Optical fiber gripping and positioning apparatus

The apparatus uses a gripper mounted on a moveable arm to pick up an optical fiber at a pickup location, with the free end of the optical fiber extending from the gripper. The arm is moved to position the free end generally in the region of the target location, but slightly displaced therefrom. An image of the region of the target location is obtained from a camera directed to receive the image, where the region is backlit by diffused light from a light source. Where the target is a component on a translucent substrate, the substrate may act as the diffuser for the light source. The image from the camera is analyzed to determine the position of the free end in relation to the target location, and the arm is moved to accurately position the free end at the target location based on the determination of relative positions. The gripper has a downwardly-opening inverted V-shaped groove running longitudinally, to which a vacuum is supplied.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to equipment for handling and placing optical 
fibers. 
Optical fibers are used commonly for transmission of digital data because 
they are capable of transmitting high volumes of data due to their large 
bandwidth. The fibers and components to which the fibers must be connected 
for functionality are very small and therefore difficult to easily 
manipulate and work with. An optical fiber might be only 80 microns in 
diameter, and components such as transmitters, receivers and transducers 
might not be more than 100 microns in typical dimensions. 
Given the precision required for handling and connecting optical fibers to 
components, use of robots in the process results in higher-quality end 
products and reduces the rejection rate of the assembled equipment. 
However, because of the small dimensions of an optical fiber, automation 
of the handling and positioning of the fiber has always posed considerable 
difficulty. 
2. Description of the Prior Art 
There are a number of types of devices currently available for handling 
optical fibers, three of which are discussed below. 
The first type uses an upwardly-opening groove, into which the fiber is 
placed. A "lid" is then placed over the optical fiber to hold the fiber 
firmly between the lid and the groove. In the closed state, the lid must 
be mechanically locked into position. 
The second type is similar in concept to the first type. A groove is 
provided in a simple cylinder. The optical fiber is pushed into the 
groove, so that the fiber sits below the outer circumference of the 
cylinder. A cover, such as a sheath, is placed over the cylinder to 
prevent the optical fiber from slipping out. 
Both of the above types of devices apply mechanical pressure to the fiber 
in order to hold the fiber in place. The mechanical pressure however may 
damage the fiber and potentially change its optical characteristics. Also 
both types strongly depend on the diameter of the optical fiber in order 
to secure a hold on the fiber. Automating these grippers is difficult for 
a variety of reasons, including relative bulkiness, the need of a human 
operator to place the fiber into the gripper, the weight of the grippers, 
and the gripper size relative to the placement accuracy needed. 
The third type of device involves soldering or welding a T-shaped or 
L-shaped "handle" to the fiber. A gripper can then pick, orient, and place 
the fiber by moving the handle. This requires applying heat to the end of 
the optical fiber to attach and detach the handle, increasing the risk of 
damage to the fiber. During the removal phase, the fiber may move, thereby 
reducing the quality of the finished product. 
The invention uses a vacuum gripper, as will be described in greater detail 
later. Vacuum has been used previously by stationary grippers to hold an 
optical fiber steady, as disclosed in U.S. Pat. Nos. 5,135,590, 5,386,490, 
and 5,185,846, for example, but vacuum does not appear to have been used 
in a moveable gripper to grip, move and position an optical fiber. 
Apart from the difficulty in handling optical fibers, determining the 
fiber's position with precision is also difficult. To properly connect the 
optical fiber to a component, accurate positioning and position 
determination are both essential, if reject rates are to be kept at 
acceptable levels. There is therefore a need for apparatus which can 
effectively grip the fiber, determine its position, and move it precisely 
to the desired position. One of the most common methods of determining 
position for automation purposes is to use a vision system to capture and 
analyze an image of the fiber by standard image processing software. 
