Conveyor system utilizing linear motor

A conveyor system comprising a conveyor vehicle, a guide rail for supporting the conveyor vehicle to be freely movable relative thereto, and a linear motor including a primary coil and a secondary conductor for driving the conveyor vehicle. The primary coil is mounted on the conveyor vehicle and the secondary conductor is mounted on the guide rail. The guide rail defines a secondary conductor support portion for limiting downward and transverse movements of the secondary conductor.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a conveyor system utilizing a linear 
motor, and more particularly to a conveyor system comprising a conveyor 
cart having running wheels, a guide rail for movably supporting the 
conveyor cart, and a linear motor a primary coil and a secondary conductor 
for driving the conveyor cart. 
(2) Description of the Prior Art 
This type of conveyor system utilizing a linear motor is characterized by 
its ability to run the conveyor cart at high speed by means of a simple 
construction. This conveyor system utilizes the linear motor to provide a 
propelling force for the high speed running of the cart. For realizing a 
lightweight cart body or where relatively light articles are conveyed, the 
secondary conductor is mounted on the cart and the primary coil on the 
guide rail since this allows a simple cart body construction. Conversely, 
where a great propelling force is required for conveying heavy articles or 
where a high speed conveyance is desired, the primary coil is mounted on 
the cart and the secondary conductor on the guide rail. 
For driving the cart by means of the linear motor, the smaller the space 
between the primary coil and the secondary conductor the greater 
propelling force is generated. The space between the primary coil and the 
secondary conductor is maintained by utilizing the construction wherein 
the conveyor cart is supported through its running wheels by the guide 
rail. FIG. 15 of the accompanying drawings shows an example where primary 
coil C is mounted on the conveyor cart or vehicle V and secondary 
conductor P mounted on the guide rail A. In this case the primary coil C 
and secondary conductor P are fixed to a vertical relative relationship by 
running wheels 1. 
Existing conveyor systems utilizing the linear motor have unsatisfactory 
operability. In a positional relationship as shown in FIG. 15, for 
example, primary coil C or secondary conductor P mounted on the vehicle V 
is disposed over secondary conductor P or primary coil C mounted on the 
guide rail A. The primary coil and the secondary conductor usually are 
spaced from one another by 2 mm or less. However, the running wheels 
inevitably become worn with use of the conveyor system which results in 
reduced diameters of the running wheels and changes in the space between 
the primary coil and the secondary conductor. This would cause the trouble 
of the primary coil and the secondary conductor getting damaged through 
mutual contacts. It is therefore necessary to change the running wheels 
when appropriate. However, the changing of running wheels tends to be 
forgotten since their wear progresses only slowly. The running wheels left 
unchanged lead to the above-noted trouble impeding the working of the 
conveyor system. 
Thus, the known conveyor systems utilizing the linear motor require the 
wear of the running wheels to be kept under observation. In this sense the 
known systems have room for improvement with respect to operability. 
SUMMARY OF THE INVENTION 
Having regard to the drawback of the prior art as noted above, the object 
of the present invention is to provide a conveyor system utilizing the 
linear motor with excellent operability. 
In order to achieve the above object, a conveyor system according to this 
invention has a characterizing feature in that the guide rail supports the 
secondary conductor or primary coil above the primary coil or secondary 
conductor supported by the conveyor vehicle. This construction has the 
following function and effect. 
Since the secondary conductor or primary coil on the guide rail is disposed 
above the primary coil or secondary conductor on the conveyor vehicle, a 
space between the primary coil and secondary conductor is enlarged as a 
result of wear of the running wheels which lowers the vehicle with respect 
to the guide rail. Therefore, even if changing of the running wheels is 
forgotten, the primary coil and secondary conductor will never be damaged 
through mutual contact. The invention is free from such a serious trouble 
as the primary coil and secondary conductor becoming damaged through 
mutual contact. Consequently, the invention provides a conveyor system 
utilizing the linear motor with excellent operability. 
