METHOD FOR DESIGNING A ROBOT ARM
The present invention relates to an arm structure for a robot which stands upright and bipedally or otherwise capable of traveling, and in particular to an arm structure having an improved capability to access an object in the front by using a fully extended arm and a method for designing the same.
BACKGROUND OF THE INVENTION
The conventional robots were generally specialized for specific functions, but there is a growing demand for robots which are more similar to humans and are given with a greater versatility. In particular, with the advance in the development of CPUs and programming technology, various upright bipedal or otherwise traveling robots have been proposed. Such robots are capable of serving various practical purposes in homes, work places and fairs. Because such robots are intended to perform jobs which are normally performed by humans, it is necessary and desirable for such a robot to be able to access objects which are required for performing such jobs both quickly and accurately.
In particular, when a robot attempts to reach an object in front of it with a fully extended arm, the fact that the arm undergoes an arcuate motion depending on the angular deviation from a horizontal position of the arm makes the arithmetic computation for controlling the fore-and-aft distance between the free end of the arm or the hand and the object in the front highly complex. If the arm length is increased, the problem associated with the arcuate motion of the arm is reduced, but it detracts from the compact design of the robot. Conversely, if the arm length is reduced excessively, the work efficiency is impaired. It is therefore important to determine the length of the arm in a rational way.
Also, if the arm is controlled by fully taking into account the arcuate motion of the arm, the burden on the CPU increases particularly in an upright walking bipedal robot. In the access control of such an arm, it is desirable to minimize the burden on the CPU.
BRIEF SUMMARY OF THE INVENTION
In view of such problems of the prior art and the recognition by the inventors, a primary object of the present invention is to provide an arm structure for a robot which can favorably carry out jobs which are typically performed by humans.
A second object of the present invention is to provide an arm structure for a robot which can minimize the burden on the CPU when accessing an object in the front with an arm.
A third object of the present invention is to provide a method for designing such an arm structure for a robot.
According to the present invention, such objects can be accomplished by providing a method for designing an arm structure for a robot having an arm which can rotate vertically and forward over a prescribed angle around an axial line extending substantially between two shoulders, comprising the steps of: defining a vertical extent of a region in front of the robot that can be accessed by the arm in a fully extended state; and determining a length of the arm and a height of the axis of rotation of the arm in such a manner that a range of rotational motion of the arm in accessing the region can be covered by a range in which the fore-and-aft distance to the tip of the arm can be linearly approximated.
Thus, even when the trajectory of the arm is approximated by a straight line, the error in the distance to the object can be limited within a prescribed range, and the practicality and economy of computation can be achieved at the same time.
5 In such an arm structure for a robot, by selecting the height of the axis of rotation of the arm to be about 910 mm and allowing the hand to reach 240 mm both below and above this level, it is possible for the robot to reach most of the objects which are intended to be accessed by human
For instance, if the length of the arm is no less than 365 mm and the moveable angle of the arm with respect to a horizontal line is no less than 42 degrees, it is possible for
15 the robot to reach any object in this vertical range while the necessary control algorithm for such a control is simplified because the motion of the free end of the arm or the hand can be safely approximated by a straight line instead of an arcuate curve without giving rise to an error of any more
20 than 25 mm in the fore-and-aft distance.
BRIEF DESCRIPTION OF THE DRAWINGS
Now the present invention is described in the following 25 with reference to the appended drawings, in which:
FIG. 1 is a front view of a humanoid robot embodying the present invention;
FIG. 2 is a left side view of the humanoid robot embody3Q ing the present invention;
FIG. 3 is a top view of the humanoid robot embodying the present invention;
FIG. 4 is a model diagram for explaining the possible motions of the arm;
FIG. 5 is a diagram explaining the geometrical relationship regarding the arm;
FIG. 6 is a graph showing the relationship between D/L and the rotational angle of the arm; and
FIG. 7 is a graph showing the relationship between the tolerated distance error and the necessary arm length as well as the possible range of the swing angle of the arm.
45 DETAILED DESCRIPTION OF THE
FIGS. 1 to 3 show the overall external appearance of a humanoid robot embodying the present invention. This
5Q robot 1 is modeled after a lower grade primary school child, and comprises a head 2 incorporated with a visual unit and a speech unit, a body 3 supporting a control unit and incorporated with batteries, and two legs 5 each having joints so as be able to move substantially in the same way as
55 human legs. The robot is thus adapted to walk on two feet.
The arm 4 of this robot 1 is described in more detail with reference to FIG. 4. This arm 4 comprises a shoulder joint 11 attached to a body 3 so as to be rotatable around a laterally extending axis Al, an upper arm 12 attached to the
60 shoulder joint 11 so as to be rotatable around a fore-and-aft extending axis A2, an elbow joint 13 attached to the upper arm 12 so as to be rotatable around a longitudinal axis A3 of the upper arm 12, a forearm 14 attached to the elbow joint 13 so as to be rotatable around an axis A4 perpendicular to
65 the longitudinal axis A3 of the upper arm 12, and a hand 15 attached to the forearm 14 so as to be rotatable around a longitudinal axis A5 of the forearm 14.