Apparatus for fetching component parts

An apparatus for fetching a component part, with the apparatus including a finger unit pivotally supporting a plurality of fingers adapted to catch a component part. A first detection unit detects a catch of a component part and a first drive opens or closes the fingers. A holding unit swingably supports the finger unit and has a slider which is slidable in a horizontal direction by a drawback force. A second detection unit detects the slider at an end of the sliding motion. A moving unit supports the holding unit and moves the holding unit at least in the vertical direction by a second drive. A drive control is provided for controlling the first and second drives in accordance with signals produced by the first and second detection units so as to enable a catching of the component part.

The present invention relates to an apparatus for fetching automatically 
one or more component parts which are placed at random positions and in 
random attitude. 
Conventionally, vibratory parts feeders have been used widely for fetching 
component parts placed in bulk at random to the specified location. 
However, vibratory parts feeders have problems such as large dependence on 
the shape of parts handled by the feeders, improperness of use for large 
dimensional parts and damageable parts, and unavoidable noise. 
In order to solve these problems, methods using artificial vision are under 
study. In such methods, component parts placed in bulk are recognized as 
images by use of a television camera or the like, the images are analyzed 
by a processor such as a computer so as to determine the component part to 
be fetched (a component located at the upper portion of the bulk), and 
then the fetching apparatus is controlled based upon the result of the 
analysis. This system, however, needs a very expensive image sensor and 
processor, and therefore, at present, it is not practical. 
Accordingly, it is an object of the present invention to provide a parts 
fetching apparatus which avoids the problems encountered in the 
conventional vibratory parts feeders, and is inexpensive in construction. 
In accordance with the present invention an apparatus is provided which 
comprises a finger unit with a sensor means for sensing a catch of a 
component part, a holding unit which supports the finger unit and turns 
the finger unit when the finger of the unit comes in contact with a part, 
with the holding unit having a sensor means for sensing the turning 
operation. A moving unit supports the holding unit and moves it (along 
with the finger unit) at least on a vertical plane with respect to 
component parts, and a drive controller controls the movement of the 
moving unit and finger unit based on the signals from the sensors so as to 
search for a work piece which can be fetched and catch the part piece.

