1. Field of the Invention
The present invention relates to a measuring system for measuring the position of a tool center point (TCP) with respect to the tool mounting surface of a tool mounted at the forward end of an arm of a robot or, in particular, to a measuring system for measuring the position of the tool center point with respect to the tool mounting surface by combining the robot with a light receiving device such as a camera or a PSD (position sensing detector).
2. Description of the Related Art
A method to measure the position of the tool center point with respect to the tool mounting surface of a robot using the three-point touch-up or the six-point touch-up capability is known. FIG. 1 shows a typical arrangement used for application of this method. As shown in FIG. 1, the robot 1 is connected to a robot control unit 5 for controlling the robot 1, and a tool 30 is mounted at the forward end of the arm of the robot 1. The robot 1 has set therein a coordinate system (hereinafter referred to as a robot coordinate system) Σb fixed on the robot base and a coordinate system (hereinafter referred to as a mechanical interface coordinate system) Σf fixed on the tool mounting surface 32. In the robot control unit 5, the position and the posture (current position) of the origin of the mechanical interface coordinate system can be determined at any time. Also, a well-known teaching operation panel 18 having manual operation keys is connected to the robot control unit 5, so that the operator can manipulate the robot 1 by operating the manual operation keys.
When determining the position of the forward end point 31 (tool center point) of the tool 30 by a touch-up method, a touch-up pin 6 having a sharp tip, for example, is prepared and fixed at a position within a range reachable by the center point of the tool 30 of the robot in operation. As a result, the tip of the touch-up pin 6 corresponds to one point fixed in space. By operating the manual operation keys of the teaching operation panel 18, for example, the tool center point 31 is touched to the touch-up pin 6 at different postures (for example, three or six postures) while jogging and, based on the robot position (position and posture of the mechanical interface coordinate system) at the time of each touch-up operation, the position of the tool center point 31 with respect to the tool mounting surface (represented by the mechanical interface coordinate system) 32 of the robot 1 is determined.
This method, however, poses the following problems:
(1) As described above, at the time of the touch-up operation, the robot is jogged while the tool center point of the robot is aligned to coincide with the forward end of the touch-up pin. In the process, the accuracy of the position of the tool center point finally determined is liable to be varied depending on the degree of skill of the operator with regard to positioning the robot.
(2) Also, this positioning operation is performed visually, and therefore even a skilled operator can produce only a limited accuracy.
(3) Further, in view of the fact that the tool center point is set in extreme proximity to the forward end of the touch-up pin, the tool center point is liable to contact the forward end of the touch-up pin and damage the tool or the touch-up pin.
Under the circumstances, there exists no publications describing a technique capable of solving these problems by a simplified method.
Accordingly, it is an object of this invention to solve the problems of the prior art, and to provide a measuring system whereby the position of the tool center point with respect to the tool mounting surface can be determined with high accuracy without using the touch-up pin.