U.S. patent application number 09/750053 was filed with the patent office on 2001-10-04 for wire harness assembly line and wheeled worktables.
Invention is credited to Suzuki, Toshiaki.
Application Number | 20010026750 09/750053 |
Document ID | / |
Family ID | 18531553 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010026750 |
Kind Code |
A1 |
Suzuki, Toshiaki |
October 4, 2001 |
Wire harness assembly line and wheeled worktables
Abstract
Each of the wheeled worktables 1, which is isolated from the
others, travels self-dependently with drive of the motor M and the
sensor (optical recognition device) 5 is provided on each wheeled
worktable 1 while the optical recognition tape T as the recognition
object for the sensor 5 is attached to the predetermined conveyance
passage on the floor 11 for inducement of the wheeled worktables 1.
Since the modification of the conveyance passage to meet any need
of increase or decrease of the wheeled worktables is carried out
only by reattachment of the optical recognition tape T, the passage
can be modified into any form by a simple operation without
generation of useless spaces between the adjoining wheeled
worktables 1 and, without any mechanical restraint on the wheeled
worktables, replacement of the wheeled worktables 1 for any
increase or decrease in the wheeled worktables do not require such
labor and time for dismounting from and remounting on the chain as
in the case of the assembly line driven with the endless chain.
Inventors: |
Suzuki, Toshiaki;
(Nagoya-shi, JP) |
Correspondence
Address: |
Oliff & Berridge PLC
P.O. Box 19928
Alexandria
VA
22320
US
|
Family ID: |
18531553 |
Appl. No.: |
09/750053 |
Filed: |
December 29, 2000 |
Current U.S.
Class: |
414/234 ;
198/465.1; 414/232; 414/352 |
Current CPC
Class: |
H01B 13/01227
20130101 |
Class at
Publication: |
414/234 ;
414/232; 414/352; 198/465.1 |
International
Class: |
E04H 006/00; B65F
009/00; B65G 067/00; B65G 029/00; B65G 037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 2000 |
JP |
2000-002447 |
Claims
What is claimed is:
1. A wire harness assembly line where wire harnesses are assembled
while wheeled worktables are moved in sequence of processes;
comprising: each of said wheeled worktables which travels
self-dependently with drive of a motor while being isolated from
the others, and each of said wheeled worktables which includes a
sensor for travel along predetermined conveyance passage on a floor
while objects of recognition by said sensor are installed along
said predetermined route on said floor surface.
2. The wheeled worktable for use in the assembly line according to
claim 1, wherein on a bottom surface of said wheeled worktable, a
rectangle whose center line is parallel to a travelling direction
of the wheeled worktable is defined while an isosceles triangle
whose base and height are equal is defined in such manner that an
symmetry axis thereof overlaps the center line of said rectangle
with the base including a midpoint of said rectangle, said wheeled
worktable comprising: a driving wheel that has a steering function
disposed at a vertex of said isosceles triangle, and trailing
wheels that are securely disposed at both ends of the base in such
manner that the revolving surfaces thereof are always in a
direction parallel to the travelling direction of the wheeled
worktable.
Description
BACKGROUD OF THE INVENTION
[0001] The present invention relates to a wire harness assembly
line.
[0002] In the above-described wire harness assembly line, an
operation chart board for each of the processes is mounted on each
of wheeled worktables and conveyed to a operator's station in a
sequence of the processes, and the operator works sequentially on
the chart board to complete the product. FIG. 11 shows an example
of the conventional wheeled worktable conveyance line that is
driven with an endless chain.
[0003] As shown in the figure, a straight outbound passage 23 and a
straight return passage 24 are installed parallel as conveyance
passages of wheeled worktables 21 and both ends are connected with
turning parts 25 and 26 making a closed passage, wherein an endless
driving chain 22 is installed along the closed passage with the
aforenamed wheeled worktables linked with the chain 22 in the order
of the processes and moved in one direction with chain 22 driven by
a motor Mc. Operators m are shown respectively behind the wheeled
worktables 21 in the figure and each of the operators m assembles
parts on the operation chart board on the wheeled worktable 21 on
arrival of the wheeled worktable 21 at the position of the operator
m.
[0004] Both the turning parts 25 and 26 are simply places for
directional changes of the wheeled worktables 21, and no work is
done there. An entrance 27 for finished products from a previous
process is built on the outbound passage side of the turning part
26 while an exit 28 for the finished product in this assembly line
is built on the return passage side.
[0005] In such an assembly line, classified flow process operations
are carried out for efficient manufacturing of the wire
harnesses.
