Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02309863 2000-OS-11
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MAGNETICALLY POWERED CONVEYOR SYSTEM AND METHOD
This application claims priority under 35 USC ~ 119(e) based on
provisional patent application no. 601100,117 filed on September 14, 1998.
FIELD OF THE INVENTION
The present invention is directed to a conveyor system powered by
linear motors, and more specifically, toward a conveyor system wherein
power supplied along any length of the system can be controlled by changing
the size and spacing of the linear motors.
BACKGROUND OF THE INVENTION
A power and free conveyor system includes a moving power chain, a
power track for guiding and enclosing the power chain, and a free track
generally parallel to the power track and spaced apart therefrom. The free
track supports a number of wheeled trolleys which travel therealong which in
turn support carriers for carrying different objects. The trolleys include
assemblies which extend toward the power track and which assemblies are
engaged by protrusions called dogs extending from the power chain toward
the free track to push the trolleys along the free track in a forward
direction.
The assemblies are movable in the direction of the power track so that they
can be engaged and disengaged from the power chain at proper times to
cause the trolleys to move or stop, respectively. These assemblies and their
moving parts tend to wear out and can introduce debris and contamination
into the system as they move and wear as well as generate noise. Likewise,
the moving parts in the trolley wheels wear, require maintenance and
replacement, and can sometimes introduce contamination into the conveyor
system and the objects being transported thereby.
A power chain is generally a rivetless chain comprising numerous links
which require lubrication to minimize wear as the chain bends and the links
rub against one another. A break at any one of the hundreds or thousands of
links in a chain will shut down an entire conveyor system. Chains are also
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prone to jamming. The power chain and trolley assemblies represents a
significant system cost, is difficult and time consuming to replace when worn
out, and along with the lubricators and lubricants needed to maintain the
chain
and trolleys, is also a significant source of contamination of the materials
being transported. In addition, chain links become thinner as they wear and
chains tend to elongate as they age. This causes problems in maintaining a -
proper spacing between the trolleys and synchronizing different chains to
allow transfers between conveyor lines. Therefore, complex take ups must be
employed to remove any excess slack. Furthermore, the power chain is
continuous and must travel in a loop. The free track, however, may only
extend along one portion of the loop. Thus the length of the power chain must
be about double the length of the free track to allow it to return to the
beginning of the conveyor. Furthermore, the power chain must be enclosed in
the power track along its entire length. The return section of power chain and
track therefore add considerably to the cost of a conveyor system even
though the chain does no useful work along this portion of its path. Clearly
it
would be desirable to provide a conveyor system in which the driving force for
the carriers on the free track could be provided by a mechanism other that a
power chain, and wherein the number of moving parts which wear out and
lead to contamination is reduced.
SUMMARY OF THE INVENTION
The present invention addresses these and other problems by using
linear motors, such as linear induction motors (LIM's) or linear synchronous
motors (LSM's) to move conveyor carriers along a supporting track. The
linear motors are arranged in proximity to the supporting track, and push the
carriers from one linear motor toward the next. The linear motors can also be
used to decelerate and stop carriers either alone or in combination with well
known mechanical stops.
Different driving forces may be required along differ portions of a free
track. For example, more force is required to move carriers up an incline and
to move carriers holding heavy objects. The present system can readily
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accommodate such differing power requirements by using more linear motors
of a proper size and length and spacing the motors more closely in areas
where greater power is needed. In downhill sections of track, motors are
used only for deceleration purposes or dispensed with entirely. This contrasts
with prior chain-driven systems where the power chain was present even
along downhill track portions where power was not needed and where-
jamming could occur if a trolley traveling faster than the power chain and
overtook a preceding dog.
In several embodiments of the subject invention, the linear motors are
modular and used together with a motor track having a slot path into which
the motors can be plugged at almost any position. The slot path can also
accommodate motors of various widths and lengths. Power and any
necessary communications connections are provided along the entire length
of the motor track so that a linear motor is ready to operate once it is
plugged
in. When different or additional motors are needed, the linear motors can be
unplugged, rearranged, and returned to the track quickly and easily.
Each of the linear motors is preferably provided with sensors to sense
the approach or presence of a carrier. The system is also provided with a
central controller for monitoring the locations of the carriers as they travel
throughout the system. When a carrier approaches a linear motor, the central
controller will check and authorize the linear motor to move the carrier and
then be energized to push the carrier forward toward the next motor. The
carriers can also be brought to rest by controlling the motors in appropriate
ways or by using mechanical stops as done in the prior art.