Other advantages of the conveyor system according to the present invention 
will be apparent from the description of preferred embodiments to follow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will be described in detail 
hereinafter with reference to the drawings. 
As shown in FIGS. 1 and 2, a conveyor system utilizing a linear motor 
according to the invention comprises a guide rail A for movably supporting 
a conveyor cart or vehicle V having running wheels 1. The vehicle V is 
driven by a linear motor M to convey articles along the guide rail A. 
The linear motor M comprises primary coil C attached to the vehicle V and a 
secondary conductor P attached to the guide rail A. The primary coil C is 
disposed under the secondary conductor P. 
Details of this construction will be described next with reference to FIGS. 
1 through 3. 
The guide rail A has a substantially C-shaped section and defines a channel 
groove 2 in a lower inside wall thereof for engaging the running wheels 1. 
The guide rail A supports five trolley rails or electric conductor rails 3 
arranged vertically on a lateral inside wall. The conductor rails 3 
consist of three power supply trolley rails 3a and two signal transmitter 
trolley rails 3b. The power supply trolley rails 3a supply power in 
three-phase current from an external power source E to the primary coil C 
and various devices mounted on the vehicle V. The signal transmitter 
trolley rails 3b are for transmitting control signals between a central 
control unit B on the ground and a control unit D mounted on the vehicle 
V. 
The guide rail A includes marks m mounted on an upper end thereof to 
project toward an opening thereof for instructing target running speeds 
.omega. of the vehicle V, as described in detail later. These marks m are 
formed of a magnetic material such as steel. 
For providing the secondary conductor P on the guide rail A, the guide rail 
A is formed of a non-magnetic material such as aluminum and includes a 
bottom face thereof acting as non-magnetic member P1 constituting part of 
the secondary conductor P. The bottom wall of the guide rail A defines two 
right and left hollows 4 extending in parallel longitudinally of the guide 
rail A. Magnetic members P2 formed of a magnetic material such as steel 
are inserted into these hollows 4 from an end or ends of the guide rail A, 
as shown in FIG. 16, and securely supported therein to constitute part of 
the secondary conductor P. Thus, the secondary conductor P has a composite 
construction comprising the non-magnetic member P1 defined on the bottom 
face of the guide rail A itself and the magnetic members P2 inserted into 
the hollows 4 defined in the bottom wall of the guide rail A, thereby to 
provide a strong propelling force. Wedges 5 are driven in at suitable 
lateral positions of the guide rail A to secure the magnetic members P2 to 
the guide rail A while allowing expansion and contraction thereof 
longitudinally of the guide rail A. By securing the magnetic members P2 to 
the guide rail A by means of the wedges 5 acting in transverse directions, 
the difference in longitudinal expansion and contraction due to a 
difference in thermal expansion coefficient between the magnetic members 
P2 and the guide rail A can be absorbed by a relative longitudinal 
movement between the magnetic members P2 and guide rail A. The hollows 4 
constitute a secondary conductor support for preventing or limiting 
downward and transverse movements of the magnetic members P2 constituting 
part of the secondary conductor P. The secondary conductor support formed 
integrally with the guide rail A as described above simplifies a secondary 
conductor mounting operation, and greatly improves the efficiency of 
installation of the conveyor system. 
The secondary conductor support may have various configurations only if the 
downward and transverse movements of the secondary conductor P are 
prevented or limited. As shown in FIG. 4, for example, the guide rail A 
may include projections 4b having L-shape and inverted T-shape sections 
formed integrally with the bottom face thereof, namely the face opposed to 
the primary coil C, these projections 4b being at lateral sides of 
secondary conductors P, respectively. In this case the secondary 
conductors P in band plate form are inserted from a longitudinal end or 
ends of the guide rail A, and the projections 4b act to prevent or limit 
the downward and transverse movements of the secondary conductors P. 
