Abstract:
In a robot machine, a hand is rotatably mounted on one end of an arm. The hand is provided with two sets of grasping units each including a pair of opposed fingers which are used to grasp or release an article, for example, a workpiece to be machined by a machine tool. A piston-cylinder assembly is provided for rotating the hand through a ninety degree angle.

Description:
This is a continuation of application Ser. No. 292,303 filed Aug. 12, 1981, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to robot machines and in particular to robot hands of a robot machine. 
     A robot hand has been proposed in which two sets of workpiece grasping units are provided for the fore end of an arm for the purpose of decreasing the number of opeations of the hands for loading or unloading the workpiece on or from a machine tool capable of machining continuously with the robot hand. More particularly, while one grasping unit of the robot hand utilized to unload a workpiece secured to the machine tool by a chuck, for example, is made to be idle, the other grasping unit is actuated to grasp another workpiece to be subsequently loaded. As the robot hand approaches a chuck, the idle grasping unit is aligned with the workpiece and, then, the fingers of that grasping unit are operated to grasp the workpiece. When the chuck releases the workpiece, the other grasping unit is coaxial with the chuck and, then, the jaws of the chuck are closed to securely load the new workpiece on the machine tool. Then, the workpiece removed from the machine tool is grasped by the idle grasping unit. The hand, which has finished supplying the new workpiece, is returned to a predetermined position. Thus, when compared with a robot machine having only one hand, it is possible to save one conveyance operation corresponding to one reciprocating motion, during each operation described above. 
     However, during the above-described operations, when the center of the chuck is shifted from alignment with the center of one grasping unit to alignment with the center of the other grasping unit, the realignment has occurred through motion of the arm. In such a case, depending on the relative position of the grasping units, it is necessary to move the hand in the vertical direction or to reverse the motion of the entire hand. 
     In this case, since the weight of the arm acts as a load on a member to be manipulated some operating power is lost and quick operation is impaired. Moreover, vibrations are liable to be induced, making it difficult to accurately align centers. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved robot machine capable of eliminating the disadvantages described above. 
     Another object of the present invention is to provide a robot machine capable of reducing by one half, the number of operations required for accurately positioning the robot hand. 
     According to the present invention, there is provided a robot machine having a hand rotatably mounted on one end of an arm and two sets of grasping units equally spaced from a center of rotation of the hand. Each grasping unit includes a pair of opposed fingers and means for causing the fingers to move towards and away from a grasping center for grasping or releasing an article. Means are provided for rotating the hand through an angle subtended by the grasping centers of the pair of opposed fingers relatives to the center of rotation of the hand. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a side view showing an arm of a robot machine and a pair of grasping units according to the present invention; 
     FIG. 2 is a side view showing the entire robot machine; and 
     FIGS. 3A through 3D are partial side views showing the manner of grasping and releasing workpieces using the grasping units of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The robot machine shown in FIG. 1 including an arm 1 which is movable according to an instruction and a hand 2 mounted on the free end of the arm to be rotatable about a axis of rotation or pivot axis 0. The hand 2 is provided with a first grasping unit 10 having fingers 11 and 12 and a second grasping unit 20 having fingers 21 and 22. As shown by dotted lines, each grasping unit 10 and 20 is driven by a drive source, for example, air cylinders 13 and 23, respectively, through a suitable link mechanism 9 to swing towards and away from respective grasping center points a and b which are equally spaced from the axis of rotation 0 and symmetrical with respect to a reference line Y, which is the longitudinal axis of the arm 1. 
     The hand 2 and the grasping units 10 and 20 shown in FIG. 1 constitute a portion of the robot machine 8, as shown in FIG. 2. Thus, the arm 1 is mounted on a base 4 through supports 3. A piston cylinder assembly 5 having a piston rod 6 is provided. The cylinder is connected to the rear end of the arm 1 to be swingable about a pivot point P. The front end of the piston rod 6 is connected to the fore end of the arm 1 through a link 7 so as to permit selective rotation of the hand 2. The reciprocating motion of the piston rod 6 rotates the robot hand 6 about the pivot axis 0 by an angle Θ (FIG. 1) subtended by the grasping center points a and b so as to position the grasping center of the second grasping unit 20 at point a or to position the grasping center of the first grasping unit 10 at point b. 
     Referring now to FIGS. 3A and 3B, the operation for loading a workpiece on a horizontal type machine tool, for example, a lathe (not shown) will be described. In FIG. 3A, W represents a workpiece already loaded on the lathe and X represents another workpiece to be substituted for the workpiece W. FIG. 3A shows a condition in which the hand 2 is advanced to bring the grasping center b of the second grasping unit 20 into axial alignment with a rotary axis C of the chuck (not shown) of the lathe. FIG. 3B shows a condition in which the fingers 21 and 22 of the second grasping unit 20 have just grasped the workpiece W. At this time, the jaws (not shown) of the chuch may release the workpiece W. 
     The hand 2 is constructed, in any appropriate manner, such that when its movement is obstructed by the jaws of the chuck, it is moved slightly in a direction perpendicular to the sheet of drawing. FIG. 3C shows a condition in which the hand 2 has been rotated 90° from the position shown in FIGS. 3A and 3B by the motion of the piston rod 6. At this time, the workpiece W grapsed by the second grasping unit 20 has been released from the chuck, whereas the new workpiece X grasped by the first grasping unit 10 is brought into axial alignment with the center of the chuck. When the hand 2 is restored to its original axial position, the fingers of the chuck are closed to secure the workpiece X to the lathe. 
     FIG. 3D shows a condition in which the fingers of the first grasping unit 10 are opened and the hand 2 has risen to release the workpiece. 
     During a series of operations such as that described above, the accurate positioning of the the first and second grasping units 10 and 20, respectively, by means of the arm 1 is required only when the second grasping unit 20 must be accurately positioned relative to the workpiece W, as shown in FIG. 3B. The succeeding positioning of the first grasping unit can be accomplished by merely rotating the hand 2 since the first grasping unit 10 moves into the previous position of the second grasping unit 20 without any need for operating the arm 1. 
     As described above, according to the present invention, the number of positionings of the robot hand which must be accurate is decreased to one half of the number required by prior art robot hands. Therefore, it is possible to eliminate all such difficulties as loss of power, sluggish movement and vibration which are caused by the weight of the hand. Moreover, the rotary movement of the hand 2 is restricted to a space in which the hand 2 is moved by the arm 1 so that no additional space is required, which is advantageous for machine tools or the like. 
     The above description is by way of example and not by way of limitation. Various modifications will be apparent to those skilled in the art upon reviewing the present application and are intended to be included within the scope of the appended claims.