JOINT MECHANISM OF INDUSTRIAL ROBOT

Abstract: In a joint mechanism of an industrial robot having a second arm (1) or stationary base rotatably supporting via a bearing (8) a joint shaft (11) integrally attached to a first arm in alignment with the center line of rotation of the first arm (2), the joint shaft (11) is made in the form of a crank and its one half is made in the form of a cylinder, and a cable (3) is passed through inside the cylinder portion of the joint shaft (11). A motor (5) is attached to the second arm (1) or stationary base with its output shaft (13) positioned in alignment with the center line of rotation of the first arm (2), and the motor output shaft (13) is connected directly or via a harmonic drive (6) to the joint shaft (11), whereby sliding portions in a motive power transmission section are reduced, thereby lessening the generation of dust.

Description: This invention relates to a joint or articulation mechanism of industrial robots according to the preamble of claim 1. Such a joint mechanism is known from US-A-4 547 120. However, in this mechanism, the drive shaft of the motor provided in the form of a cylinder/piston assembly is connected to the motor shaft connection portion in the region of the empty room to which the cable passes so that a simple arrangement of the driving mechanism is complicated and the generation of dust is not entirely avoidable. Fig. 1 shows the structure of a robot joint which had been known to our company prior to the completion of the present invention. In this drawing, the distal end of an upper arm ( a second arm ) (1) supports a joint shaft (11) by means of a motor (5), a harmonic drive (6) and a bearing (8). This joint shaft (11), in turn, supports a forearm ( a first arm ) (2) secured thereto. (3) designates a cable which supplies motive power, electric power used for various detection purposes, air, etc. to motors and/or hands ( not shown ) provided at the distal end of the forearm (2). (4) designates protective bushes for the cable (3), (7) a key formed on the drive shaft (13) of the motor (5), (9) a stopper plate, and (10) a spacer. Incidentally, the arrangement wherein the harmonic drive (6) is attached to the joint shaft of the robot is disclosed in US Patent No. 4,096,766, hence, no further description will be given here. The operation of the foregoing mechanism will now be described. As the motor (5) rotates, the output end ( the lower end ) of the harmonic drive (6) rotates at a reduced speed, so that the joint shaft (11) directly connected to the output end and the forearm (2) begin to swivel. Since the robot joint mechanism shown in Fig. 1 has the foregoing structure, the motive power transmission elements must be provided on the joint shaft (11), and the cable (3) for supplying power, air, etc. beyond the joint must be led out of the arms in the joint section. On the other hand, an industrial robot of the type wherein a cable (3) is stored inside a joint section is also known as disclosed in Japanese Patent Application Laid-Open No. 62-48485. The joint mechanism of this industrial robot publicly known is improved so that the cable is stored inside the joint section, but is defective in that a joint driving motor is located apart from the joint axial line, and a motive power transmission mechanism including transmission gears, belts, etc. must be provided between the motor drive shaft and the joint drive section, in addition to a reduction gearing which is primarily necessary for joint driving (but, sometimes unnecessary depending on the type of motor used ). Therefore, this type is complicated in the structure of the motive power transmission mechanism, requires the adjustment of engagement between transmission gears, tension of belts, etc., and is not adapted for clear ( little-dust-generation ) robotization because the transmission gears, belts, etc. include a lot of sliding portions or dust generating portions. It is an object of the present invention to provide a clean ( little-dust-generation ) joint mechanism of industrial robots whose cable for supplying power, air, etc. beyond a joint section is not necessary to be led out of arms in the joint section. This object is solved in accordance with the present invention by a joint mechanism of an industrial robot which, according to claim 1, has a second arm or stationary base rotatably supporting via a bearing 8 a joint shaft 11 integrally attached to a first arm 2 in alignment with the center line of rotation 11F of said first arm 2, comprising: a motor 5 attached to said second arm 1 or stationary base and having a drive shaft 13, wherein said joint shaft 11 is made up of a motor shaft connection portion 11C mechanically connected directly or via an attaching member to said motor drive shaft 13 in alignment with the center line of rotation 11F of said first arm 2, a joint shaft portion 11A attached integrally to said first arm 2 and formed with an empty room 11G therein through which at least a cable 3 can pass, and a coupling portion 11E connecting said motor shaft connection portion 11C with said joint shaft portion 11A such that the opening of said empty room 11G suffers substantially no restriction, wherein the drive shaft 13 of said motor 5 is in alignment with the center line of rotation 11F of said first arm 2, said motor drive shaft 13 and said motor shaft connection portion 11C of said joint shaft 11 are connected directly or via an attaching member together in alignment with the aforementioned center line of rotation 11F, said attaching member for connecting together said motor drive shaft 13 and said motor shaft connection portion 11C of said joint shaft 11 is a harmonic drive 6, and the inner surface of said empty room 11G formed in said joint shaft portion 11A of said joint shaft 11 is provided with a protective bush 4 for cable protection. Another feature of the present invention is that the joint shaft forming part of the joint mechanism is made up of the motor shaft connection portion, a joint portion including the empty room, and a crank-shaped coupling portion, whereby the cable is passed through the empty room. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing the structure of a robot joint known to our company; Fig. 2 is a sectional view showing the structure of a joint according to an embodiment of the present invention; and Fig. 3 is a perspective view of the joint shaft shown in Fig. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will now be described with reference to the drawings. Fig. 2 shows the structure of a robot joint of the present invention, in which reference numerals pointing at respective elements correspond to those shown in Fig. 1. (12) designates a nut for securing the first arm or forearm (2) to the joint shaft (11). The significant different point of the present invention from the structure shown in Fig. 1 is the configuration of the joint shaft (11), that is, it has a crank shape and its one half is made in the form of a cylinder. In Figs. 2 and 3, (11A) designates a cylinder portion serving as a joint shaft portion which is secured to the first arm or forearm (2) by means of the nut (12) and rotatably connected via the bearing (8) to the second arm or upper arm (1) serving as a stationary base, and which has an empty room (11G) formed in the inside thereof. (11B) designates a threaded portion on which the nut (12) is fitted, and (11C)(11C) designate tapped holes for bolts and a shaft portion, respectively, these being used for connection with the harmonic drive (6), thus serving as a motor shaft attaching portion. The shaft portion (11C) is formed so that its center axial line (11F) is in line with that (11F) of the cylinder portion (11A). (11E) designates a crank-shaped coupling portion for connecting the cylinder portion (11A) with the shaft portion (11D). As shown clearly in Fig. 2, the joint shaft (11) of the foregoing configuration is assembled in such a manner that in the inside of the upper arm (1) the shaft portion (11D) is connected by means of bolts ( not shown ) fitable in the tapped holes (11C) to the harmonic drive (6) connected to the motor (5), an upper portion of the cylinder portion (11A) is rotatably connected via the bearing (8) to the upper arm (1), and a lower portion of the cylinder portion (11A) is tightened and secured to the forearm (2) by means of the nut (12) fitable on the threaded portion (11B) of the cylinder portion (11A). The protective bush (4) is inserted in the cylinder portion (11A), and the cable (3) is passed through the bush (4) for supplying motive power, electric power used for various detection purposes, air, etc. to motor and/or hands provided at the distal end of the forearm (2); therefore, the cable (3) is incorporated in the joint section without being exposed outside the upper arm (1) and the forearm (2). In the foregoing arrangement, since the coupling portion (11E) of the joint shaft (11) is offset in the elongating direction of the forearm (2) and disposed on the left-hand side in Fig. 2, thereby providing a relief space for the cable (3) by virtue of the crank portion, the cable (3) can never be damaged even when the forearm (2) swivels. Because of the foregoing structure the cable (3) is not exposed outside, so that the external beauty of the robot is further enhanced and less danger of damage is imposed on the cable (3). Although in the embodiment the motor (5) is connected via the harmonic drive (6) to the joint shaft, the joint shaft may be directly connected to the output shaft (13) of the motor (5). Although the bearing (8) is shown as being of one row type, using two or more row type will be understood to be better from the viewpoint of strength. Further, although in the embodiment the joint shaft (11) according to the present invention is described as being used in the joint section between the upper arm (1) and the forearm (2), the intended object of the present invention can of course be attained even when the present joint shaft (11) is employed in the joint section between a stationary base and an arm. As described above with reference to the embodiment, the present invention makes the joint shaft in the form of a crank and its one half in the form of a cylinder as shown in Fig. 3; consequently, the cable can be wired through a central portion of the cylinder portion of the joint shaft ( without being led out of the arms ), so that the external beauty of the robot is further enhanced and the possibility of the cable being damaged becomes very little. Further, the output shaft of the motor is positioned in alignment with the center line of rotation of the first arm, the motor is mounted on the second arm or stationary base, and the output shaft of the motor is connected directly or via an attaching member such as the harmonic drive to the joint shaft; consequently, sliding portion in the motive power transmission section are remarkably reduced, thereby lessening the generation of dust, whereby there can be provided the clean joint mechanism of industrial robots.

