ARM STRUCTURE OF AN INDUSTRIAL ROBOT

Abstract: Industrial robot has an elevating shaft (14), a 1st arm (16) mounted at the upper end of the elevating shaft. A 2nd arm (20) which is pivotally attached to the forward end of the 1st arm via a transmission/reduction gear box (18) fixed to the 1st arm's forward end. A number of coupling bolts (22) extend the length of the interior of the 1st arm. Each bolt has one end (22b) fixed to a gear box flange (18a) and its other end (22a) projecting beyond the rear end of the 1st arm. Tightening nuts (24) are fitted at one or both ends of the bolts and serve to connect the 1st arm gear box while imposing preliminary compressive force on the 1st arm.

Description: The present invention relates generally to an arm structure for the movable unit of an industrial robot and, more particularly, to an industrial robot comprising an effective and inexpensive mechanism for improving the load capacity of the arm structure thereof in conveying a weight such as a workpiece held by a robot hand attached to the extremity of the arm structure or in executing robot work in a loaded state with a tool held by the robot hand. In a horizontal multi-articulate type robot applied to precision assembling work, in particular, among the recent industrial robots used for industrial purposes, movable robot units, such as a vertical shaft capable of vertically movement relative to a robot base unit, a horizontal robot upper arm and a horizontal robot forearm, are formed in hollow component structures, and drive sources for driving the shaft, the horizontal arms and a robot wrist attached to the extremity of the horizontal arm, transmission mechanisms, reduction gear mechanisms, wiring and piping are housed within the hollow component structures to prevent the horizontal articulated robot from generating dust and oil during operation. However, when handling a weight such as a workpiece with a robot hand or a tool attached to the extremity of a wrist, a tensile load and a bending load act inevitably on the robot arms, and the influence of the tensile and bending loads on the robot arms formed in hollow structures is more significant than on robot arms formed in rigid structures. This influence on the robot arms cannot be entirely disregarded when the horizontal articulated robot is applied to precision assembling work. Accordingly, an object of the present invention is to provide an arm structure for an industrial robot, capable of mitigating the influence of a load acting as the above-mentioned tensile load and bending load. Another object of the present invention is to provide a horizontal multi-articulate type industrial robot having a light weight and able to resist the tensile and bending loads. JP-U-59 176785 discloses an industrial robot comprising a vertical robot shaft; a first robot arm secured to an upper end of the vertical robot shaft; transmission-reduction gear means contained in a case and secured to a free end of the first robot arm by bolts and nuts respectively engaging at least one ends of each of the bolts; and a second robot arm pivotally joined through the transmission-reduction gear means to the free end of the first robot arm, and in accordance with the present invention, such a robot is characterised in that the bolts each extend through the interior of the first robot arm, with one end fastened to the case containing the transmission-reduction gear means and the other end projecting from and fastened to a rear end of the first robot arm so that the bolts preload the first robot arm with a compressive force. The above and other objects and advantages of the present invention will be described in detail hereinafter with reference to a preferred embodiment thereof illustrated in the accompanying drawings, in which: Figure 1 is a fragmentary perspective view of a horizontal multi-articulate type industrial robot incorporating an arc structure, in a preferred embodiment according to the present invention; and, Figure 2 is a sectional view taken along the line II-II in Fig. 1. Referring to Figs. 1 and 2 showing the essential portion of a horizontal articulated industrial robot incorporating an arm structure according to the present invention, the industrial robot 10 has a swiveling body 12. The swiveling body 12 is a component capable of swiveling about a vertical axis relative to a bed, not shown, in directions indicated by double-headed arrow ϑ. A vertical shaft 14 is mounted for vertical movement in directions indicated by a double-headed arrow Z on the swiveling body 12. A first arm 16 included in a horizontal robot arm structure is attached to the top of the vertical shaft 14 so as to extend horizontally to the front. A transmission-reduction gear box 18 comprising a transmission-reduction gear and a case containing the transmission-reduction gear is attached to the free end of the first arm 16. A second arm 20 included in the horizontal arm structure is attached to the lower part of the transmission-reduction gear box 18 for a turning motion in a horizontal plane about a vertical axis in directions indicated by a double-headed arrow U so as to extend horizontally similarly to the first arm 16. Although not shown in the drawings, ordinarily a robot wrist is provided on the free end of the second arm 20 for handling various loads through robot actions. A motor, not shown, for the turning motion of the second arm 20 is housed in the first arm 16. The output of the motor is transmitted through the transmission-reduction gear, not shown, contained in the transmission-reduction gear box 18 and including, for example, a skew gear mechanism for the second arm 20, to drive the second arm 20 for a turning motion within a horizontal plane. According to the present invention, the transmission-reduction gear box 18 is joined to the free end of the first arm 16 with a plurality of elongated coupling bolts 22, and each coupling bolt 22 has one end 22a projecting from the rear end of the first arm 16 and fastened to the rear end of the first arm 16 with a fastening nut 24, and the other end projecting to the front from an appropriate flange 18a formed in the end surface of the transmission-reduction gear box 18 and fixed to the front face of the flange 18a with a fastening nut 26. That is, the elongated coupling bolts 22 are extended through the interior of the first arm 16 and the respective opposite ends of the elongated coupling bolts 22 are fastened to the opposite ends of the first arm 16 to preload the first arm 16 by applying a compressive force beforehand to the first arm 16. Accordingly, when the robot 10 holds a load by means of the robot wrist provided on the free end of the second arm 20 for robot actions, and thereby the long first arm 16 is subjected to a tensile force and a bending moment caused by the load, the compressive force applied beforehand to the first arm 16 suppresses the influence of the tensile force and the bending moment on the first arm 16. When a component similar to the transmission-reduction gear box 18 is provided on the extremity of the second arm 20, the second arm 20 may be provided with the same construction for preloading the second arm 20 by applying a compressive force to the second arm 20 as that for applying beforehand the compressive force to the first arm 16, to effect both coupling such a component to the second arm 20 and preloading the second arm 20 by a compressive force. Although the coupling bolts 22 provided on the first arm 16, in the embodiment described hereinbefore, are fastened at the respective opposite ends thereof to the first arm 16 with the fastening nuts 24 and 26, respectively, each coupling bolt 22 may be provided with a bolt head at one of the opposite ends 22a and 22b thereof and may be fastened to the first arm 16 at the other end with the fastening nut 24 or 26. Furthermore, when the first arm 16 has a rectangular cross section, it is preferable to extend the coupling bolts 22 respectively along the four internal corners and contiguously with the internal wall surfaces of the first arm 16 as shown in Fig. 2 to secure sufficient internal space 27 for wiring and piping to enable the application of a sufficient longitudinal compressive force to the first arm 16. Still further, when the first arm 16 has a circular cross section, it is desirable to arrange the plurality of coupling bolts 22 along the internal circumference of the first arm 16 at regular angular intervals. As apparent from the foregoing description, the arm structure of an industrial robot according to the present invention employs elongated coupling bolts for attaching a transmission-reduction gear box to one end of an arm, and the coupling bolts are extended through the interior of the arm and are fastened to the arm so as to preload the arm by a compressive force. Therefore, the influence of a tensile force and bending moment caused by a load on the arm can be satisfactorily reduced. Naturally, the present invention is also applicable to the respective arms of other articulated type industrial robots, not to mention the horizontal multi-articulated type industrial robot as specifically described herein with reference to the preferred embodiment thereof.