FIG. 5 shows a further example of secondary conductor support structure 
which includes engaging portions 4c and 4d formed integrally with the 
secondary conductor P and the guide rail A, respectively. These engaging 
portions 4c and 4d are in engagement with one another to prevent the 
downward and transverse movements of the secondary conductor P. 
Instead of the composite construction comprising the non-magnetic member P1 
and the magnetic members P2 such as of steel placed one over the other to 
provide a strong propulsive force, the secondary conductor P may be formed 
only of a non-magnetic material such as aluminum or of a non-magnetic 
material. The guide rail A itself may comprise a non-magnetic material or 
a magnetic material formed into a desired shape by injection molding, 
extrusion molding or press shaping. The guide rail A may be formed of a 
non-metallic material, with the secondary conductor support comprising 
hollows 4 for receiving the secondary conductor P or engaging portions for 
retaining the secondary conductor P. Further, for the secondary conductor 
P to be supported by the guide rail A, the secondary conductor P may just 
be press fit to the secondary conductor support formed integrally with the 
guide rail A. 
Although transverse expansion and contraction of the guide rail A and the 
magnetic members P2 occur only to a limited extent and are therefore 
negligible, the hollows 4 may be formed slightly wider than the magnetic 
members P2 mounted therein for absorbing the expansion and contraction. 
The conveyor vehicle V comprises main frames 6 provided at a front end and 
a rear end thereof, respectively, each main frame having a substantially 
L-shaped configuration when viewed from the vehicle front, and a 
connecting frame 6A interconnecting lower ends of the main frames 6. The 
vehicle V further comprises a carrier 7 disposed below the vehicle body 
for supporting the articles. The carrier 7 includes as its main components 
a front and a rear pipe members bent into a substantially C-shaped 
configuration. 
The primary coil C is mounted above the connecting frame 6A, and space 
setting rollers 8 are provided below the running wheels 1. Therefore, even 
when an attraction is generated between the secondary conductor P and the 
primary coil C, the primary coil C never contacts the guide rail A. In 
other words, the rollers 8 contact an outer bottom surface of the guide 
rail A as the vehicle V moves up and down, to prevent the primary coil C 
from approaching the secondary conductor P within a predetermined distance 
thereto. With this construction, therefore, no trouble will result from 
minor errors occurring when the primary coil C is assembled into the 
conveyor vehicle V or when the secondary conductor P is assembled into the 
guide rail A. 
The running wheels 1 are mounted adjacent top ends of the main frames 6 
which act as support frames. A pair of right and left guide rollers 10 is 
provided at the top end of each main frame 6 and in front of and behind 
each running wheel 1. The guide rollers 10 contact right and left sides of 
ridges 9 defined at upper and lower ends of the inside wall of the guide 
rail A, to prevent the vehicle V from running off the guide rail A. 
Number 11 in FIG. 1 indicates a collector unit opposed to the trolley rails 
3 mounted on the lateral inside wall of the guide rail A. The collector 
unit 11 is attached to a bracket 34 extending from one of the main frames 
6. Number 32 indicates a magnetism-responsive proximity sensor for 
detecting the marks m for instructing target running speeds. The sensor 32 
outputs a mark detection signal S1 which becomes high level during a mark 
detection time and low level during a non-detection time. 
One of the running wheels 1 is provided with an electromagnetic running 
brake 12 which is operable when not electrified and inoperable when 
electrified. The other running wheel 1 is provided with a rotary encoder 
13 acting as rotation detecting sensor for detecting a rotational speed of 
this running wheel 1, namely a running speed and a running distance. This 
rotary encoder may be replaced, for example, by a tachogenerator. 
The conveyor vehicle V runs while information is exchanged via the two 
signal transmitting trolley rails 3b between the central control unit B 
and the control unit D mounted on the vehicle V. The running distance and 
speed of the vehicle V relative to the guide rail A are calculated on the 
basis of information provided by the rotary encoder 13. Thus, the vehicle 
V is locatable at all times. In other words, the position of vehicle V is 
known through the central control unit B on the ground. By controlling 
electrification of the primary coil C and the electromagnetic brake 12, 
the conveyor system starts the vehicle V from a fixed position, and 
accelerates, decelerates and stops the vehicle V all automatically. Under 
these controls the vehicle V runs continuously and in a stable manner at 
instructed speeds. Besides, the vehicle V can be stopped at a selected 
position by correcting errors as to the stopping position. 