However, because the fibers are largely transparent under normal direct 
illumination, they are more or less invisible to a camera, even with 
normal contrast enhancement. The image which may be obtained from them 
does not have sufficiently sharp defining lines to be used by the image 
processing software. There is therefore a need to provide sufficient 
contrast to enable the vision system to capture an image which permits the 
position of the fiber to be readily ascertained. 
SUMMARY OF THE INVENTION 
In view of the above, it is an object of the invention to provide a system 
which is capable of holding an optical fiber, determining the position of 
the end of the fiber in relation to a target location, and transporting it 
to the target location with high precision. 
It is a further object of the invention, in the context of such a system, 
to provide a gripper which is able to lift and hold the optical fiber 
efficiently and without damage. 
In the invention, the system uses a gripper which has a downwardly-opening 
groove, preferably V-shaped, running longitudinally, to which a vacuum is 
supplied. 
The gripper is carried by a movable arm, which is used to pick the optical 
fiber from a pickup location and to move it to the area of the target 
location. A vision system, using a camera and image analysis software, 
determines the location of the end of the optical fiber in relation to the 
target, in the X-Y plane, the location of the target and of the optical 
fiber in the Z or height plane already being known. The detected location 
of the end of the optical fiber in relation to the target determines what 
movement of the arm is required to move the end of the fiber to the target 
location. 
To permit the vision system to see the end of the optical fiber, diffused 
back lighting is used. In one application, where the target is a component 
mounted on a translucent substrate, the substrate acts as the diffuser for 
the light source. The diffused back-lighting provides sufficient contrast 
for the image captured by the camera to be analyzed to determine the 
position of the end of the fiber. 
Further features of the invention will be described or will become apparent 
in the course of the following detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1 and 2 shown the main components of the system. A gripper 1 has a 
tip 2 which holds an optical fiber 20 near its end 21, for positioning 
adjacent a target location 3, in this case on a component 4 mounted on a 
substrate 5. The gripper could be used in any other operation where 
precise positioning of the end of the fiber is important. A light source 6 
is provided underneath the target location, and is diffused by the 
substrate to provide sufficient contrast for the image to be analyzed to 
determine the position of the end of the fiber. In other embodiments such 
as where there is no intervening substrate, the desired diffusion could 
obviously be provided by other means. A camera 7 is located so as to view 
the target area and the end of the optical fiber from above. 
Because an optical fiber is mostly translucent, an accurate image of the 
tip or the edges of the fiber is difficult to obtain. However, for 
automating the process, it is essential to be able to obtain clear 
positional information for the tip and edges of the fiber. 
The diffused light source both provides the light for the camera and the 
illuminated backdrop against which the camera takes the image of the 
fiber. The tip and the edges of the fiber appear as shadows to the camera 
because the optical fiber acts as a lens and concentrates or diffuses the 
light passing through it toward the center of the fiber. 
Here the importance of the diffuse light source becomes apparent, as 
otherwise the contrast would not be as pronounced. First, the diffused 
light source, acting as an illuminated backdrop, accentuates for the 
camera and the image processing unit the lines defining the fiber's 
shadow. Second, it is generally true that the an object's edge bends some 
of the light passing in its vicinity, resulting in a halo effect which is 
commonly seen when a picture of an object against a light source is taken. 
However, the more diffused a light source is, the less pronounce this 
effect. Therefore, by using a diffused light source, the contrast between 
the shadowed edges and the illuminated background becomes very pronounced. 
This strong contrast results in the ability to obtain a sharp line 
defining the optical fiber's edge or tip for use in the image processing 
unit, which tries to determine the position of lines in an image. 
Because of high definition obtained as a result of the use of diffused 
light source, the position of the tip of the fiber may be determined with 
better than 1 micron accuracy. 
As seen in FIG. 2, the gripper 1 is attached to the end of a robotic arm 8. 
The arm is capable of positioning the gripper and the fiber in a precise 
manner, such that in combination with the accuracy of the vision system, 
it is possible to ensure that the end of the optical fiber is positioned 
to within less than one micron of the location of the target. 