[0006] However, the following problems exist in the conventional
assembly line in the form as described above.
[0007] (1) In a case of change in production mode (production
amount or production model) as the object of line manufacturing,
the aforenamed wheeled worktables 21 need to be increased or
thinned out and, for this purpose, the above-described assembly
line form wherein the chain 22 is secured along the conveyance
passage of the wheeled worktables 21 requires a large scale of
remodeling of the transportation mechanism, through replacement or
cut of the chain 22 but the work requires a lot of human power and
stop of the assembly line for a long time.
[0008] It may be convenient if the conveyance passage is large
enough to allow any immediate increase in the wheeled worktables,
but this can cause increase in the pitch of spacing between the
wheeled worktables, which can results with decrease in conveyance
efficiency and accordingly with decrease in production
efficiency.
[0009] In case the wheeled worktables are thinned out under this
circumstance, the spacing pitch between the wheeled worktables
becomes the larger and the assembly line production efficiency
becomes the lower.
[0010] Moreover, this is a great loss in the aspect of the site use
efficiency.
[0011] (2) In a case of replacing only the wheeled worktables 21
for a reason of change in the model to be manufactured, even
without changes in the production amount as the object of
manufacturing and accordingly without increase or decrease in the
number of the wheeled worktables 21, the assembly line stagnates
greatly since it gives trouble and takes time to dismount from and
mount on the chain 22.
[0012] (3) In a case of loss in the chain 22 or a malfunction of
the drive motor Mc, it gives trouble and takes time for the
recovery, and, in general, it costs a lot for the repair.
SUMMARY OF THE INVENTION
[0013] Therefore, the invention is purposed to solve the
above-described problems in the conventional wire harness assembly
line, making the assembly line in the form that can afford any
change in the assembly line configuration on rise of any need for
change in the production amount and/or in such the production form,
such as the model, and that can afford the change without
troublesome operations and at low costs, with successful prevention
of any decrease in the assembly line conveyance efficiency, or
accordingly any decrease in the production efficiency.
[0014] To solve the above-described problems, the invention has a
structure wherein each of the wheeled worktables travels
self-dependently with drive of a motor while being isolated from
the others and wherein each of the wheeled worktables is equipped
with a sensor for travel along predetermined conveyance passage on
a floor while objects of recognition by the sensor are installed
along the predetermined route on the floor surface.
[0015] The structure enables assembly line change only with
replacement of the sensor recognition objects and rerouting of the
wheeled worktable conveyance passage. The recognition object of the
sensor is usually an optical recognition tape or a magnetic
recognition tape that is attached to a floor where the wheeled
worktables travel and that is easy to be attached and removed.
Since the conveyance route can be modified into any desired form
only by the tape replacement, an optimum rerouting that eliminate
every unnecessary space between adjacent wheeled worktables with
setting of a maximum conveyance efficiency (accordingly the
production efficiency) is available at any increase or decrease in
the wheeled worktable number. Moreover, the cost is small.
[0016] Additionally, such is a desirable configuration that a
rectangle whose center line is parallel to a travelling direction
of the wheeled worktable is defined on the bottom surface of the
wheeled worktable while an isosceles triangle whose base and height
are equal is defined in such manner that an symmetry axis thereof
overlaps the center line of the rectangle with the base including a
midpoint of the rectangle and by that a driving wheel that has a
steering function is disposed at a vertex of the isosceles triangle
while trailing wheels are securely disposed at both ends of the
base in such manner that the revolving surfaces thereof are always
in a direction parallel to the travelling direction of the wheeled
worktable. As shown in FIG. 6 below and FIGS. 8 through 10 as its
comparison examples, this configuration enables reduction of the
entire assembly line size since the turnabout of the wheeled
worktable at the turning part of the assembly line can be carried
out most efficiently with a small turn to result with reduction in
the space occupation at the turning part.