For controlling the electrification of the primary coil C, the foregoing 
embodiment employs a voltage control mode wherein the voltage applied to 
the primary coil C is varied to adjust the acceleration, deceleration and 
running speed of the vehicle V. 
FIG. 6 is an enlarged view of the electromagnetic brake 12 for braking the 
vehicle V. This brake 12 is the disk type comprising a rotor 16 rotatable 
with an axle 1a, and an armature 18 supported by a brake casing 17 to be 
movable axially of the axle 1a. The armature 18 is biased by springs 19 to 
return to a braking position, and is movable by an electromagnetic coil 20 
against the biasing force of springs 19. 
The brake casing 17 comprises an inner case portion 17A attached to the 
vehicle V acting also as a flange, and an outer case portion 17B acting 
also as stator. The two case portions 17A and 17B are interconnected by 
bolts 21 extending through the outer case portion 17B and screwed into the 
inner case portion 17A. The two case portions 17A and 17B are biased away 
from one another by springs 22 fitted on the bolts 21. Thus, a space 
between the armature 18 and the outer case portion 17B is adjustable by 
turning the bolts 21. Number 23 in FIG. 6 indicates a dust cover extending 
between the two case portions 17A and 17B. Number 24 indicates an adjuster 
ring screwed onto the outer case portion 17B for adjusting the force of 
the springs 22 for biasing the armature 18. Number 1A indicates an 
antislipping rubber ring mounted peripherally of the running wheel 1. 
A running control mode will be described next with reference to FIG. 7 
showing a case where the guide rail A defines a running track in loop 
form. The running track includes a vehicle starting point a, curve 
starting points b, curve ending points c, and a point d short of the 
vehicle starting point a. Each of these points a-d is provided with the 
target speed instructing mark m having a length L corresponding to a 
target vehicle speed .omega. for each section of the running track. The 
primary coil C of the linear motor M is electrified under control 
according to information provided by a mark length detector G to be 
described later. The vehicle V is controlled to start from the vehicle 
starting point a, make a circle along the guide rail A and stop at the 
vehicle starting point a. During the run the vehicle speed is 
automatically changed to high speed at straight running sections and to 
low speed at curved sections. Simultaneously therewith, the central 
control unit B is in communication with the control unit D on the vehicle 
V through the signal transmitting trolley rails 3b to automatically start 
and stop the vehicle V. 
The mark length detector G and speed control means operable in response to 
the information provided by the detector G will be particularly described 
hereinafter. The speed control means controls the running speed of the 
conveyor vehicle V, namely the electrification of the primary coil C of 
linear motor M. 
As shown in FIG. 8, the mark length detector G includes a counter 33 for 
counting a pulse signal S0 output from the rotary encoder 13 only during 
the time at which the mark detection signal S1 output from the proximity 
sensor 32 is in high level. The length L of each mark m, namely the target 
running speed .omega., is accurately detected on the basis of a count n of 
the counter 33 regardless of variations in the running speed of vehicle V. 
The speed control means comprises a CPU 14 for calculating the target speed 
.omega., and a speed controller 15 for controlling the running speed of 
the vehicle V. The CPU 14 calculates the target speed .omega. such that 
the greater the count n of the counter 33 or the detected length L the 
higher the target speed .omega. becomes. The speed controller 15 is 
operable in accordance with the target speed .omega. calculated by the CPU 
14 to control the running speed of the vehicle V by means of phase angle 
of the voltage v applied to the primary coil C. Thus, the counter 33, CPU 
14 and speed controller 15 consititute the control unit D. 
How the control unit D operates will be described next. 
