1. Field of the Invention
The present invention relates to an orthogonal two-axis moving apparatus capable of moving in two orthogonal directions and, more particularly, to an orthogonal two-axis moving apparatus suitable for an industrial robot structure moving (rotating) at high speed.
2. Related Background Art
An orthogonal two-axis moving apparatus in which belts are looped around a plurality of pulleys in a crossed shape is proposed by the present applicant in Japanese Patent Application No. 01-188913.
In this orthogonal two-axis moving apparatus, for example, as shown in FIG. 22, a pair of orthogonal guide members b.sub.1 and b.sub.2 and a pair of orthogonal guide members c.sub.1 and c.sub.2 are mounted to extend through a central slide block a. Slide members d.sub.1, d.sub.2 and e.sub.1, e.sub.2 reciprocal in two orthogonal directions are respectively mounted in the pairs of orthogonal guide members b.sub.1 and b.sub.2 and c.sub.1 and c.sub.2. Blocks f and g are respectively fixed on two ends of the pair of slide members d.sub.1 and d.sub.2, and blocks h and i are respectively fixed on two ends of the pair of slide members e.sub.1 and e.sub.2.
Rotatable pulleys j, k, and l are mounted on the three blocks f to h of the four blocks f to i, respectively. Four rotatable pulleys m, n, p, and g are mounted on the slide block a. A belt r, two ends of which are locked by the block i, is looped around the pulleys m to g. The pulleys j and k are driven by driving motors s and t, respectively. Upon driving of the motors s and t, the slide block a is linearly moved along the slide members d.sub.1 and d.sub.2, and the slide members e.sub.1 and e.sub.2 are linearly moved in a direction perpendicular to the extension direction of the slide members d.sub.1 and d.sub.2.
When this orthogonal two-axis moving apparatus is applied to an industrial robot, the slide members d.sub.1 and d.sub.2 stand upright, and an end effector u (shown in FIG. 23) such as a hand is attached to the distal end of the block i, thereby constituting a robot arm with two (2) degrees of freedom. In addition, if this industrial robot is to be used as a robot arm with three (3) degrees of freedom, the block g of this orthogonal two-axis moving apparatus is mounted on a rotary driving part v, as shown in FIG. 23. That is, the robot with 3 degrees of freedom generally comprises a cylindrical robot.
When the above orthogonal two-axis moving apparatus is, however, used as a cylindrical robot, in the state shown in FIG. 23, the mass of the end effector u acts on the guide members b.sub.1 and b.sub.2 and the slide members d.sub.1 and d.sub.2 serving as the vertical slide mechanism to cause torsion as a whole upon rotation of the whole of the moving apparatus by the rotary driving portion v.
In order to prevent this torsion, it is necessary that the diameter of each of the slide members d.sub.1 and d.sub.2 is increased or the number of slide members d.sub.1 and d.sub.2 is increased. These modifications, however, result in an increase in size of the apparatus.
When the end effector u is vertically moved, the slide members e.sub.1 and e.sub.2 and the blocks h and i are vertically moved as a whole together with the slide block a. Therefore, other members cannot be located below the blocks h and i, and a large dead space is undesirably formed to decrease the efficiency of space utilization. In addition, since the vertically moving mass is large, a driving motor torque is increased when a cylindrical arrangement is employed to move a large mass in a direction along the lines of the force of gravity. A belt as a power transmission mechanism must then have a larger thickness.