Conveyors: power-driven – Conveyor section – Endless conveyor
Reexamination Certificate
2000-08-25
2002-03-05
Ellis, Christopher P. (Department: 2632)
Conveyors: power-driven
Conveyor section
Endless conveyor
Reexamination Certificate
active
06352149
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to conveyor belts having electrical conductors, which are sensor loops embedded therein, and more particularly to belts having signal inverting type sensor loops.
BACKGROUND OF THE INVENTION
It is known to transport bulk materials, such as metallic ore and the like, with a heavy duty conveyor belt. These belts may be on the order of miles (1 mile=1.6 kilometers) long. Sharp edges of the material being transported may become lodged in such a position in the conveyor belt mechanism that they can cause a rip (slit, cut or tear) in the belt. When such a rip or tear commences, if the belt is not stopped, the rip can propagate longitudinally for a substantial distance along the belt. Ripped or torn portions of the belt must then be repaired. The costs can be quite formidable for repairing such heavy duty conveyor belts, as well as the cost of cleaning up material which has spilled off of the conveyor belt. It is therefore generally well known to detect and locate a rip in the belt as quickly as possible after it commences, thereby minimizing the extent of the damage to the belt.
It is therefore known to employ sensors within the conveyor belts as part of a rip detection system. These sensors may take the form of loops of conductive wire, and operate in conjunction with an overall rip detection system. Generally, the rip detection system functions by ‘inferentially’ determining whether a sensor (sensor loop) has been damaged, i.e., is an open circuit rather than a closed circuit, as a result of a rip or tear in the belt. Typically an electrical energy source external to the belt is inductively or capacitively coupled to a sensor in the belt. For example, a transmitter/receiver (exciter/detector) external to the belt and which is inductively or capacitively coupled to the sensor is used to detect a break in the conductive wire loop of the sensor. A plurality of such sensors may be disposed at a corresponding plurality of intervals along the length of the conveyor belt. Also, a plurality of exciter/detectors may be disposed at various locations adjacent the length of the belt. In this manner, the damage from rips or tears can be minimized.
U.S. Pat. No. 3,742,477 (Enabnit; 1973) discloses a conveyor belt condition monitoring apparatus for monitoring the open-circuited or close-circuited condition of electrical conductors associated with the conveyor belt. The electrical conductors comprise sensor loops, and are embedded in the conveyor belt. Generally, the monitoring apparatus comprises a detector circuit including an oscillator disposed so as to detect the proximate passage of a close-circuited (i.e., undamaged) sensor loop. The sensor loops disclosed in this patent each employ a single wire which passes (crosses) over (or under) itself in at least two places in order to form a pair of inverted coils. As a general proposition, an elongate element (e.g., a conductor), which is used to form a pair of inverted coils can be described as a “figure-eight sensor loop” will have at least one “crossover”.
U.S. Pat. No. 4,621,727 (Strader; 1986) discloses a conveyor belt damage sensor in which conductors freely move during flexing of the belt by enclosing the conductors in low coefficient of friction jacketing envelopes. As illustrated in
FIG. 5
of this patent, a (sensor) conductor is disclosed which comprises a coiled conductor (
62
) surrounded by an extruded thermoplastic resin envelope (
60
). Multiple formations of figure-eight sensor loops are disclosed wherein the conductor contained within its envelope passes (crosses) over/under itself multiple times.
U.S. Pat. No. 4,854,446 (Strader; 1989;“'446 Patent”) discloses electrical conductors formed into a “figure-eight” pattern embedded in a conveyor belt. The electrical conductors of the sensor loops may be “wavy”, in the form of a repeating flat sinusoidal wave form, to accommodate flexure of the belt without losing continuity (close-circuitness). A typical conveyor belt construction is shown in
FIG. 6
of the patent. The belt (
90
) has a top layer (
92
) which has an outer load carrying surface or “cover”, and a bottom layer (
94
) which has an outer pulley engaging surface or cover. The bottom layer is sometimes referred to as a “pulley cover”. Reinforcing cables (
98
) are disposed between the top and bottom layers. Each of the top and bottom layers has a layer (
100
) of insulation gum on an inner surface thereof, for engaging with each other and with the cables (
98
). The electrical conductors (sensor loops) (
108
) are shown as being disposed between the bottom layer (
94
) and the cables (
98
), with an insulation layer (
104
) and an optional fabric layer (
106
) lying between the conductors (
108
) and the cables (
98
).
FIG. 1
, comparable to
FIG. 1
of the '446 patent, illustrates the prior art rip detection system as set forth in the '446 patent to Strader. A belt rip detection system is shown generally by reference numeral
100
. An elastomeric conveyor belt
104
is driven around/over rollers or pulleys
102
and
103
. A motor
110
provides the power to drive roller
103
which in turn drives the conveyor belt
104
in a direction of travel as indicated by arrow
111
. Of course, the motor could also drive the belt in the opposite direction.
A plurality of conductors
105
(sensor loops or sensors) are embedded in the elastomeric belt
104
transverse to the direction of travel. The conductors
105
are arranged generally in a signal inverting format.
The conductors/sensors
105
may be used in connection with a rip detection system which may use either magnetic or electric fields for excitation/detection. The conductors
105
carry a current flow therein when subjected to an electrical or magnetic field. A rip in the belt
104
will eventually propagate far enough to cause one of the conductors
105
to be broken. A transmitter
106
emits an electrical or magnetic field which is communicated by conductors
105
to a receiver
107
provided that the conductor
105
is intact. Receiver
107
provides a signal to control circuitry
101
which can process the signal and indicate a rip. The rip signal may result in an alarm and/or a signal
108
to the motor controller
109
to automatically stop motor
110
and shut down the conveyor belt
104
.
The electrical conductors
105
are embedded within a conveyor belt
104
which comprises an elastomeric body having a load carrying surface (cover) and a parallel pulley engaging cover with a reinforcement ply disposed within the elastomeric body. The electrical conductors
105
can be embedded into either the load carrying or the pulley engaging surfaces, located between reinforcing plies, or between a reinforcing ply and either load carrying or pulley engaging surface. The electrical conductors can be located either longitudinally or transversely with respect to the belt. The electrical conductors are arranged in a pattern such as a loop, oval, polygon, or in substantially a figure-eight.
FIG. 2
, comparable to
FIG. 6
in the '446 patent, illustrates the installation of a conductor in the prior art belt construction. Reference numeral
200
denotes a conveyor belt. Load bearing surface
202
is secured to reinforcing cables
204
by gum
203
. Conductor assembly
205
is comprised of insulation
206
, fabric
207
and wire
208
. Tie gum
209
secures the conductor assembly
205
to the cables
204
and to a bottom pulley cover
210
. Compactor
201
compresses the assembly together prior to the belt being fed to a press and finally vulcanized.
FIG. 3
illustrates the crossover of the insulated coated fabric and wire of the conductor caused by forming the figure eight sensor loop configuration as disclosed in the '446 patent. The total thickness of the crossover of insulated fabric
207
and wire portions
301
and
302
of a sensor loop
105
conductor assembly
205
is represented by reference numeral
303
and is twice the diameter of the wire plus the thickness of the fabric.
Although
Cohn Howard M.
Deuble Mark A.
Ellis Christopher P.
The Goodyear Tire & Rubber Company
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