When a start command from the central control unit B is input to the CPU 14 
through the signal transmitting trolley rails 3b, the CPU 14 releases the 
electromagnetic brake 12 and supplies the primary coil C with a voltage v 
corresponding to a predetermined initial speed thereby to start the 
vehicle V. 
From then on, acceleration and deceleration are repeated in accordance with 
the lengths of marks m disposed at the points b-d until the mark m 
disposed at the vehicle starting point a for showing a stopping position. 
The repeated speed variations are effected by the speed controller 15 
which controls the voltage v applied to the primary coil C to provide the 
higher running speed the greater the detected length L is. In other words, 
the vehicle V is controlled to run at the target speed .omega. set for 
each of the sections between the points b, c and d. In order to stop the 
vehicle V upon detecting the mark m at the vehicle starting point a, the 
control is arranged to reduce the target speed .omega. to zero in response 
to any length not exceeding the length of this mark m. 
When the vehicle V completes a circle run along the guide rail A and 
reaches the starting point a, the power for the electromagnetic brake 12 
is cut off to automatically stop and retain the vehicle V at the starting 
point a. For effecting an emergency stop, the central control unit B 
outputs an emergency stop command which cuts off the power for the primary 
coil C, whereby the vehicle V is automatically stopped. 
The described running control system employs the marks m disposed at the 
upper end of the guide rail A for instructing the target speeds .omega., 
but such marks m are not absolutely necessary. That is, the central 
control unit B may be adapted to instruct the vehicle V to start, 
accelerate, decelerate and stop at appropriate times in response to 
signals received from the rotary encoder 13 indicating running distances. 
The running brake 12 may comprise a drum type or other types of brake 
instead of the disk type. Further, the brake may be operable with fluid 
pressure instead of electromagnetic force although the latter is 
preferable with a view to lightening and simplifying the vehicle V. Since 
in the foregoing embodiment the electromagnetic brake 12 is mounted on the 
vehicle V, the guide rail A need not have a complicated construction for 
stopping the vehicle V. This permits the entire conveyor system to have a 
simple construction and the vehicle V to be braked reliably at any 
position as necessary. Therefore, the vehicle V may be stopped properly at 
times of emergency also. 
Since the running brake 12 is biased to the operative position when not 
electrified, the vehicle V may be stopped automatically at times of power 
failure or in other abnormal situations. This arrangement is advantageous 
from the safety point of view. Furthermore, the vehicle V running at high 
speed may be stopped at a selected position with high precision. It 
nevertheless will not present any problem if the running brake is biased 
to the inoperative position instead. 
FIG. 9 shows a spur gear reduction mechanism N for permitting the running 
brake to comprise a small brake 42 providing a small braking force. This 
reduction mechanism N includes a large gear 25 rotatable with the axle 1a, 
a small gear 26 and a large gear 27 provided on a relay shaft 29, and a 
small gear 27A connected to the brake 42. Instead of this construction, 
the reduction mechanism N may comprise various other types such as the 
worm gear type, hypoid gear type, cycloid gear type, planetary gear type 
and harmonic type. 
A conductor structure of the vehicle V employed in the conveyor system of 
this invention will be described next. 
FIG. 10 is an enlarged sectional view of one of the conductor rails 1 which 
comprises a main rail body 31 formed of a conductive material such as 
copper and a holder 30 formed of a nonconductive material such as 
synthetic resin. The holder 30 includes a pair of protective walls 30A 
projecting from opposite sides of the main rail body 31 toward collectors 
28 described hereinafter. Number 35 in FIG. 10 indicates collector holders 
for supporting the collectors 28. 