BREIF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1A is a front elevation, and FIG. 1B is a side view of
the wheeled worktable of the embodiment;
[0018] FIG. 2 is a modal drawing to show the basic production mode
of the assembly line of the embodiment;
[0019] FIG. 3 is a modal drawing to show a variation of the
embodiment in FIG. 2;
[0020] FIG. 4 is a modal drawing to show another variation of the
embodiment in FIG. 2;
[0021] FIG. 5 is a modal drawing to show a wheel layout of the
wheeled worktable of the embodiment;
[0022] FIG. 6A shows a wheel layout of the wheeled worktable and
FIG. 6B shows a locus thereof at the turning part;
[0023] FIG. 7 shows a locus at the turning part of a conventional
assembly line;
[0024] FIG. 8A shows a wheel layout and FIG. 8B shows a locus of a
variation for comparison with FIG. 6;
[0025] FIG. 9 is the same as the above;
[0026] FIG. 10 is the same as the above; and
[0027] FIG. 11 is a modal drawing to show the conventional wire
harness assembly line.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] The following paragraphs describe the embodiments of the
wire harness assembly line related to the invention. FIG. 1 shows
an embodiment as a wheeled worktable 1, wherein an entire body of a
wheeled base part 2 is formed with square pipes into a hexahedron,
which is provided with wheels 3 at the bottom and an operation
chart board 4 (an assembly chart board) on the upper surface.
[0029] As described later in detail, the wheels 3 consist of four
auxiliary wheels 3c that are installed in the four corners of a
rectangular bottom of the wheeled worktable 1 and a driving wheel
3m and two trailing wheels 3s that are installed at the center
part. The driving wheel 3m that is driven by a motor M that is
suspended from the bottom of the wheeled worktable 1 has a steering
function while rotational surfaces of the trailing wheels 3s are
always maintained parallel in the travelling direction
(longitudinal direction) of the wheeled worktable 1. The auxiliary
wheels 3c are designed only for stable support of the wheeled
worktable 1, and each of the rotational surfaces can rotate
360.degree. freely on a vertical axis.
[0030] On the top of the operation chart board 4, a wire harness W
in the process of assembling is mounted.
[0031] A sensor inducement system for travel of the wheeled
worktable 1 along the predetermined conveyance route is installed
between the above-described self-driven wheeled worktable 1 and the
floor 11 where it moves. As the sensor inducement system, a sensor
(an optical recognition device) 5 is mounted on the bottom of the
wheeled worktable 1 while an optical recognition tape T which is a
recognition object of the sensor 5 is attached to a surface of the
floor 11 along the predetermined conveyance route. The wheeled
worktable 1 whose sensor 5 recognizes the optical recognition tape
T is enabled to travel without deviating from the conveyance
route.
[0032] Thus, this wheeled worktable 1 is a self-travelling wheeled
conveyance worktable which travel automatically along the
predetermined route by the driving wheel 3m that is driven by the
motor M and the above-described sensor inducement system.
[0033] FIGS. 2 through 4 modally show a conveyance passage 12 and a
wire harness assembly line along which the wheeled worktables 1
travel, wherein, as shown in the figures, in the same manner as in
the case of the above-described conventional endless chain, a
straight outbound passage 13 and a straight return passage 14 are
provided parallel with both ends thereof connected to turning parts
15 and 16 making a closed passage, and wherein the aforenamed
optical recognition tape T is attached along the closed conveyance
passage 12.
[0034] White arrows 17 and 18 over and below the turning part 16 to
the right in the figures of the conveyance passage 12 indicate
incoming and outgoing of the products to this assembly line,
wherein the lower arrow 17 indicates incoming finished products
from the previous process of the assembly line while the upper
arrow 18 indicates outgoing finish products from this assembly line
to the next process.
[0035] The assembly line where the self-travelling wheeled
worktable 1 moves is different from the assembly line that is
formed through securing of the conventional endless chain 22 as
shown in FIG. 11 and the conveyance passage 12 can be changed into
any desired way only through replacement of the optical recognition
tape T on the floor 11. The replacing operation is not troublesome
and the tape T is inexpensive; therefore, in a case of increasing
or decreasing the wheeled worktables to meet a change in the
production mode (ratio of the production amount and the model), the
action can be taken instantaneously without elaboration. FIGS. 3
and 4 show modifications in the assembly line of the embodiment
that incorporates flexibility to changes, with the production mode
in FIG. 2 as a basic.
[0036] In the assembly line shown in FIG. 2, twenty wheeled
worktables 1, which are marked with signs (1) through (20), are
arranged on the conveyance passage 12, and three kinds of models A,
B and C are allotted and manufactured on these with the
manufacturing ratios of models in the assembly line are
respectively 50%, 25%, and 25%; that is, ten wheeled worktables 1
for manufacturing of Model A, five wheeled worktables 1 for
manufacturing of Model B and five wheeled worktables 1 for
manufacturing of Model C.
[0037] Since no operations, except turning, are carried out on the
wheeled worktables 1 at the turning parts 15 and 16 on the right
and left of the figure, which are marked with (10) and (20),
eighteen operators m are stationed along both of the straight parts
13 and 14 in the conveyance passage 12 of the wheeled worktables 1.
