Traditionally, the whereabouts of animals have been controlled by erecting physical barriers such as walls or fences at the site of a boundary the animal is to be prevented from crossing. Such barriers must not only be high enough to prevent the animal from jumping over and dense enough to prevent the animal from passing through any gaps but also substantial enough to withstand attempts by the animal to breach the barrier by physical force. The latter requirement is a serious limitation in that in addition to requiring considerable time and labor to erect, substantial physical barriers are often impracticable due to shortage of materials suitable for their construction.
Those limitations have been overcome to some extent by the development of avoidance-inducing physical barriers, of which, barbed wire and high voltage charged fences are well-known examples. Rather than relying solely on physical strength to defeat attempted breaches, animals quickly learn that contact with such barriers is associated with an aversive stimulus such as being shocked or pricked by sharp barbs. They therefore avoid repeated or sustained attempts to breach them. Physical barriers of the avoidance-inducing type have permitted the fencing of large areas with the expenditure of only a fraction of the time, effort and materials requirements which had previously been necessary. However, avoidance-inducing physical barriers also suffer from some important limitations.
First, like all physical barriers, posts and wires or other above-ground structures are required to erect an avoidance-inducing physical barrier. In some applications, such as the confinement of household pets or guard dogs within a property line, these structures can be unsightly and are sometimes forbidden by deed restrictions or local regulations. Like all physical barriers, avoidance-inducing physical barriers are non-selective. A physical barrier sufficient to control the whereabouts of a particular animal also tends to impede the ingress and egress of persons or other animals except at locations where a gate may be provided. Moreover, the animal can traverse the barrier if the gate is inadvertently left open. Electrified or barbed wire fences intended for controlling the whereabouts of animals can also shock or injure persons, especially young children.
Various electronic systems which do not require the erection of above-ground barrier structures and which are selective in their operation are also known. In these systems, selectivity is achieved by equipping only the animal (or animals) whose whereabouts are to be controlled with an electronic unit capable of sensing when the animal moves into predetermined proximity of a defined boundary and then delivering one or more aversive stimuli to deter the animal from traversing the boundary. Such stimuli commonly comprise an electric shock either alone or in combination with an advance audible tone. Until the advent of the present invention, prior art electronic systems for controlling the whereabouts of animals have generally been one of two basic types which may be referred to as the "wire loop" type and the "remote broadcast" type, respectively.
Various wire loop systems for controlling the whereabouts of animals are exemplified by U.S. Pat. No. 3,753,421 to Peck; U.S. Pat. No. 4,136,338 to Antenore; U.S. Pat. No. 4,733,633 to Yarnall, Sr. et al.; U.S. Pat. No. 4,745,882 to Yarnall, Sr. et al.; U.S. Pat. No. 4,766,847 to Venczel et and U.S. Pat. No. 4,967,695 to Giunta. In such systems, one or more continuous wire loops are routed along an arbitrary path to define a boundary. In some cases the wires are run above ground, in others they are buried. A low level electrical current signal is passed through the loop using a controller connected directly to the loop. The controller itself is typically mounted at an indoor location for protection from the elements as well as for access to an A.C. line from which it derives power. This location can be some distance from the desired boundary. In that case, the wire loop is typically twisted over that portion of its run lying between the controller and the closest point on the boundary.
In operation, the untwisted portions of the wire loop emit a relatively weak electrical field which can be sensed by a battery-powered unit affixed to the animal by suitable means such as by attachment to a collar worn by the animal. When the animal approaches the wire, the unit senses the field and initiates the application of at least one aversive stimulus to the animal. Since the currents in any twisted portions of the wires flow in opposing directions, their fields cancel sufficiently that the unit affixed to the animal does not initiate application of an aversive stimulus even when the animal is near by. Thus, by twisting portions of the loop together, a boundary located remotely from the controller and/or one having two or more distinct portions lying physically separated from one another can be formed using a single loop of wire connected to a single controller.
Some prior art animal whereabouts control systems include an animal-carried stimulator device which are responsive to sensed variations in signal strength as indicating the relative distance of the animal from the boundary. In certain of them, the animal's approach to the wire, as indicated by a received signal strength above a predetermined threshold, initiates application of a first and relatively mild aversive stimulus such as generation of a tone which terminates if the animal retreats from the boundary. If on the other hand, the animal moves closer yet toward the loop, a higher threshold of signal strength is exceeded and a stronger aversive stimulus such as an electric shock is administered in order to repel the animal from the boundary as defined by the location of the wire. While wire-loop type systems have been popular, they too suffer from a number of significant problems.
