Planetary gear transmission systems or components – Planet periphery surrounds axis of interacting gear – Wabbler transmission
Reexamination Certificate
2001-12-21
2004-04-13
Lewis, Tisha D. (Department: 3681)
Planetary gear transmission systems or components
Planet periphery surrounds axis of interacting gear
Wabbler transmission
C475S165000, C475S170000
Reexamination Certificate
active
06719658
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a support structure for a planet gear in a simple planetary gear mechanism.
2. Description of the Related Art
The simple planetary gear mechanism comprises a sun gear; a planet gear which is supported by a carrier pin that is in turn supported by a carrier and which circumscribes the sun gear; and an internal gear in which the planet gear is inscribed. The simple planetary gear mechanism is compact, capable of providing a reduction ratio, and is adapted to easily change the reduction ratio (or the speed increasing ratio) by changing the arrangement and the input and output of each component. Thus, the simple planetary gear mechanism is widely used in various applications.
In recent years, on the other hand, production lines in factories have increased in complexity to manufacture many items in the same line. Accordingly, the entire line is not powered with a single power source as in the past but a special motor with a speed reducer is placed at individual portions of the line to cope with product diversification as well as to increase the efficiency of production. In this context, attention has been given to the simple planetary gear mechanism, as a type of a speed reducer coupled to the motor, which can be made compact.
However, the presence of backlash in each gear has turned into problems in such applications as the robot arm that requires forward and reverse rotations repeatedly and precise positioning of the arm at the predetermined absolute positions. That is, there exists backlash in the gear engagement in an unavoidable manner. With an excessive backlash, such a problem may arise that a command for reverse rotation cannot be immediately reflected on the reverse rotation of an input member (e.g., a carrier) even when the sun gear has already started its reverse rotation. This may also cause the arm to be out of alignment with its stopping positions. Accordingly, for a speed reducer of this type, the reduction of backlash has been a big problem to be tackled. The most basic method for reducing backlash has been actually practiced in many fields. According to the method, a plurality of gears are prepared first which have dimensions slightly different from each other, and then a gear is selected which engages another with the least gap upon assembly. In general, since many planet gears are employed in a speed reducer and therefore not selected preferably by try and error, internal and sun gears are to be selected.
However, there is a problem in this method that requires a large quantity of stocks and significantly reduces the efficiency of assembly, thereby easily resulting in an increase in cost. That is, for the simple planetary gear mechanism, there is another problem of variations in support position of the carrier pin relative to the carrier in addition to variations in dimension of each gear (i.e., the sun gear, the planet gear, and the internal gear). Accordingly, for example, suppose that the planet gear is given a dimension smaller than its standard dimension. In this case, to obtain proper backlash by the aforementioned method, it is necessary to incorporate a sun gear having a dimension greater than its standard dimension and an internal gear having a dimension less than its standard dimension.
Furthermore, suppose that each gear has successfully engaged another with no backlash at a certain position. Even in this case, when an attempt is made to actually rotate the gears, the gears may interfere with another at other position (due to the reduced backlash) to significantly increase the resistance to rotation. This has required a try and error attempt involving tremendous time and costs in order to provide the gears with the minimized backlash for smooth rotation at any time and positions.
In this context, there have been suggested several techniques for reducing the backlash not by try and error but by a simpler method in which some thought is put into the structure of the mechanism.
Japanese Patent Laid-Open Publication No. Sho 63-6248 suggested the following method for realizing reduced backlash. According to this method, in a simple planetary gear mechanism comprising four planet gears, those facing to each other are paired and a carrier pin for one pair of planet gears is offset in the circumferential direction in a so-called scissors configuration.
Japanese Patent Laid-Open Publication No. Hei 052-40315 also suggested the following method for realizing reduced backlash. According to this method, in a simple planetary gear mechanism comprising four planet gears, those facing to each other are paired and a carrier pin for one pair of planet gears is offset in the axial direction. In addition to this, the internal gear is divided into two in the axial direction to the offset planet gears and then one side of the internal gear is twisted in the circumferential direction to form a scissors configuration. One of the carriers disposed on both sides provides an output of forward rotation and the other provides an output of reverse rotation.
Japanese Patent Laid-Open Publication No. Hei 08-61438 suggested a structure for providing reduced backlash, in which the internal gear of the simple planetary gear mechanism is formed of elastic material to provide a negative backlash caused by the engagement of the internal gear with the planet gear.
However, consider a method for reducing backlash such as by the structure disclosed in Japanese Patent Laid-Open Publication No. Sho 63-6248. This method makes it possible to positively reduce the backlash in both the forward and reverse rotations. However, the method presents a problem that the amount of transmitted torque is reduced by one-half because only two planet gears contribute to the transmission of drive at the time of forward and reverse rotations, respectively, even though the mechanism is provided with four planet gears. There is also another problem that this method has a low degree of flexibility in designing the mechanism. That is, to maintain the torque capacities of forward and reverse rotations at the same level, it is necessary to assign the same number of planet gears to each rotation. This restricts the total number of planet gears to four in practice.
In this connection, it is well known that the so-called three-point support is better than the four-point support from the viewpoint of absorbing (or permitting) the dimensional or assembling error of each gear. However, this technique employs the arrangement in which the planet gears facing to each other are paired to adjust the backlash. This arrangement also raises a problem that it is not possible to employ a structure comprising only three planet gears, the structure corresponding to the three-point support.
Similarly, consider a method for reducing backlash such as by the structure disclosed in Japanese Patent Laid-Open Publication No. Hei 05-240315. This method also presents a problem that drive can be transmitted only by two of the four planet gears and therefore the transmission torque capacity cannot be maintained at high levels. The method raises another problem that it is not possible to employ a structure with the three-point support.
In addition, consider a method for reducing backlash such as by the structure disclosed in Japanese Patent Laid-Open Publication No. Hei 08-61438. This method provides an advantage of allowing all the planet gears to contribute to both the forward and reverse rotations. Nevertheless, the method requires the formation of the internal gear of an elastic material, thus providing bad machinability and making it difficult to maintain the strength at a sufficient level.
This method presents another problem of providing disadvantageous durability caused by the internal gear deformed each time the engagement position between the internal gear and each planet gear is displaced.
SUMMARY OF THE INVENTION
The present invention was developed in view of these conventional problems. It is therefore the main object of the present invention to al
Fukaya Sueo
Haga Takashi
Hatanaka Takashi
Lewis Tisha D.
Squire Sanders & Dempsey L.L.P.
Sumitomo Heavy Industrie's, Ltd.
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