The operators m are shown only on one side of the wheeled
worktables 1 that are marked with (5) and (15) to avoid complexity
in the figure but they are actually stationed respectively in the
positions of all of the wheeled worktables 1 except the aforenamed
wheeled worktables 1 that are marked with (10) and (20).
[0038] Although the manufacturing models in FIG. 3 are the same A,
B and C as in the basic mode in FIG. 2 above and the ratios are
respectively the same 50%, 25% and 25%, the entire production
amount is reduced to 80% and the number of the wheeled worktables 1
is thinned out to sixteen, which is four wheeled worktables less
than in the basic mode; namely, eight wheeled worktables 1 for
manufacturing of Model A, four wheeled worktables 1 for
manufacturing of Model B and four wheeled worktables 1 for
manufacturing of Model C. The number of operators is reduced to
fourteen.
[0039] In this case of assembly line modification, although the
wheeled worktables 1 are thinned out by four wheeled worktables 1
to sixteen, since a simple operation can reduce the conveyance
passage 12, the sixteen wheeled worktables 1 can be disposed
without useless space between the adjacent, and thus the conveyance
efficiency is maintained for 100% without fall in the production
efficiency.
[0040] Similarly, in the assembly line shown in FIG. 4, although
the production amount and the number of the wheeled worktables 1
are the same as in the basic mode (twenty wheeled worktables 1 and
18 operators), the number of production models is increased with
addition of D to the three models A, B and C and the production
ratios change into 50%, 25%, 15% and 10%; namely, ten wheeled
worktables 1 for manufacturing of Model A, five wheeled worktables
1 for manufacturing of Model B, three wheeled worktables 1 for
manufacturing of Model C and two wheeled worktables 1 for
manufacturing of Model D.
[0041] In this case, the change in the assembly line is achieved by
replacement of the wheeled worktables 1 and, since each of the
wheeled worktables 1 is isolated from the others and induced to
travel along the conveyance passage 12 by the above-described
sensor inducement system at the time of travel, being totally free
from any mechanical restraint, such as linkage with the chain in
the case of endless-chain assembly line, the replacement involves
no troublesome operation, such as removal and reattachment of the
chain, and thus prevents the time loss for that much.
[0042] As described above, this embodiment enables construction of
the assembly line wherein the shape of conveyance passage 12 for
the wheeled worktables 1 can be changed into any desired form
without causing a fall in the conveyance efficiency and, in the
case of replacing the wheeled worktables 1, the wheeled worktables
1 can be increased and decreased without causing a time loss for
the replacement.
[0043] Moreover, in the case of the conventional chain drive, it
takes a lot of time and labor to recover from a trouble, such as
the chain cut or the drive motor breakdown, but, in the case of the
sensor inducement system like this embodiment, the breakdown of the
sensor itself occurs infrequently, and even a major breakdown is as
insignificant as soilage or damage on the recognition tape T, which
is repaired only by replacement of the tape T, which takes only a
short time and a little labor and expense.
[0044] Although the sensor inducement system in this embodiment is
of the optical recognition type and the recognition object is the
optical recognition tape, the sensor of a magnetic perception type
with use of a magnetic recognition tape as the recognition object
is also available.
[0045] Although the assembly line in this embodiment is
advantageous as described above and the problems of the
conventional endless chain are solved, the embodiment goes further
with reduction in the occupation area of the assembly line through
contrivance in the layout of the wheels 3 of the wheeled worktable
1. That is, of the three kinds of the wheels 3, which are the
driving wheel 3m, the trailing wheel 3s and auxiliary wheels 3c,
the layout of the driving wheel 3m and the trailing wheels 3s is
specified in a certain shape to minimize the turning locus at the
turning parts 15 and 16 of the conveyance passage 12. As described
above, the auxiliary wheels 3c are purposed only for stable support
of the wheeled worktable 1.
[0046] FIG. 5 modally shows the layout of the wheels 3 that are
provided on the bottom of the wheeled worktable 1 (wheeled base
part 2) in this embodiment. FIG. 6A is a sketch of the driving
wheel 3m and the trailing wheels 3s as an exclusive extract from
FIG. 5 and FIG. 6B shows the locus of the wheeled worktable 1 with
this wheel layout when turning at the right turning part 16 in the
above-described conveyance passage 12. Since the assembly line is
formed in a symmetrical shape, it is similar at the left turning
part 15.