One problem is that interruption of A.C. power or failure of the controller renders the entire system inoperable. The wiring installation requirements for wire-loop type systems are also a disadvantage. As noted above, a continuous length of wire must be run from the controller, around the desired boundary and back to the controller which is usually located at an indoor location remote from any point on the desired boundary. The wire must be installed around or through any intervening walls or other obstacles. Even with special equipment built for the purpose, it is not a trivial task to bury a wire loop encompassing the perimeter of a large property. In order to cross existing sidewalks, driveways, or other concrete or masonry structures, it may also be necessary to cut through the concrete to provide a channel through which the wiring may be passed. Patches formed over such channels can be unsightly and, if not properly installed, can form areas subject to water infiltration and cracking. In the event the wire loop breaks, the break must be located, excavated and repaired. Until such repair is effected, the entire boundary is disabled, not merely the portion of it in the vicinity of the break in the wire. With buried wire loop systems, reconfiguring the size, shape and/or location of the boundary involves excavating the wire loop and reburying it in a new location or abandoning the existing loop and burying a new one.
Due to the need to twist the loop wires together at locations through which the wires must pass but where no boundary is desired, wire loop systems tend to be difficult to install. This is particularly true in cases where one desires to define boundaries having configurations other than a closed perimeter boundary encompassing an area within which an animal is free to roam. Examples include perimeter boundaries including intentional gaps defining passageways and boundaries including several mutually separated small areas or zones from which the animal is to be excluded.
In order to eliminate the need for boundary wiring, remote broadcast systems for controlling the whereabouts of animals have been proposed. Remote broadcast systems are those in which a perimeter boundary is established by broadcasting a signal from a central location toward an intended outer perimeter boundary. The location of the boundary is defined based on the strength of that broadcast signal as sensed by a unit affixed to the animal. For example, U.S. Pat. No. 5,067,441 to Weinstein describes an animal restraining system including a radio frequency transmitter, a transmitting antenna located inside an area in which the animal is to be restrained and a collar unit worn by the animal. A coaxial cable is run between the transmitter unit and the transmitting antenna. When the animal strays from the transmitting antenna a distance sufficient to permit the signal strength received by the collar unit to fall below a predetermined level, a first aversive of stimulus, such as a beeping tone, is generated. If the animal strays further from the antenna by a distance sufficient to cause the signal strength to fall below a second predetermined threshold, a stronger stimulus such as a shock is administered to the animal to deter its departure from the area. A similar system is described in U.S. Pat. No. 4,898,120 to Brose.
A fundamental shortcoming of remote broadcast type systems for controlling animal whereabouts is that the collar unit worn by the animal does not detect proximity of the animal to a structure whose physical location reliably indicates the location of the intended boundary. Instead, such systems rely on measuring signal strength as an indicator of the distance the animal from a transmitting antenna which may be located a considerable distance from the boundary. Consequently, that indication is not always reliable since the strength of the received signal can change due to constructive and destructive interference generated by signal reflections, shadowing by metallic objects and other uncontrollable variations in local reception conditions. Since local reception conditions can fluctuate, the size, shape and location of the boundary locii at which stimuli will be administered can also fluctuate. For example, if the signal path between the transmitting antenna is temporarily altered by an automobile which pulls into one's driveway, the animal may receive a shock even if the animal remains within an intended perimeter boundary.
Remote broadcast systems are also limited with respect to the sizes and shapes of perimeter boundaries they can define. While generally circular boundaries or ones conforming to the radiation pattern of a particular antenna can be implemented, continuous perimeter boundaries encompassing jutting regions or other well defined irregularities would be extremely difficult, if not impossible to establish using a remote broadcast type system. Another limitation of such systems is that because signal strength values are not unique to individual locations within the field of the transmitter, they are not well suited for excluding an animal only from arbitrarily located distinct positions, such as the site of one's prized rose bush for example. While wire loop systems offer greater flexibility as to boundary shape, they are subject to the problems and limitations described above.
Another limitation of prior art systems is that they are only capable of defining boundaries whose positions remain essentially fixed. There is a need for an animal whereabouts control system which, while suitable of defining fixed boundaries, is also capable of defining boundaries which move with a mobile agent such as a child or another animal so that a particular animal such as a dog can be kept separated from child or other animal while otherwise allowing both dog and child complete freedom of movement.
Prior art systems for controlling the whereabouts of animals also deliver stimuli of substantially invariant intensity. While some systems, such as those described in U.S. Pat. No. 4,898,120 to Brose deliver stimuli whose intensity increases as the animal moves closer to the boundary, small or timid animals are nonetheless administered aversive stimuli of substantially the same intensity as larger or more aggressive animals. At least one system, the PET ALERT buried wire system available from Futuretech, Inc. of Columbus, Ohio, is professedly capable of adjusting stimulus intensity by way of a multiple position switch located at the central control unit. However, in situations where the whereabouts of more than one animal are to be controlled rising a single system, such systems lack the capability permitting a user to independently adjust the intensity of the aversive stimulus to be delivered to each individual animal according to its individual temperament and/or physical characteristics.
As noted above, electronic systems for controlling the whereabouts of an animal typically employ a battery-powered unit affixed to the animal for sensing the boundary and administering a desired stimulus. While battery life of several months is presently achievable using state of the art batteries, achieving even longer operation of such system with state of the art batteries or achieving comparable operating life with less expensive batteries is desired.