WO1984004723A1

WO1984004723A1 - Robotic systems utilizing optical sensing

Info

Publication number: WO1984004723A1
Application number: PCT/US1984/000570
Authority: WO
Inventors: Gerardo Beni; Susan Hackwood; Lawrence Anthony Hornak; Janet Lehr Jackel
Original assignee: American Telephone & Telegraph
Priority date: 1983-05-27
Filing date: 1984-04-16
Publication date: 1984-12-06
Also published as: IT1176215B; IT8421112A0; IT8421112A1; USH65H; EP0144345A1; EP0144345A4; JPS60501451A

Abstract

Two opposing fingers (30, 32) of a robot hand are each provided with an array (36, 40) of optical devices in optical communication with one another across the gap between the fingers. One finger is provided with an array of light emitters (31e) and the other is provided with an array of light receptors (31r), each of the light emitters being coupled, on a one-to-one basis, with each of the light receptors. An object (29) between the fingers blocks light transmission between different ones of the emitter-receptor pairs, whereby various information about the object, e.g., its shape, position and/or movement, can be detected.

Description

ROBOTIC SYSTEMS UTILIZING OPTICAL SENSING

Background of the Invention

This invention relates to robotic systems incorporating optical sensing.

Optical sensing of objects to be manipulated by robot mechanisms are known. However, most of the current optical systems, as described by R. P. Kruger et al, Proceedings of the IEEE, Vol. 69, p. 1524 (1981), use static overhead cameras placed above the robot working area. This static arrangement has the advantage of decoupling the calculation of position and orientation of the object from the robot motion. The robot is not slowed down by the vision system, which operates independently. This static arrangement, however, has a major drawback. The vision system is ineffective when it is most needed; i.e., when the robot is about to manipulate a part, since the robot arm blocks the field of view of the camera placed above the robot working area. To overcome this problem, camera-in-hand systems have been proposed and implemented. This method has the advantage of never hiding from the camera the part to be acquired. However, the robot must stop its motion to allow the camera to process the image and calculate position and orientation of the part. Recently this problem has been alleviated by using a low-resolution camera, see, C. Loughlin, Sensor Review, Vol. 3, p. 23 (1983), rigidly fixed to the robot gripper. However, the use of a camera to directly observe the object to be manipulated imposes severe requirements on the size of the camera, its mounting, and the ambient lighting and background to enable the camera to properly detect the object. Summary of the Invention

Two opposing fingers of a robot hand are each provided with an array of optical devices in optical communication with one another across the gap between the fingers. One finger is provided with an array of light emitters and the other is provided with an array of light receptors. An object between the fingers blocks transmission of light from some of the emitters to corresponding receptors, so that as the robot hand is moved, the signals from the receptors provide information as to the shape of the object.

Alternatively, the arrays of optical devices are mounted, for example, on a table top, and the robot may be used to move the object while it is disposed between the arrays. Brief Description of the Drawing

FIG. 1 is an enlarged isometric view of a robot gripper; PIG. 2 shows a T-shaped array-of optical devices mounted on the gripper; and

FIG. 3 is an enlarged side view of the sensor array of FIG. 1. Detailed Description With reference to FIG. 1 there is shown a robotic gripper 22 of generally known type. The gripper 22 includes a pair of fingers 30 and 32 slidably mounted on a palm member 28 so that the finger opposing faces 34 and 36 are maintained essentially parallel during opening and closing. Means for moving the gripper and for opening and closing the fingers are known.

In this embodiment of the invention, the finger 30 is provided with an array 40 of light emitters, and the finger 32 is provided with an array 42 of light receptors. The emitters may be active elements (such as

LEDs or junction lasers) or passive elements (such as light guides). Likewise, the receptors may be active elements (such as photodiodes) or passive elements (such as light guides or lenses), in either case, the array 40 emits a pattern of light beams 41 according to the geometric layout of the emitters. The receptor array has a corresponding layout so that there is a one-to-one relationship between emitters and receptors. In addition, the emitters are adapted to generate colli ated, parallel beams so that each beam is detected regardless of the position or motion of the fingers. This sensor array operates by detecting the presence and shape of an object 29 between the fingers. Illustratively, the object is depicted as a header for a semiconductor device. When positioned between the fingers, the object interrupts or blocks one or more of the parallel beams that pass between the fingers causing a change in the detected image displayed on camera 50 (or other suitable display) .