Claims: A joint mechanism of an industrial robot having a second arm (1) or stationary base rotatably supporting via a bearing (8) a joint shaft (11) integrally attached to a first arm (2) in alignment with the center line of rotation (11F) of said first arm (2), comprising: a motor (5) attached to said second arm (1) or stationary base and having a drive shaft (13), wherein said joint shaft (11) is made up of a motor shaft connection portion (11C) mechanically connected directly or via an attaching member to said motor drive shaft (13) in alignment with the center line of rotation (11F) of said first arm (2), a joint shaft portion (11A) attached integrally to said first arm (2) and formed with an empty room (11G) therein through which at least a cable (3) can pass, and a coupling portion (11E) connecting said motor shaft connection portion (11C) with said joint shaft portion (11A) such that the opening of said empty room (11G) suffers substantially no restriction, characterized in that the drive shaft (13) of said motor (5) is in alignment with the center line of rotation (11F) of said first arm (2), said motor drive shaft (13) and said motor shaft connection portion (11C) of said joint shaft (11) are connected directly or via an attaching member together in alignment with the aforementioned center line of rotation (11F), said attaching member for connecting together said motor drive shaft (13) and said motor shaft connection portion (11C) of said joint shaft (11) is a harmonic drive (6), and the inner surface of said empty room (11G) formed in said joint shaft portion (11A) of said joint shaft (11) is provided with a protective bush (4) for cable protection. A joint mechanism of an industrial robot according to claim 1, wherein said coupling portion (11E) of said joint shaft (11) is in the form of a crank. A joint mechanism of an industrial robot according to claim 1, wherein said coupling portion (11E) of said joint shaft (11) is offset in the elongating direction of said first arm (2).

Inventors: IWATA, MASANARI@MITSUBISHI DENKI K.K., Iwata, MasanariµMitsubishi Denki K.K.
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1988
Main classification: B25J19
IPC codes: B25J17, B25J9, B25J19