Machine element or mechanism – Gearing – Directly cooperating gears
Patent
1996-11-07
1998-07-21
Marmor, Charles A.
Machine element or mechanism
Gearing
Directly cooperating gears
74417, 74421A, F16H 3704, F16H 5702
Patent
active
057821330
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a driving unit, preferably intended for an industrial robot, comprising an electric motor having a shaft which, via a reduction angle gear unit, is connected to an output shaft. The driving unit comprises a motor and a reduction gear for driving the arm movements of the robot.
BACKGROUND ART
An industrial robot of a so-called anthropomorphic type has a stand which is rotatably arranged on a foot and which supports a first robot arm which is rotatable in relation to the stand. At the outer end of this arm, a second robot arm is rotatably journalled. This second arm supports, at its outer end, a robot hand which is provided with a tool attachment and which is rotatable in two degrees of freedom relative to the second arm. For each one of the above-mentioned robot arms and the robot hand, a driving unit is provided. The driving units for the first and second robot arms each comprise a motor and a reduction gear with very high gear ratio, for example a so-called RV gear (rotary vector) or a so-called harmonic drive. These driving units are often placed in the stand on opposite sides of the center of rotation of the first arm and are oriented with their respective motor shafts in parallel with the rotary axis of the first arm (see e.g. U.S. Pat. No. 4,396,344, FIG. 5). A drawback which arises when the driving units extend from the stand is that the "elbow-room" of the robot, defining the radius within which no objects may exist, increases and hence reduces the operating range of the robot. One way of solving the problem is to use motors with a short rotor with a large diameter. However, these are expensive.
Driving motors for industrial robots currently consist of inverter-fed synchronous motors with permanent magnets in the rotor. The performance of these motors is primarily determined by the volume and the ratio between the length of the rotor and its diameter. A large diameter provides a greater torque whereas a smaller diameter provides a smaller moment of inertia and hence a higher acceleration. The most cost-effective motor is obtained when the quotient between the length of the rotor and its diameter approaches 1, which, because of the extension of the stator winding and bearing shields, gives the motor a long and narrow appearance. The inferior torque which is obtained with such a motor may be compensated for by a higher speed and a greater gear ratio.
The number of revolutions of the motor is largely determined by the speed of the electronics in the inverter which is to drive the motor, and currently speeds up to about 4,000 RPM (revolutions per minute) are possible. To be able to utilize a motor with a speed of up to 4,000 RPM, the gear must be capable of reducing the speed by a factor of 240. With acceptable gear wheel diameters, this cannot be achieved with a parallel-axes gear unit in two steps. This necessitates changing to a three-step gear unit.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a cost-effective driving unit for an industrial robot, which driving unit comprises a motor and a gear unit and which possesses the properties of high reduction gear ratio with a minimum of play, fast acceleration and a minimum overall volume. This is achieved according to the invention by a driving unit comprising a transversely oriented, elongated motor, the projection of which lies on the gear case, and a gear unit with two steps. The first step comprises a bevel gear pair and the second step a cylindrical gear pair.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained in greater detail by describing embodiments with reference to the accompanying drawing, wherein
FIG. 1 is a side view of a driving unit according to the invention, and
FIG. 2 is a vertical section taken through the driving unit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The driving unit shown in the drawing is intended to be fixed to the stand of an industrial robot of the type described above for rotating, for example, the first robot arm
REFERENCES:
patent: 1894927 (1933-01-01), Schmitter
patent: 2221292 (1940-11-01), Trout et al.
patent: 4270783 (1981-06-01), Sorensen et al.
patent: 4396344 (1983-08-01), Sugimoto et al.
patent: 5375479 (1994-12-01), Kouno et al.
patent: 5558174 (1996-09-01), Avitan et al.
Transactions of the ASME, Journal of Mechanical Design, vol. 112, pp. 430-436, dated Sep. 1990.
Asea Brown Boveri AB
Grabow Troy
Marmor Charles A.
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