JP4461212B2 - Micro gear - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a micro-internal gear having a very small diameter used in a micromachine or the like.
[0002]
[Prior art and problems]
Research on micromachines has become active, and ultra-small servo drive mechanisms that drive very small machines are required. When pursuing miniaturization of the servo drive mechanism, a large motor is required when directly driving by a motor alone. However, a combination of a small motor and a gear reducer is advantageous because it is smaller. This is because the power transmission force of the gear is much larger than the electromagnetic force of the motor, so that the reduction gear can transmit a large torque even if it is small. For this reason, the gear reducer has played a major role in downsizing the drive mechanism.
[0003]
Among the gear reducers, the planetary gear mechanism reducer is the most compact and has been downsized to an outer diameter of 10 mm. The planetary gear mechanism has a high space efficiency because it uses a plurality of planetary gears, and is the most compact and lightweight among the gear mechanisms. In addition, since the load is shared among the plurality of planetary gears and the tooth shape of the internal gear is concave, the tooth surface contact stress can be lowered by meshing with the non-planetary gear, so that a large torque can be transmitted. In addition, since the input shaft and the output shaft are coaxial, the motor and the load can be connected in a compact manner.
[0004]
However, an ultra-compact planetary gear reducer, for example, a fine gear with a module of 0.1 or less is required when the outer diameter is 10 mm or less. In the conventional gear cutting method, the standard bob for generating an involute spur gear has the smallest module 0.1. Therefore, there is a wire electric discharge machining method as a machining method that can cope with the gears of the micromodule. A ready-made wire can be used as an electrode corresponding to a tool, and when this is applied to gear processing, a single type of wire can be used for a wide range of modules. Since an extra fine wire can be used, it is expected as a processing method of a micro gear.
[0005]
However, when the micro gear is further reduced in size, there is a limit to the reduction in size due to the restriction of the wire diameter. In particular, since R of the wire diameter of wire electric discharge machining is a trace, as shown in FIG. 3, the actual root circle diameter dr2 may be smaller than the theoretical root circle diameter dr1, or as shown in FIG. In addition, there is a drawback that a round-down occurs and a smooth involute curve is not obtained.
[0006]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a micro gear that is smaller in size so as not to cause a round-down that forms a non-smooth part in an involute curve that should form a gear tooth profile if a wire with a minimum diameter is used. . Further, when processing the same module gear, the wire diameter can be increased, so that the connection work is easy and the yield due to wire breakage or the like is improved.
[0007]
[Means for Solving the Problems]
The present invention has been made to solve the above-mentioned conventional drawbacks. In the microgear according to claim 1 of the present invention, teeth protruded at a constant interval from the inner peripheral portion manufactured by wire electric discharge machining. The tooth profile corresponding to the tooth surface and the tooth bottom surface consisting of the tooth end surface and the tooth root surface has an involute curve corresponding to at least a part of the tooth surface and the tooth bottom surface. the corresponding arc-shaped curved line, and is formed by an arc curve which is a part of a circle in contact with the circular arc curve corresponding to the involute curve and the tooth bottom.
[0008]
In the micro gear according to claim 2 of the present invention, in the micro internal gear according to claim 1, the wire diameter of the electric discharge machine is dw, the discharge gap is t, and the radius of the root is Rc. These are the following formulas:
Rc = (dw / 2) + t
The shape satisfying the above relationship.
[0009]
[Action]
In the microgear of the present invention, since the involute curve and the root circle in contact with the root diameter are connected by a curve having a predetermined radius R, the shape has a corrected involute curve. Does not become smaller than the theoretical root diameter, or does not cause a cut-off that forms a non-smooth part in the tooth profile.
[0010]
【Example】
The present invention will be described below with reference to illustrated embodiments. FIG. 1 is a view for explaining a micro gear according to an embodiment of the present invention, and FIG. 2 is a view for explaining electric discharge machining according to the present invention.
[0011]
Hereinafter, the micro gear of the present embodiment will be described with reference to FIGS. In wire electric discharge machining of gears, a virtual tool (diameter ds) with a circular cross section is moved by the NC device along the involute tooth profile curve (in actual machining, the wire position is fixed and the workpiece is moved by the NC device. ) Thus, since a wire or a workpiece | work is moved with NC apparatus, it can respond to a wide range of modules.
[0012]
However, when the tooth gap width of the machining gear is narrower than the virtual tool diameter, the machining has been limited by the tool interfering with the adjacent involute and causing undercutting. When the diameter is dw, the discharge gap is t, and the root radius is Rc,
Rc = (dw / 2) + t
The curve having a modified involute curve formed by connecting the curve (the tooth profile corresponding to the tooth bottom surface) that meets the above relationship and the involute curve with the curve of the radius R that is the tangent of both curves is used. The actual root circle diameter became smaller than the theoretical root circle diameter, and no rounding occurred.
In other words, the involute tooth profile curve may be cut down to a non-smooth portion in the normal case, but when wire electric discharge machining is performed so that the tooth profile has the modified involute curve shape, There is no devaluation beyond the intended shape.
[0013]
【The invention's effect】
As is clear from the above description, according to the present invention, if a wire having a minimum diameter is used, a further small microgear can be provided as long as no lowering occurs. Moreover, when processing the gear of the same module, since a wire diameter can be enlarged, it is easy to perform a connection work and it is possible to improve the yield due to wire breakage or the like.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a micro gear according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating electric discharge machining according to an embodiment of the present invention.
FIG. 3 is a diagram for explaining electric discharge machining of a conventional example.
FIG. 4 is a diagram for explaining electric discharge machining of a conventional example.
[Explanation of symbols]
Ra, Rb Pseudo involute curve radius Rd Predetermined radius R
Rc root radius R
dw Wire diameter t Discharge gap dk Tip circle diameter dr1 Theoretical root circle diameter dr2 The actual root circle diameter

Claims (2)

In a micro internal gear having teeth protruding at a constant interval on the inner periphery manufactured by wire electric discharge machining,
The tooth profile corresponding to the tooth surface and the tooth bottom surface consisting of the end surface and the root surface,
An involute curve corresponding to at least part of the surface of the addendum,
An arc curve corresponding to the root surface,
A micro-internal gear formed by an arc curve that is a part of a circle in contact with the involute curve and an arc curve corresponding to the tooth bottom surface. 2. The micro internal gear according to claim 1, wherein the wire diameter of the electric discharge machine is dw, the discharge gap is t, and the radius of the root is Rc, which are expressed by the following formulas:
Rc = (dw / 2) + t
Micro internal gear characterized by satisfying the relationship of

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