Where higher speed processing is desired, each array includes at least two non-parallel linear sets of devices. Typically, the linear sets are at right angles to one another in a U-shaped or T-shaped pattern.

A more specific description of the illustrated embodiment of the invention is now provided.

The arrays 40 and 42 each includes three linear sets of lenses which are cjraded refractive index (GRIN) rods well-known in the optics art as described by

C M. Schroeder, Bell System Technical Journal, Vol. 57, p. 91 (1978). The U-shaped array (FIG. 1) is disposed around the periphery of the fingers so that on each finger one linear set is located along one side, another linear set is along a parallel side, and the third linear set is along the bottom which connects the two sides. Each set can comprise, for example, 12 elements. Alternatively, a T-shaped array (FIG. 2) may be used on the fingers. To avoid contact between the object and the vertical set, the latter is disposed in a groove 51 in the surface of the robot finger.

The array 40 of GRIN rod emitters is coupled via optical fiber cable 62 to light source 60, e.g., a laser, and the array 42 of GRIN rod receptors is coupled via optical fiber cable 64 to camera 50. The optical signal on cable 64 is analyzed by the camera 50, and the output of the camera is used by a computer to control the robot in accordance with known techniques; see, e.g., the aforecited Loughlin article..

As s&own- in EϊG. 3, an optical fiber 33e is connected to the back of each lens 31e (only three lenses of each array being shown for simplicity) . The lenses collimates t&e light 41 across the gap between the fingers. A corresponding array 42 of GRIN rod lenses 31r is disposed on the other finger 32. These lenses 31r of array 42 are attached to fibers 33r which form the output cable 64. GRIN rod lenses have a parabolic refractive index distribution, as shown by light ray path 43, which produces collimated light beams 41 over a distance of about 5 cm.

The fibers of output cable 64 terminate in a common plane and are disposed, by known means, in a fixed array, thus providing, in effect, a screen or viewing area of small (the fiber ends) light sources. This viewing area or screen is viewed, to obtain the signal generated by the described sensor arrangement, by a video camera. For faster processing time, the viewing can be accomplished using a CCD or photodetector array. In fact, a linear CCD array can be used as an active receptor in lieu of the array 42 of GRIN rod receptor lenses. This latter arrangement eliminates the need for the fiberoptic connection between image sensing and image detecting. As mentioned, the detected image, indicative of the movement of the contours or edges of the object past the sensor element pairs, is utilized by a computer, in known fashion, to determine the position of the object relative to the gripper fingers. The described sensor can be regarded as an extreme case of low resolution vision. Although based on a relatively small number of sensing elements (e.g. 36) , the resolution can be comparable to or even higher than commercially available camera systems. Finally, as mentioned previously, the sensor may be mounted on, for example, a table top and a robot (or other mechanical apparatus) may be used to move the object in the gap between the arrays. Thus, the sensor is fixed but the robot motion is used to scan the arrays. This type of application requires that the robot computer is programmed to know the exact position of the robot hand at all times so that for each such position it can correlate the sensor data and thereby determine the position of the object in the robot gripper. This approach, however, is not preferred inasmuch as the robot gripper partially blocks the light beams when it is between the arrays.

OMPI

Claims

1. A robotic system comprising movable fingers (30, 32) characterized by an array (40) of light emitters on one of said fingers and an array of (36) light receptors on another of said fingers, each of said emitters being in optical communication on a one-to-one basis with each of said receptors, and means (50) for detecting the light pattern detected by said array of receptors for determing the position of an object disposed between said fingers.

2. The robotic system of claim 1 wherein each of said arrays includes at least two non-parallel linear sets of devices.

3. The system of claim 2 wherein said linear sets of devices are located along the periphery of said fingers.

4. The system of claim 3 wherein said fingers each has a surface which is used to contact said object and said arrays are recessed within said surface.

5. The system of claim 4 wherein said surfaces are maintained essentially parallel to one another during motion of said fingers.

6. The system of claim 5 further wherein said emitter devices comprise GRIN rod lenses coupled to a light source and said receptor devices comprise GRIN rod lenses coupled to a light detector.

7. The robot of claim 4 wherein said linear sets are oriented to form a T-shaped pattern.

8. The robot of claim 3 wherein said linear sets are oriented to form a U-shaped pattern.

OMPI