[0047] FIG. 7 shows a locus of the wheeled worktable 1 with the
same external shape of the bottom when turning at the turning part
in the conventional assembly line that is driven with the endless
chain.
[0048] For further comparison, FIGS. 8 through 10 show the loci of
the wheeled worktables 1 of other embodiments together with
different wheel layouts (drawing A in each of the figures) when
turning at the same turning part 16 (the same as at the turning
part 15).
[0049] Since the external dimensions of the wheeled worktables 1
and their composition that auxiliary wheels 3c are provided in the
four corners are common to all the wheeled worktables 1, and the
four corners is common to all, each of the wheel layout drawings
(drawing A in each of the figures) shows only the driving wheel 3m
and the trailing wheels 3s. The following paragraphs describe on
the differences in the turning manners of the wheeled worktables 1
of the embodiment and the variations for the comparison.
[0050] As shown in FIG. 5, the wheeled worktable 1 of this
embodiment has a long side a of 2800 mm and a short side b of 800
mm, which is common to those of the variations for comparison in
FIGS. 8 through 10. The driving wheel 3m that has the steering
wheel function is provided at the position on the center line L
that is parallel to the long side a of the rectangle and at 600 mm
to the left in the figure from the midpoint o of the center
line.
[0051] The two trailing wheels 3s are provided on an orthogonal
line of the center line L, which crosses at the midpoint o of the
center line L, at symmetrical positions 600 mm apart on both sides
of the above-described center line L.
[0052] The trailing wheels 3s are securely disposed so that the
rotating sides thereof are always parallel to the longitudinal
direction of the wheeled worktable 1.
[0053] As shown in FIG. 6B, the turning locus of the wheeled
worktable 1 in FIG. 5 (and FIG. 6A) at the turning part 16 is
symmetric against the center line of the conveyance passage 12,
with equal shapes of warps on both the outgoing passage side 13 and
return passage side 14, which is the same as in the case of the
conventional endless chain drive shown in FIG. 7.
[0054] On the other hand, the one shown in FIG. 8 has a wheel
layout as shown in FIG. 8A, wherein the driving wheel 3m is
provided at the center o of the bottom of the wheeled worktable 1
while the two trailing wheels 3s are provided on a line that
crosses the center line L at a position 1000 mm apart to the right
in the figure from the above-described center o on the center line
L, at symmetrical positions 600 mm apart on both sides of the
center line L.
[0055] The turning locus of the wheeled worktable 1 at the turning
part 16 is as shown in FIG. 8B and, for a purpose of comparison
with the above-described FIG. 6B, the outer locus of the wheeled
worktable 1 in FIG. 6B is shown with a one-dot-one-dash line in
FIGS. 8B, 9B and 10B, with additional indication of a position
S.sub.6 for a shift of the wheeled worktable 1 from the straight
return passage 14 to the turning part 16 and position T.sub.6 for a
shift from the turning part 16 to the straight outbound passage
13.
[0056] As elucidated by the figures, the locus of the wheeled
worktable 1 in FIG. 8 occupies extra space that protrudes from the
circle, in comparison with the one-dot-one-dash line that shows
locus of the wheeled worktable 1 in FIG. 6.
[0057] The shift timing of the wheeled worktable 1 from the
straight return passage 14 to the turning part 16 is late since the
shift position S.sub.8 is on the downstream side of the position
S.sub.6 in the case of FIG. 6, and the shift timing from the
turning part 16 to the straight outbound passage 13 is also late
since the position T.sub.8 is on the downstream side of the
conveyance passage 12 compared with the position T.sub.6 in FIG. 6.
This shows that a quite useless space exists between the straight
part for assembly work and the turning parts of the wheeled
worktable 1. Thus, in addition to that the above-described turning
locus area is large, it is understood the wheeled worktable 1 in
the layout of FIG. 8 requires a larger space than the case in FIG.
6.
[0058] Similarly, the wheel layout of the one in FIG. 9 is as shown
in FIG. 9A, wherein the two trailing wheels 3s are disposed on an
orthogonal line that crosses the center line L at the center o of
the bottom and 600 mm apart symmetrically on both sides of the
center line L while the driving wheel 3m is disposed on the center
line L and at a position 1000 mm apart from the center o to the
left in the figure. The locus of the wheeled worktable 1 turning at
the turning part 16 is as shown in FIG. 9B.
[0059] Compared with the locus of the wheeled worktable 1 in FIG.
6, which is shown by the one-dot-one-dash line, the locus in this
case is within the circle and the occupied space is reduced.