In a preferred embodiment, the system includes wheeled trolleys which
travel along a free track. The trolleys are generally similar to standard
trolleys, but instead of an apparatus for engaging a pusher dog on a power
chain, each includes a reaction plate on its top surface. A motor supporting
track positioned parallel to the free track includes a number of LIM's. When a
sensor indicates that a trolley is approaching one of the LIM's the LIM is
actuated to generate a force against the reaction plate and push the trolley
along the track toward the next LIM.
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LIM's are also used in a second embodiment, in this case to power
pusher dogs similar to those which depend from prior art power chains. A
plurality of LIM's are arranged along a power track positioned adjacent to a
free track which supports the trolleys. Each of the trolleys is equipped with
a
projecting portion adapted to be engaged by the pusher dogs on the LIM's.
When a sensor on the LIM detects that a trolley is passing by the LIM, the LIM
is actuated to slide its pusher dog forward, engage the projecting portion of
the trolley and push the trolley toward another LIM. The pusher on the LIM
then returns to its starting position to await the approach of the next
trolley.
Because the L1M's can be controlled by a central controller, the trolleys do
not
require a moving apparatus for disengaging from a power track, thus further
avoiding the use of moving elements which can wear and introduce
contamination into the conveyor system.
In a third embodiment, all moving parts are eliminated and the carriers
are propelled by LSM's. In this embodiment the carriers include magnetic
plates which are both supported and moved in a forward direction by
magnetic fields generated by the support track. By using LSM's built into a
support track, the magnetic plates can be lifted off the support track and
moved forward by the interaction between the magnets on the plates and the
moving magnetic field generated by the LSM by using the retractable portion
of the trolley.
The subject system eliminates the need for a power chain and the
lubrication and maintenance which it requires. Because fewer or no moving
parts are used, maintenance costs are reduced. Complicated drive systems
having chain take-ups to accommodate changes in chain length are
eliminated, and the system is substantially quieter than standard power and
free systems. The subject system is adaptable for both overhead and
inverted power and free systems.
The invention also includes a method of conveying loads using
carriers. The carriers travel on a support track and are driven by a plurality
of
magnetically powered motors, either linear induction motors or linear
synchronous motors. The motor operation is controlled to drive the carriers
for load conveyance.
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It is therefore a primary object of the present invention to provide a
chainless power and free conveyor system;
It is another object of the present invention to provide a power and free
conveyor system in which magnetic force is used to move trolleys and carriers
along a conveyor track;
It is a further object of the present invention to provide a power and,
free conveyor system in which the power provided at any portion of the track
can be varied;
It is still another object of the present invention to provide a power and
free conveyor system powered by modular linear motors which can be
plugged into a power track in a wide variety of arrangements.
It is still a further object of the present invention to provide a conveyor
system having few moving parts.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects will be better understood from a reading and
understanding of the following detailed description of several preferred
embodiments of the invention, together with the following drawings of which:
Figure 1 is a perspective view, partly in section, of a first embodiment
of a conveyor system having a motor track for holding a plurality of linear
motors and a support track for supporting a plurality of trolleys;
Figure 2 is a plan view of the motor track shown in Figure 1 and one of
the linear motors mounted thereon;
Figure 3 is a perspective view of a linear motor and its connectors
suitable for connection to the motor track shown Figure 1;
Figure 4 is an elevational view of a section of conveyor track showing
schematically the spacing of linear motors therealong;
Figure 5 is a second embodiment of a conveyor system including a
plurality of linear motors;
Figure 6 is an elevational view, partly in section, of one of the linear
motors of Figure 5; and,
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Figure 7 is a perspective view of a third embodiment of the subject
invention wherein carriers are levitated and moved along a track by magnetic
force.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawing, wherein the showings are for purposes
of illustrating several preferred embodiments of the subject invention only
and
not for purposes of limiting same, Figure 1 shows a conveyor system 10
having a motor track 12 upon which are mounted a plurality of linear motors
14, and a support track 16 for supporting trolleys 18 and a carrier 20
depending from a pair of the trolley 18. In this embodiment, linear motors 14
are preferably linear induction motors (LIM's). The trolleys 18 each include a
reaction plate 22 formed in the top surface thereof which is separated from
motors 14 by a small distance when the trolleys are properly positioned on
support track 16. As one of the trolleys approaches one of the motors, a
sensor 24 informs a central communication system of the trolley's approach.