Claims: 1. An industrial robot comprising a vertical robot shaft (14); a first robot arm (16) secured to an upper end of the vertical robot shaft; transmission-reduction gear means contained in a case (18) and secured to a free end of the first robot arm by bolts (22) and nuts (24) respectively engaging at least one ends of each of the bolts; and a second robot arm (20) pivotally joined through the transmission-reduction gear means to the free end of the first robot arm; characterised in that the bolts (22) each extend through the interior of the first robot arm (16), with one end fastened to the case (18) containing the transmission-reduction gear means and the other end projecting from and fastened to a rear end of the first robot arm (16) so that the bolts preload the first robot arm with a compressive force. 2. A robot according to claim 1, wherein the nuts (24) are fastened to the bolts at the rear end of the first robot arm. 3. A robot according to claim 1 or claim 2, wherein the first robot arm (16) is formed as a hollow structure having a rectangular cross section. 4. A robot according to claim 3, wherein there are four of the bolts (22) extending through the first robot arm (16) respectively along four corners of the first robot arm. 5. A robot according to claim 1 or 2, wherein the first robot arm (16) is formed as a hollow structure having a circular cross section, and the bolts (22) are equiangularly arranged along the circumference of the first robot arm. 6. A robot according to any one of the preceding claims, wherein the first and second arms (16,20) are horizontal articulated arms disposed in a horizontal position relative to the vertical axis.

Inventors: NIHEI, RYO, TERADA, AKIHIRO, TORII, NOBUTOSHI
Applicants: FANUC LTD.
Application year: 1987
Main classification: B25J9
IPC codes: B25J9, B25J18