1. Field of the Invention
The present invention relates to a robot with a camera, which has a camera for confirming a work as an object to be assembled.
2. Description of the Related Art
In general, image sensing conditions of a camera necessary for image processing include that there is no blur due to a vibration and that there is reproducibility of a position of a subject on the taken image, i.e., that a relative position between camera coordinates and coordinates at which the subject exists is grasped.
If a shutter speed is simply increased as a countermeasure against vibration, there is a problem of a decrease in imaging sensitivity due to insufficient light amount. In particular, the problem becomes conspicuous when an aperture stop of a lens is decreased for increasing a depth of field (range in the depth direction in which focus is obtained).
For instance, as a countermeasure against vibration when a camera is mounted on a robot arm, which is common in an FA field of automatic assembling recent years, there is known a method of releasing a shutter after vibration settling prospective time has passed (see Japanese Patent Application Laid-Open No. 2001-252883).
As a general countermeasure against vibration of a camera itself, there is known a technology of calculating an angular velocity from the integral of an angular acceleration sensor in the XY plane (e.g., an inertial force to a gyroscope), and enabling shutter operation if the calculated value is a threshold value or smaller (see Japanese Patent No. 2603871). It is supposed that the angular velocity is represented by W, and a rotation radius from the center of vibration to an arbitrary point F is represented by R. Then, a velocity of the point F is expressed as V=RW.
If a camera is mounted on an assembly robot, the following problem may occur. Hereinafter, for deeper understanding of the present invention, a related technology of the present invention is described with reference to the attached drawings. For instance, FIG. 7A illustrates an arm of a 7-axis vertical articulated robot (robot arm) including a J7 axis 107 for turning a wrist, a J6 axis 108 for a lower arm, and J1 to J5 axes (not shown). A hand 106 is mounted on the tip of the J7 axis 107, and a camera 101 is mounted via a camera supporter 102 on the hand 106 at its base portion. A tip portion of the hand 106 is constituted of fingers 104 for grasping a work 112. Assembling of the work 112 is performed using an image processing portion 109 for processing images of the camera 101 and a program for assembling written in a control portion 110 of the robot.
The camera 101 searches for the work 112 by an image processing method such as pattern matching, and a result thereof is used for the fingers 104 to grasp the work 112. A point F to be a reference in camera coordinates (Xc, Yc, Zc) is provided on the finger 104, and a position of the point F is recognized by the image processing method such as the pattern matching in the broken line illustrated in FIG. 7B.
It is supposed that the hand 106 is moved by a “trapezoidal” velocity instruction Vcm between start point Ps and end point Pe as illustrated in FIG. 6 in the order of stop, acceleration move, constant rate of move, deceleration move, and stop in the robot with a camera. Then, mainly because of an influence of mechanical elasticity of the 7-axis mechanism, the hand 106 is vibrated, resulting in an overshoot at the end of the acceleration and an undershoot at the end of the deceleration. If the vibration of the undershoot remains, relative positions of the point F and the work vary so that it is difficult to perform precise image processing. For easy understanding of description, it is supposed that the start point Ps and the end point Pe are on the X axis of the robot coordinates (X, Y, Z, Xm, Ym, Zm).
FIG. 5 is a graph illustrating a relationship between undershoot and shutter chance. As a countermeasure against vibration due to the undershoot, it is conceivable to wait until the vibration of the robot is settled sufficiently without permitting release of the shutter, and to release the shutter based on a detection signal after detecting that the vibration has been settled sufficiently. In other words, the shutter can be released after “waiting” vibration settling prospective time WT for a real position Pn from a start point at end time to of a positional instruction Pcm illustrated in FIG. 5. However, an adverse effect may be caused in industrial production, which includes an increase in assembly tact time. The vibration settling prospective time WT may be approximately one second, and float time WTs from the start point at time t7 when the vibration is actually settled is included in many cases. In this way, because of waiting for vibration settling, there is wasted time before releasing the shutter.
A time slot after passing of the vibration settling prospective time WT is indicated by a black band in the line of “6 PASSING OF TIMER WT” in the upper part of FIG. 5. The shutter is released at time t8 indicated by a small circle at the head of the black band.
The vibration settling prospective time WT varies in accordance with a movement stroke of the arm. Therefore, in a pick and place application in matrix, the stroke varies every time. For that reason, it is necessary to anticipate the float time WTs for vibration settling corresponding to a maximum vibration, which may cause more wasted time.
As a countermeasure against vibration of a camera itself, it is conceivable to release the shutter when the angular velocity is low, so as to suppress the vibration. In this case, a position of a specific point of the subject in the taken image is not secured. Therefore, this method cannot be applied to an assembly robot as it is.