As shown in FIGS. 11 and 12, the collector unit 11 includes a pair of 
collectors 28 for each conductor rail 3. The collectors 28 constituting 
the pair for one conductor rail 3 are spaced from one another 
longitudinally of the vehicle V. The collectors 28 are supported through a 
collector support frame 36 by the vehicle V. The support frame 36 has a 
center portion thereof longitudinally of the vehicle V supported to be 
rotatable on an axis X extending parallel to the direction of projection 
of the protective walls 30A. The support frame 36 comprises a base frame 
36A rotatably attached by a pivot pin 37 to the bracket 34 on the vehicle 
V, a pair of slide shafts 38 slidably extending through the base frame 
36A, an intermediate frame 39 attached to the slide shafts 38, springs 40 
for biasing the slide shafts 38 to mid-positions in their sliding 
direction, the collector holders 35, and a pair of links 41 connecting 
each of the collector holders 35 to the intermediate frame 39 to be 
movable parallel to the direction of projection of the protective walls 
30A. Further, coil springs 43 are provided to act on the links 41 to bias 
the collector holders 35 toward the conductor rail 3. 
The intermediate frame 39 is mounted on the pair of slide shafts 38. Each 
slide shaft 38 is penetrated at upper and lower ends thereof by pins 44. 
These pins 44 act, through washers 45, to receive and retain the 
intermediate frame 39 in position on the slide shafts 38. The intermediate 
frame 39 includes, at each of its forward and rearward ends, link supports 
39A formed in five vertical levels, and link pivoting pins 46 extend 
through these five link supports 39A. 
Thus, the pair of collectors 28 opposed to one conductor rail 3 is 
oscillatable in seesaw movements transversely of the conductor rail 3 
(that is vertically in FIG. 12). A contact pressure acting on the 
protective walls 30A is mitigated by causing both of the collectors 28 to 
contact the protective walls 30A. When the vehicle V moves vertically 
relative to the guide rail A due to vibrations, the intermediate frame 39 
of the support frame 36 moves transversely of the conductor rails 3, 
namely vertically, thereby preventing the collectors 28 from colliding 
hard with the protective walls 30A. Each of the collectors 28 includes a 
cutout groove K at a mid-position in the fore and aft direction for 
cleaning and other purposes. 
The support frame 36 may have various specific constructions other than the 
construction described above. It will serve the purpose if the support 
frame 36 is rotatable on the axis X extending parallel to the direction of 
projection of the protective walls 30A. 
In the foregoing embodiment, all of the collectors in five levels opposed 
to the five conductor rails are oscillatable in unison. However, each pair 
of collectors opposed to one conductor rail may be supported by an 
individual support frame, and five such support frames may be adapted 
rotatable independently of one another. 
The sectional construction of conductor rail 3 may be modified as shown in 
FIGS. 13 and 14. In FIG. 10 the conductor rail 3 defines a flat surface 
for contacting the collectors 28. The examples shown in FIGS. 13 and 14 
comprise conductor rails 3 defining an angled surface T and a curved 
surface T, respectively. The conductor rail 3 with such a surface T has 
the advantage of avoiding damage to the protective walls 30A and 
generation of abrasion powder caused by the collectors 28 contacting the 
upper and lower protective walls 30A which results from vertical movements 
of the collectors 28 incidental to the running of vehicle V. The 
contacting surface T of conductor rail 3 as shown in FIGS. 13 and 14 may 
be varied in sectional shape in many ways. It will serve the purpose if 
the contacting surface T is recessed progressively deeper toward the 
center transversely of the conductor rail. 
The present invention may be embodied with the secondary conductor P 
mounted on the conveyor vehicle V and the primary coil mounted on the 
guide rail A. In this case, the primary coil C may be provided throughout 
the entire length of the guide rail A, or may be arranged at fixed 
intervals wherein the vehicle is allowed to run by inertia between two 
adjacent primary coils. 
The present invention of course is applicable also to the construction 
where the conveyor vehicle V runs along the upper face of the guide rail. 
In any case it is in accordance with the present invention if the primary 
coil or secondary conductor mounted on the vehicle V is below the 
secondary conductor or primary coil or coils mounted on the guide rail A 
such that the primary coil and the secondary conductor will not approach 
one another with wear of the running wheels.