BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially sectioned view showing the general configuration of a longitudinal motion actuator embodying the present invention.
FIG. 2 is an explanatory view for explaining the relative positional relationship between a pinion and a gear.
FIG. 3A is an explanatory view for explaining power transmission in accordance with the present invention, and FIG. 3B is an explanatory view for explaining power transmission in accordance with a conventional art, being shown for comparison.
FIG. 4 is a schematic view showing the configuration of a conventional longitudinal motion actuator.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described based on an example. FIG. 1 is a partially sectioned view showing the general configuration of a longitudinal motion actuator embodying the present invention. A motor itself shown in FIG. 1 is an ordinary one, and has a motor housing that is configured by fitting a case lid in the opening of a bottomed cylindrical motor case. In the motor housing, a stator and a rotor are housed. The shaft of the rotor is rotatably supported by bearings provided in the center of the bottom surface of the motor case and in the center of the motor lid. From the motor lid, a pair of motor terminals extend. By supplying electric power from the paired motor terminals, the motor is rotated.
The motor shown in FIG. 1 is fixed on a frame. From the center of the bottom part of the motor case, one end of the rotor shaft extends to the outside of motor through the end part of the frame as a motor output shaft, and a pinion is fixed on the motor output shaft by press fit etc.
On the other hand, first and second lead screws having the same configuration each are threaded in a spiral form excluding both end parts thereof. At one end of each of the first and second lead screws, first and second gears having the same configuration are fixed, respectively, by press fit etc. A movable nut engaging with the first and second lead screws is formed of a resin or a metal. In other words, the movable nut is formed with a total of two threaded holes engaging with the first and second lead screws. When the two lead screws shown in FIG. 1 are rotated in the same direction at the same rotational speed, the movable nut is longitudinally driven on the lead screws in the right or left direction in the figure according to the direction of rotation of the two lead screws. To the movable nut, an output wire or an output rod material connected with an external load to be driven longitudinally is fixed in an output wire engagement hole provided in the movable nut. Although the case where the two lead screws and threaded holes are provided has been explained as an example, generally, two or more lead screws can be used. In this case, the number of threaded holes is the same as the number of lead screws.
The first and second lead screws configured as described above are rotatably supported by bearings at both ends. In the example shown in FIG. 1, each bearing on one side (right-hand side in FIG. 1) of the first and second lead screws is supported on the frame end part, and the bearing on the other side (left-hand side in FIG. 1) is fixed to the frame end part.
As these bearings, any type of bearing having an ordinary configuration can be used. As the bearing on the left-hand side in FIG. 1, a bearing accommodating a steel ball positioned on the tip end side of the lead screw is typically shown. The steel ball supports a thrust load applied on the tip end side of the lead screw when an external load (not shown) is pulled and driven by the output wire. Alternatively, when the output rod material is used in place of the output wire to drive the external load in the pushing direction, the thrust load must be supported by the bearing provided in the frame end part on the motor side. Thus, either side of the lead screw must bear the load not only in the radial direction but also in the thrust direction according to the application of external load connected to the tip of the output wire or the output rod material.
In the longitudinal motion actuator, when the motor is rotated in a predetermined direction, the first and second gears are rotated in the same direction with respect to each other and in the direction opposite to the direction of rotation of the motor via a pinion fixed to the output shaft of the motor. Thereby, the first and second lead screws are rotated in the same direction with respect to each other, and move the movable nut, which engages with the lead screws, for example, to the motor side in FIG. 1. The output wire connected to the movable nut is pulled, by which the external load is driven. Next, when the motor rotation is reversed, the movable nut moves to the opposite side. The actuator is configured so that the output wire is pulled in the left direction in FIG. 1 at this time by using a spring (not shown) so that the output wire does not deflect.
FIG. 2 is an explanatory view for explaining the relative positional relationship between the pinion and the gear. FIG. 2A shows an example in which two sets of transmission mechanisms each consisting of the gear and the pinion are used, and the transmission mechanisms and the motor output pinion are arranged on a straight line. The two first and second gears are arranged at positions on both sides opposed at an angle of 180° with the pinion being the center. Thereby, the radial loads applied to the transmission mechanisms are cancelled, by which long service life of the bearings etc. can be achieved. However, even if the two gears are not located at the positions opposed at an angle of 180° as shown in FIG. 2B, the radial loads can be cancelled to some degree. FIG. 2C shows an example in which three sets of transmission mechanisms are used. Three first to third gears shown in FIG. 2C are arranged at equal intervals (intervals of 120°) around the pinion. Thereby, the radial loads applied to the gear parts of transmission mechanisms are cancelled, by which long service life of the bearings etc. can be achieved.
In any case of FIGS. 2A to 2C as well, when the pinion fixed to the motor output shaft is rotated in either direction, all of the plurality of gears each having the same configuration, which engage with this pinion, are rotated in the same direction and in the direction opposite to the direction of rotation of the pinion.
FIG. 3A is an explanatory view for explaining power transmission in accordance with the present invention, and FIG. 3B is an explanatory view for explaining power transmission in accordance with a conventional art, being shown for comparison. In the configuration of conventional art shown in FIG. 3B, a first gear is fixed to the motor output shaft, and a second gear engaging with this first gear is provided. Therefore, the construction is made such that at a load applying point at the position where the gears engage with each other, a reaction force to the force applied to the gear is produced, and this reaction force is applied transversely (in the radial direction) to the motor output shaft.
In contrast, the present invention has a configuration such that, as shown in FIG. 3A, the pinion is fixed to the motor output shaft, and the power is transmitted from the pinion to the lead screws via the first and second gears. At this time, the first and second gears and the lead screws are rotated in the same direction. Therefore, the first and second lead screws and gears can use the same parts, so that the equipment can be made common. In addition, by arranging both of the gears symmetrically with respect to the pinion, the reaction forces generated from the gears can be cancelled. In the configuration of the present invention, when the pinion fixed to the motor output shaft is rotated, both of the two gears engaging with the pinion are rotated in the direction opposite to the direction of rotation of the pinion. The load applying point from the pinion to the first and second gears is produced at symmetrical positions on both sides of the pinion, and the directions of the reaction forces are opposite to each other. Thereby, the radial loads on the motor bearing are cancelled into zero, so that the wear resistance of motor bearing can be improved.
Also, the configuration in accordance with the present invention is such that the speed reduction due to the pinion and the gear can be accomplished, and thereby a high output can be obtained. Therefore, this configuration has advantages of smaller size of unit including the motor and saving of electric power. Further, since the characteristics can be changed by changing the reduction gear ratio, the motor part can be standardized easily.
Patent Application
20080015084
