Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
1997-12-15
2001-01-09
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
Reexamination Certificate
active
06170340
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a torque detection mechanism for a flexed meshing type gear drive. In particular, this invention pertains to a torque detection mechanism which is capable of compensating detection errors (rotational ripple) thereof occurring in accordance with rotation of an input shaft even when no torque is transferred. Further, this invention also pertains to a torque detection mechanism which is capable of enhancing linearity of a torque detection output.
2. Related Art Description
A typical flexed meshing type gear drive has a circular rigid internal gear, a circular flexible external gear disposed inside the rigid internal gear, and a wave generator having an elliptical shape fixed into the flexible external gear. The flexible external gear is flexed into elliptical shape by the wave generator, whereby teeth of the external gear which are located on both ends of a major axis of the elliptical shape are meshed with teeth of the rigid internal gear. These meshing portions of the teeth moves circumferentially as the wave generator connected to an input shaft rotates. As a result, relative rotation between the flexible external gear and rigid internal gear occurs in responsive of the difference in number of teeth between the both gears.
As a torque detection mechanism applicable to this type of flexed meshing type gear drive, one has been known that is constituted so that strain gauges as a torque detection element are adhered on an outer circumferential surface of a cup-shaped flexible external gear and, based on detected strain, an amount of torque transferred via the flexed meshing type gear drive is calculated.
Each part of the flexible external gear is repeatedly deformed in its radial direction by the wave generator. Thus, even when no torque is transferred, each part of the flexible external gear is deformed radially as an input shaft connected to the wave generator rotates. More specifically, each part of the elliptically deformed flexible external gear is repeatedly deflected radially at two cycles per rotation of the wave generator connected to the input shaft. As a result, an output corresponding to such deflection is inevitably obtained from the strain gauges.
In order to assure torque detection with high accuracy, it is necessary to delete output error contents (rotational ripple) due to such cyclic deflection from a detected output so as to obtain an amount of strain corresponding only to the transferred torque. The strain varies in the form of a sign wave having a phase of 180°, and therefore it can be deleted by a combination of outputs from a pair of torque detection elements such as strain gauges which are provided on the flexible external gear at an angular interval of 90°.
Conventionally, a pair of strain gauges are adhered on an outer circumferential surface of the flexible external gear so that these strain gauges are arranged at an angular interval of 90° around a rotational axis of the gear drive, and a combined or synthesized output of these strain gauges is used to calculate a torque transferred through the gear drive.
It is necessary for enhancing a detection accuracy of torque transferred through the flexed meshing type gear drive to improve linearity of torque detection output as well as to make sure of deleting rotational ripple included in the torque detection output.
SUMMARY
Accordingly, an object of this invention is to greatly improve detection accuracy of transferred torque compared to the case where a conventional torque detection device is employed in which torque detection elements are arranged at an angle of 90°.
Namely, an object of this invention is to propose a torque detection mechanism for a flexed meshing type gear drive which is capable of carrying out a high accurate torque detection by means of deleting rotational ripple included in an torque detection output.
In addition, an object of this invention is to propose a torque detection mechanism for a flexed meshing type gear drive which is capable of carrying out a high accurate torque detection by improving linearity of a torque detection output.
Furthermore, an object of this invention is to propose a torque detection mechanism for a flexed meshing type gear drive which is able to delete rotational ripple included in a torque detection output more certainly than in a conventional torque detection mechanism and at the same time to greatly improve linearity of the torque detection output.
In order to achieve the above objects, a torque detection mechanism for a flexed meshing type gear drive is constituted so that it comprises a first torque detection means which has a pair of torque detection elements arranged on at least one of outer and inner surfaces of a flexible external gear except for where external teeth are formed, these torque detection elements being arranged at an angular interval of 90° around a center axis of the flexible external gear, and a second torque detection means which has a pair of torque detection elements arranged at an angular interval of 90° around the center axis of the flexible external gear. The second torque detection means is arranged at an angular position (k×45°) offset from the first torque detection means around the center axis (k is odd number). Further, detection outputs of these first and second torque detection means are synthesized, based on which a torque transferred via the flexed meshing type gear drive is detected.
According to the torque detection mechanism of this invention, rotational ripple amplitude included in the torque detection output can be greatly reduced and a high accurate detection of transferred torque can be realized. At the same time, it is possible to improve linearity of torque detection output, whereby a detection accuracy of transferred torque can also be enhanced.
In order to further improve linearity of torque detection output, it is preferable that the second torque detection means is arranged at an angular position between 90 to 270° angles offset from the first torque detection means around the center axis.
In addition, for the purpose of further improvement of linearity of torque detection output, it is preferable to provide, in addition to the first and second torque detection means, a third torque detection means having a pair of torque detection elements arranged on at least one of outer and inner surfaces of a flexible external gear except for where external teeth are formed, these torque detection elements being arranged at an angular interval of 90° around a center axis of the flexible external gear, and a fourth torque detection means which has a pair of torque detection elements arranged at an angular interval of 90° around the center axis of the flexible external gear. In this case, the second torque detection means is arranged at an angular position 45° offset from the first torque detection means around the center axis, while the third and fourth torque detection means are arranged respectively at angular positions 180° and 225° offset from the first torque detection means around the center axis.
Whereas, it is also possible to adopt such an arrangement of the first to fourth torque detection means that the second, third and fourth torque detection means are placed at angular positions offset from the first torque detection means around the center axis by 22.5, 45 and 67.5°, respectively. With this arrangement, the rotational ripple amplitude included in the torque detection output can be reduced further more.
Instead of the above arrangement, the first to fourth torque detection means may be placed as follows for deleting the rotational ripple from the torque detection output. Namely, the positional relationship between the first and second torque detection means is the same as that in the above-mentioned arrangement. While, the third and fourth torque detection means are placed at angular positions offset from the first and second torque detection means around the center axis by 90°, respectively.
One of a flexed meshing typ
Godler Ivan
Hashimoto Minoru
Horiuchi Masashi
Burns Doane Swecker & Mathis L.L.P.
Fuller Benjamin R.
Harmonic Drive Systems Inc.
Thompson Jewel V.
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