Although the shift timing of the wheeled worktable 1 from the
return passage 14 to the turning part 16 is early since the shift
position S.sub.9 is on the upstream side of the position S.sub.6 in
the case of FIG. 6, which is superior to the case in FIG. 6, the
shift timing from the turning part 16 to the straight outbound
passage 13 is late since the position T.sub.9 is on the downstream
side of the conveyance passage 12 compared with the position
T.sub.6 in FIG. 6, and this delay in the timing so great as leaving
some useless part behind after canceling out the foregoing
advantageous result; this concludes that the extra space is
occupied in this case by comparison with the one in FIG. 6.
[0060] The wheel layout of the one in FIG. 10 is as shown in FIG.
10A, wherein the driving wheel 3m is disposed on the center line L
and at a position 600 mm apart from the center o to the left in the
figure while the two trailing wheels 3s are disposed on an
orthogonal line that crosses the center line L at the center o of
the bottom and 600 mm apart symmetrically on both sides of the
center line L. The locus of the wheeled worktable 1 turning at the
turning part 16 is as shown in FIG. 10B.
[0061] Compared with the locus of the wheeled worktable 1 in FIG.
6, which is shown by the one-dot-one-dash line, the locus in this
case is also within the circle and the occupied space is reduced.
Although the shift position S.sub.10 of the wheeled worktable 1
from the return passage 14 to the turning part 16 is approximately
the same as the position S.sub.6 in the case of FIG. 6, the shift
timing from the turning part 16 to the straight outbound passage 13
is late since the position T.sub.10 is considerably far on the
downstream side of the conveyance passage 12, compared with the
position T.sub.6 in FIG. 6, and this also concludes that the extra
space is occupied in this case in the same way as the in the case
in FIG. 9.
[0062] The other simulation with varied wheel layouts besides the
cases shown in FIGS. 8 through 10 indicate that the turning loci at
the turning part include the useless space, compared with the
embodiment shown in FIG. 6, in the same way as the cases shown in
FIGS. 8 through 10.
[0063] Thus, the wheel layout in this embodiment can minimize the
occupation area of the turning locus of the wheeled worktable 1 at
the turning part 16 (15) and the assembly line with the best space
occupation efficiency as a whole can be constructed.
[0064] Although the wheel layout of the embodiment shows actual
dimensions in FIG. 5 and FIG. 6A, this is described generally with
reference numerals and signs in FIG. 5 as follows: a driving wheel
that has a steering function is disposed at a vertex of an
isosceles triangle Tr that is defined as an isosceles triangle Tr
whose base d1 and height d2 are equal is defined in such manner
that a symmetry axis thereof overlaps the center line L in the
longitudinal direction (travelling direction of the wheeled
worktable 1) and whose base d1 includes a midpoint of the center
line L while trailing wheels are securely disposed at both ends of
the base dl in such manner that the revolving surfaces thereof are
always in a direction parallel to the travelling direction of the
wheeled worktable 1.
[0065] As described above, since the invention wherein each of the
wheeled worktables moving in the assembly line travels
self-dependently with drive of the motor while being isolated from
the others and wherein each of the wheeled worktables is equipped
with the sensor and inducted by the sensor recognition objects that
are installed along the predetermined route on the floor surface
enables modification of the conveyance passage for any increase or
decrease in the wheeled worktables only with replacement of the
sensor recognition objects and thus the conveyance route can be
modified into any desired form by the simple operation without
causing any degradation in the conveyance efficiency at the
increase or decrease in the wheeled worktable number.
[0066] At the wheeled worktable replacement, since each of the
wheeled worktables are isolated from the others and induced along
the conveyance passage only with the sensor inducement system,
being free from any mechanical restraint, there is no need for such
labor and time for dismounting from and remounting on the chain as
in the case of the assembly line driven with the endless chain.
[0067] With use of the wheeled worktable that has the configuration
wherein the rectangle whose center line is parallel to the
travelling direction of the wheeled worktable is defined on the
bottom surface of the wheeled worktable while the isosceles
triangle whose base and height are equal is defined in such manner
that the symmetry axis thereof overlaps the center line of the
rectangle with the base including the midpoint of the rectangle and
wherein the driving wheel that has the steering function is
disposed at the vertex of the isosceles triangle while the trailing
wheels are securely disposed at both ends of the base in such
manner that the revolving surfaces thereof are always in the
direction parallel to the travelling direction of the wheeled
worktable, the turning loci at the turning parts can be minimized
and thus the assembly-line occupation area may be reduced.
* * * * *