a main part of an origin finding apparatus according to another embodiment of the present invention. FIG. 11 is a perspective view of an origin finding device, which is a background art of the present invention. 62: driven gear, 64: drive gear, 116: missing tooth region, 118: specific tooth 122: arm-shaped spring, 128: stopper, 130: leaf spring, 138:
Excessive deformation prevention projection, 140: specific tooth, 142: compression coil spring,
144: Recess

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-50-54759 (JP, A) JP-A-61-141853 (JP, U) JP-A-63-108751 (JP, U) JP-A-57- 150653 (JP, U) Jiko 60-23571 (JP, Y2) Jiko 57-19883 (JP, Y2)

Claims (3)

(57) [Scope of request for utility model registration] An origin finding device for stopping a driven gear at an origin by restricting a forward rotation of a driven gear rotated in both forward and reverse directions by a drive gear at an origin by a rotation regulating device. A regulating device, a non-rotating first regulating member provided in proximity to the driven gear, and a driven gear provided on the driven gear so as to rotate together with the driven gear and engaging with the first regulating member. And a second restricting member for restricting the rotation of the driven gear in the positive direction, and at least one of the first and second restricting members is elastically deformed to permit rotation of the driven gear within a limited angular range. And forming a toothless area where the rotation of the drive gear is not transmitted to the driven gear, and a specific tooth adjacent to one end of the toothless area is a specific tooth The specific tooth elastic support device is capable of causing the specific teeth engaged with the drive gear to enter into the center side of the driven gear while the rotation of the driven gear is restricted by the rotation restricting device. An elastic member that allows the relative rotation of the driving gear to the driven gear by allowing the driven gear to rotate in a reverse direction, while the driving gear includes a resilient member that returns the specific tooth to the original position when the driven gear rotates the driven gear in the reverse direction. An origin finding device characterized by the following. 2. A utility model wherein the second regulating member of the first and second regulating members provided on the driven gear is a resiliently deformable leaf spring, and the non-rotating first regulating member is a stopper which does not resiliently deform. 2. The origin finding device according to claim 1. 3. The origin finding device according to claim 2, wherein the driven gear is provided with an excessive deformation preventing projection for preventing excessive elastic deformation of the leaf spring.