If it is safe for the trolley to proceed past the given motor, a signal is
sent to
energize the motor which in turn generates eddy currents in the reaction plate
in a well known manner to push the trolley along the track. The LIM's can
also apply a breaking force to slow the trolleys when necessary; however, it
is
generally advisable to provide conventional mechanical stops (not shown) in
critical portions of the track.
Figure 2 shows one surface of motor track 12 having a large number of
slots 26 arranged in several rows. As seen in Figure 3, each of the linear
motors 14 includes prongs 28 which fit securely within slots 26 to hold the
linear motor in place and to connect the linear motor to power and
communication lines (not shown) inside track 12. This arrangement allows
varying numbers of linear motors to be placed on the track in order to provide
the amount of power needed for a given application. It also makes it easy to
replace motors in the event that one malfunctions.
Figure 4 shows a number of linear motors 14 arranged along a section
of motor track 12 on which carriers will travel from left to right as viewed
in the
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figure. The track includes a first horizontal portion 30, an inclined portion
32,
a second horizontal portion 34, a downhill portion 36 and a third horizontal
portion 38. As will be appreciated from this showing, the linear motors 14 are
spaced apart by a first distance in the horizontal portions 30, 34, and 38,
are
more closely spaced along the inclined portion 32 to provide additional force
for moving carriers up this slope, and are provided only at the bottom section
,
of downhill portion 36 to slow the carriers as they enter third horizontal
portion
38. In this manner, only the necessary amount of power is supplied at any
given section of the system, unlike prior art chain-driven systems where a
constant power level was provided everywhere.
Figure 5 shows a second embodiment of a linear motor driven
conveyor system in which a number of LIM's 40 are supported from the
underside of a motor support track 42. Each of the LIM's 40 includes a
pusher dog 44 adapted to travel between an upstream end 46 and a
downstream end 48 of the LIM. As seen in Figure 6, the pusher dog 44 is
attached to a reaction plate 50 constrained to follow a path 52 within the LIM
housing 54. By property controlling LIM 40 in a well known manner, reaction
plate 50 and pusher dog 44 can be made to travel back and forth between
upstream end 46 and downstream end 48. The system further includes a
plurality of trolleys 56 supported for rolling motion along a free track 58.
Each
trolley includes a protrusion 60 extending in the direction of motor support
track 42. Preferably, these protrusions are fixed with respect to the bodies
of
the trolleys; however they may comprise the movable assemblies that are
found on standard trolleys for engaging and disengaging a power chain.
When used in connection with the subject invention, the movable assemblies
would be fixed in place thus avoiding the problems associated with the use of
moving parts.
Each LIM includes a sensor 62 which is located downstream of end 46
of LIM 40 at a position such that the leading end of a trolley 56 will be
sensed
by the sensor as protrusion 60 passes by pusher dog 44. When the leading
edge of a trolley is sensed, a central controller determines whether the
trolley
should be advanced, and if authorization is obtained, the LIM is actuated to
move pusher dog 44 toward downstream end 48, engaging protrusion 60 and
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pushing trolley 56 forward along the free track. As can be seen in Figures 5
and 6, upstream end 46 of LIM 40 is spaced away from free track 58 a greater
distance than the downstream end 48 to hold pusher dog 44 out of the path of
the trolleys 56 until such time as it is desired to have the pusher dog engage
the trolley.
Figure 7 shows a third embodiment of the subject invention in which
trolleys are eliminated and carriers 64 are moved along a support track 66 by
magnetic levitation. Track 66 comprises a LSM for generating a moving
magnetic field in a well known manner. Each carrier 64 is attached to a
magnetic plate 68 by a support rod 70. When coils 72 generate a magnetic
field having an opposite polarity to that of magnetic plates 68, plates 68 are
repelled from track 66. By controlling the strength and location of the field
produced by coils 72, the carriers can be moved as desired along the track.
The carriers can also be slowed or stopped by controlling the magnetic field
produced by coils 72 in an appropriate manner.
While the drawings show the carriers being supported in an overhead
power and free system, the carriers can be supported from below as in an
inverted power and free system.
The present invention has been described in terms of several preferred
embodiments, however obvious additions and modifications will become
apparent to those skilled in the relevant art upon a reading and understanding
of this application. For example, while the power track is located above the
free track in the preferred embodiments, it could just as easily be located
beneath the free track. These and all other obvious modifications are
intended to be included within the scope of this application.
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