FIG. 1 shows the camera schematically, but in FIG. 2 it can be seen that 
for space reasons it is preferable to orient the camera differently, and 
to use a mirror 9 to permit this. 
FIG. 3 shows the operation of the system in an end view. The gripper is 
moved to a pickup tray 10, where it is brought into close alignment with 
an optical fiber near its end. The pickup tray has previously been loaded, 
manually or automatically, with an optical fiber. The configuration of the 
pickup tray is such that the fiber is automatically aligned properly for 
pickup, but the end 21 of the fiber does not need to be precisely 
positioned. Vacuum is then applied, to capture the optical fiber. It is 
then transported by the gripper to the area of the camera, so that its 
precise location in relation to the target may then be determined, prior 
to final positioning. 
Conventional image analysis software determines the location of the end of 
the optical fiber in relation to the target, in the X-Y plane. Due to 
previous calibration of the height of the gripper tip in relation to the 
height of the substrate, the location of the target and of the optical 
fiber in the Z or height plane is already known, and does not need to be 
determined by the vision system. The camera preferably is generally 
perpendicular to the fiber and the diffused light source, so that parallax 
errors can be discounted, but the camera clearly could be positioned off 
the center line as long as appropriate error correction is implemented in 
the software. 
Once the position of the end of the fiber in relation to the target has 
been determined, the arm 8 transports the optical fiber to the correct 
target position for the soldering, fusing, or other necessary operation to 
be carried out. 
Details of the gripper are shown in FIGS. 4-6. It should be appreciated 
that the dimensions of the gripper are quite small. The preferred 
embodiment of the gripper has approximate dimensions of 
1".times.1".times.1/2", making the gripper an easy tool to control and 
therefore use in automation. Of course, the dimensions may be made smaller 
or larger, depending on the application. While the preferred embodiment is 
made of metal, it could instead be made of other material such as plastic 
or elastomers. 
The bottom of the tip has two angled surfaces 11 which define a shallow 
V-shape, to accommodate the optical fiber. Preferably, as shown in FIG. 5, 
the overall width of the bottom of the tip is comparable to the diameter 
of the optical fiber. A small air channel 12 passes up the center of the 
tip, to a larger air channel 13, which eventually leads to a plenum 14 to 
which a vacuum hose 15 is connected. Since the size of the small air 
channel 12 is very small, it is desirable to open up to the slightly 
larger air channel 13 to minimize the pressure drop through the channels. 
In the preferred embodiment, the small air channel 12 is a slot which 
extends longitudinally along the front portion of the tip, and the larger 
air channel 13 is a corresponding slot. However, it should be clear that a 
number of vacuum holes could be used instead of such a continuous slot 
arrangement. All that is required is that sufficient vacuum be delivered 
to securely hold and transport the optical fiber. 
It should be clearly recognized that the V-shape is not strictly essential, 
although it is essential that there be surfaces against which the fiber is 
positively located by the vacuum. A U-shape, or a trough shape, or other 
similar shape could also be used, or a radius matched to the radius of the 
optical fiber could be used. 
The vacuum holds the fiber quite effectively, without applying mechanical 
force which might damage the fiber. The angled surfaces 11 help to orient 
the fiber, so that it is parallel to the tip. If desired, the gripper can 
be translated or rotated in any direction or about any axis, so that the 
fiber can be oriented in space in any desirable manner. 
It will be appreciated that the above description related to the preferred 
embodiment by way of example only. Other variations of the invention will 
be obvious to those knowledgeable in the field. For example, the invention 
may be made from other material or manufactured used different methods. 
The gripper in the preferred embodiment is made of two halves; however, it 
is also possible to make the invention from one piece or from more than 
two pieces put together. The diffused light source may be created by 
directing a light to partially reflective backdrop. Many other variations 
on the invention will be obvious to those knowledgeable in the field, and 
such obvious variations are within the scope of the invention as described 
and claimed, whether or not expressly described.