One embodiment of the present invention will now be described with 
reference to the drawings. 
Referring now to the drawings wherein like reference numerals are used 
throughout the various views to designate like parts and, more 
particularly, to FIG. 1, according to this Figure, fingers 2 and 4 are 
pivoted by pins 3 and 5, respectively, on finger unit 1. The finger 2 has 
a worm gear 6 fixed thereon through the pin 3, and the finger 4 has a worm 
gear 7 fixed thereon through the pin 4. The worm gears 6 and 7 are in 
engagement with a worm 8 fixed on the drive shaft of motor 9 which is 
mounted on the finger unit 1. A microswitch 10 is provided at the bottom 
of the finger unit 1. 
The finger unit 1 is pivotally mounted on slider 12 through a pin 13. The 
slider 12 is mounted on slide rail 14 which is fixed on holding unit 11 so 
that it travels along the rail 14, and the slider 12 is connected to the 
holding unit 11 through extension springs 15 and 16. Microswitches 17 and 
18 are provided on the holding unit 11. 
The holding unit 11 is fixed on rack unit 19 which is driven in the 
vertical direction by motor 20 with a rotation detector. The rack unit 19 
is mounted on slide base 22 through a bracket 21, and the slide base 22 is 
mounted movably on slide rail 25. The slide rail 25 has one end fixed to 
pole 24 and another end fixed to guide end 23. The slide base 22 is 
internally threaded so that it is moved in the horizontal direction by 
feed screw 26 which is driven by motor 27 with a rotation detector. 
As shown in FIG. 2, a drive controller 30 includes a detection unit 31, a 
logical determination unit 32, a data storage unit 33, and a drive unit 
34. 
Wiring is made for the controller 30 so that the signal from the 
microswitch 10 in the finger unit 1, the signals from the microswitches 17 
and 18 in the holding unit 11, and signals from the motor rotation 
detectors 20 and 27 in the moving unit are entered to the logical 
determination unit 32 through the detection unit 31. Wiring is made so 
that the output signals from the logical determination unit 32 are sent to 
the drive unit 34 to thereby drive the motor 9 for the fingers and the 
motors in the moving unit. Further, wiring is made so that data is 
transferred between the data storage unit 33 and the logical determination 
unit 32. 
In FIG. 3a, the finger 2 is in contact with a part piece 40 at point P. 
Normal m at the point P on the part surface and line l connecting the 
point P and the center of the pin 13 are assumed to make an angle of 
.theta.. Further assumption is made in FIG. 3a that .theta. is larger than 
.theta..mu., where .theta..mu. denotes the friction angle between the 
finger tip and the part piece, and it is expressed by the friction factor 
.mu. as .theta..mu.=tan.sup.-1 .mu.. In this case, the tip of the finger 2 
slides on the surface of the part piece 40, and if the holding unit 11 is 
further lowered, the finger unit 1 swings around the pin 13 to enclose the 
part piece 40, and then the microswitch 10 provided at the bottom of the 
finger unit 1 comes into contact with the part piece 40 as shown in FIG. 
3b. Catching of the part piece is recognized by the signal produced by the 
microswitch 10. 
FIG. 4a shows the case where the initial contact angle .theta. is smaller 
than .theta..mu.. In this case, the tip of the finger 2 does not slide on 
the top surface of the part piece 40, and if the holding unit 11 is 
further lowered, the finger unit 1 swings around the point P and at the 
same time the slider 12 moves rightward, causing the angle between the 
normal m and the line l to become .theta.' as shown in FIG. 4b. The 
friction factor between the slider 12 and the slide rail 14 is considered 
to be far smaller than that between the finger 2 and part piece 40, and it 
is neglected. When .theta.' becomes larger than the friction angle 
.theta..mu., the finger 2 is no longer held by the friction force at point 
P, and it slides on the top surface of the part piece 40 by being pushed 
back by the extension spring 16 as shown in FIG. 4c. If the holding unit 
11 is further lowered, the microswitch 10 comes in contact with the part 
piece 40 as shown in FIG. 4d. 
FIG. 5a also shows the case where the initial contact angle .theta. is 
smaller than .theta..mu.. The finger unit 1 swings around the point P and 
the slider 12 moves rightward, producing a contact angle of .theta.' as in 
the case of FIG. 5b. However, the slider 12 operates the microswitch 18 
before .theta.' becomes larger than .theta..mu.. Then, the falling 
operation for the holding unit 11 is stopped, and the moving unit is 
controlled so that the holding unit 11 is once lifted and moved toward the 
finger 2 (i.e., toward the part piece 40) by a certain distance as shown 
in FIG. 5c. After that, the holding unit 11 is lowered until the 
microswitch 10 comes into contact with the part piece 40. 
FIG. 6a shows the case where the initial contact angle .theta. is larger 
than .theta..mu., and in this case the top surface of the part piece 40 
has the opposite inclination as compared with the case of FIG. 3a. In this 
case, the finger unit 1 swings away from the part piece 40 as the holding 
unit 11 is lowered. If the holding unit 11 is further lowered, the finger 
unit 1 is directed to adjacent part piece 41. 
The following describes the control operation of the drive controller 30 
with reference to the flowchart shown in FIG. 7. 
Above part pieces, there are a plurality of preset points at which the 
holding unit 11 starts to descend, and the decent point is updated by 
operational step 50 in the flowchart. In step 51, the holding unit 11 
(i.e., the finger unit 1) is moved to the current descent point, and the 
unit is lowered in step 52. 
During the descent operation, the states of the microswitches 10, 17 and 18 
are monitored, and when the operation of a microswitch is detected, the 
control sequence at step 53 branches off through flow .circle.3 to step 
57 in which the descent operation is halted. 
If the operation of a microswitch is not detected in step 53, the 
operations of flow .circle.2 are repeated cyclically until the arrival 
of the finger unit 1 at the bottom of the parts box is detected in step 
54. When the finger unit 1 reaches the bottom of the parts box, the 
descent operation is halted in step 55 and the finger unit 1 is lifted in 
step 56. The control sequence returns to the start point .circle.1 , and 
the descent start point is updated in step 50. Then, the finger unit 1 is 
lowered again until the operation of a microswitch is detected in step 53. 
After the control sequence has branched through the flow .circle.3 to 
step 57 in response to the detection of the operation of a microswitch and 
the descent operation is stopped, it is checked whether the microswitch 
which has operated in step 50 is the microswitch 10 located at the bottom 
of the finger unit 1 or the microswitch 17 or 18 provided on the holding 
unit 11. 
If it is determined that a part piece 40 is touched not by the bottom 
portion of the finger unit 1, but by the tip of a finger, it is memorized 
in step 59 which finger has touched the part piece 40. Then, the finger 
unit 1 is lifted in step 60, and the holding unit 11 is moved in step 61 
in the direction corresponding to the finger which has touched the part 
piece 40. The control sequence returns to point .circle.2 and repeats 
the cyclic operations. 
If a part piece is touched by the bottom portion of the finger unit 1, the 
control sequence in step 58 branches off to step 62 in which the part 
piece 40 is caught, and then it is transported and released at the 
fetching place in step 63. These operations (the branch cycle from step 64 
to the start point .circle.1 are repeated, and when all part pieces are 
carried, the control sequence reaches the end point (step 65). 
It is apparent from the foregoing structure and operation that the 
inventive apparatus does not employ an expensive vision device and its 
processor, but works to detect the presence of part pieces 40 and their 
spatial relationship by using simple contact sensors (e.g., 
microswitches), resulting in a lower manufacturing cost and yet higher 
operational realiability. This facilitates the maintenance activity and 
provides superior durability. 
As described above, the present invention realizes an inexpensive and 
reliable parts fetching apparatus by the provision comprising a finger 
unit 1 with a plurality of fingers and having means for detecting a catch 
of a part piece 40, a holding unit which supports the finger unit 1 and 
turns the finger unit 1 by the drawback force when a finger of the unit 
comes in contact with a part piece and has means for detecting the turning 
operation, a moving unit which supports the holding unit and moves it at 
least on a vertical plane, and a drive controller which controls the 
moving unit 1 and finger unit in accordance with the signals from the 
detection means so that a part piece 40 is caught.