Abstract:
A gyro-stabilized automatic pet door is installed in a hinged door and is actuated by a magnet worn by a pet. The automatic pet door prevents unintended openings caused by the Earth&#39;s ambient magnetic field that may trigger a magnetic detector that responds to the magnet worn by the pet. A microelectromechanical systems gyro disposed on the hinged door generates a signal in response to a movement of the hinged door that engages a lockout timer overriding the signal from the magnetic detector and preventing the pet door from opening.

Description:
FIELD OF THE INVENTION 
     The present invention pertains to a gyro-stabilized automatic pet door actuated by a magnet worn by a pet that prevents unintended openings caused by the Earth&#39;s ambient magnetic field. 
     BACKGROUND OF THE INVENTION 
     Automatic pet doors actuated by a magnet worn by a pet have numerous advantages over other types of automatic pet doors. These advantages include preventing unauthorized pets from opening the pet door, allowing the authorized pets to open the pet door without having to force it open, being relatively secure against burglars, reliably weatherproof and inexpensive to provide and install. 
     However, automatic pet doors actuated by a magnet worn by a pet of the prior art have a disadvantage, namely, they may react to the Earth&#39;s ambient magnetic field rather than the magnet worn by a pet, causing unintended openings. Such unintended openings happen most frequently in the automatic pet doors installed in hinged entrance doors to a residence. When a pet owner opens the entrance door, the magnetic detector adapted to react to the specific rate of motion of the magnet worn by the pet moves in an ark through the Earth&#39;s magnetic field. The magnetic detector frequently cannot distinguish between the motion of the magnet worn by the pet and the motion of the door, thus causing the pet door to open. This causes annoyance to pet owners and is undesirable. 
     Unintended openings may also be caused by rattling of the entrance door due to a storm, earthquake and the like, or even by a pet that is not allowed to go out scratching and attacking the pet door. Another undesirable situation is when the pet owner and the pet wearing a magnet reach an entrance door together, the pet door may open at the same time as the entrance door and the pet owner may accidentally drag the pet that is half way through the pet door. 
     Therefore, there is a need for an automatic pet door actuated by a magnet worn by a pet that prevents unintended openings caused by the Earth&#39;s ambient magnetic field. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies this need. It comprises a microelectromechanical systems gyro (also known as and referred to in this Specification as the “MEMS gyro”) disposed on the hinged door that generates a signal in response to a movement of the hinged door that overrides the signal from the magnetic detector and prevents the pet door from opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         FIG. 1  shows an automatic pet door according to the preferred embodiment of this invention with the pet door in the closed position. 
         FIG. 2  shows an automatic pet door according to the preferred embodiment of this invention with the pet door in the open position. 
         FIG. 3  shows a magnetic transmitter worn by a pet. 
         FIG. 4  shows a block diagram of a control means. 
         FIG. 5  shows a locking means. 
         FIG. 6  shows an isometric view of an automatic pet door according to the preferred embodiment of this invention with the pet door in the closed position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     This invention will be better understood with the reference to  FIG. 1  through  FIG. 6 . The same numerals indicate the same elements in all drawing figures. 
     Viewing, simultaneously,  FIG. 1  and  FIG. 2 , numeral  10  indicates a frame. Frame  10  is of a substantially rectangular shape and is disposed over an opening in a hinged door indicated by numeral  70  in  FIG. 2 . The hinged door itself is not shown in  FIG. 1  and  FIG. 2 . A lower portion of frame  10  defines a passage through opening  70  used by pets to pass through opening  70 . 
     Numeral  30  indicates a pet door. Pet door  30  is movable between a lower closed position shown in  FIG. 1  and an upper open position shown in  FIG. 2 . by a drive means. In the preferred embodiment shown in  FIG. 1  and  FIG. 2 , frame  70  comprises two substantially parallel vertical columns indicated by numeral  20 . Columns  20  have channels disposed along their length, such that openings of the channels are facing each other and slidably receive pet door  30 . Further, in the preferred embodiment shown in  FIG. 1  and  FIG. 2 , the drive means comprises a motor indicated by numeral  40 . Motor  40  is disposed on frame  70 . Numeral  50  indicates a primary pulley. Primary pulley  50  is disposed on motor  40 . 
     Numeral  60  indicates a cable. Cable  60  has a first end indicated by numeral  60   a  and a second end indicated by numeral  60   b . First end  60   a  is fixedly attached to primary pulley  50  and second end  60   b  is fixedly attached to pet door  30 . 
     When motor  40  is energized, it spins primary pulley  50 , thereby causing cable  60  to pull pet door  30  to the open position shown in  FIG. 2 . When motor  40  is not energized, pet door  30  is allowed to move down to the closed position shown in  FIG. 1  by way of the force of gravity. In the preferred embodiment described in reference to  FIG. 1  and  FIG. 2 , there is also a clutch allowing primary pulley  50  to slip while motor  40  is energized and pet door  30  is in the open position. 
     In the preferred embodiment, there is also a secondary pulley indicated by numeral  170  and a pivot pin indicated by numeral  180 . Secondary pulley  170  is disposed on frame  70 . Pivot pin  180  is disposed on pet door  30 . Cable  60  rises at a substantially 30 degree angle from horizontal from primary pulley  50  to secondary pulley  170  and then descends at a substantially 90 degree angle from horizontal to pivot pin  180  and then leads, substantially horizontally, from pivot pin  180  to proximal end  60   b.    
     Viewing now  FIG. 3 , numeral  80  indicates a magnetic transmitter. Magnetic transmitter  80  is worn by a pet. Magnetic transmitter  80  generates a predetermined transmitter signal. There provided a detector located proximate frame  70  (not shown in  FIG. 1  and  FIG. 2 ) generating a detector signal in response to the transmitter signal when the pet wearing transmitter  80  approaches pet door at a predetermined distance from pet door  30 . In the preferred embodiment, the predetermined distance ranges from about six inches to about four feet and can be adjusted by the pet owner, depending on the size of the pet. 
     Viewing now  FIG. 4 , numeral  100  indicates a control means. Control means  100  engages the drive means (namely motor  40  in the preferred embodiment) to lift pet door  30  between the closed and open positions in response to the detector signal. Numeral  90  indicates a detector (as discussed above, detector  90  is located proximate to frame  10 ). Detector  90  has a relatively large inductance (i.e. many turns of wire), which permits it to generate a small DC voltage due to transmitter  80  moving about detector  90 . When transmitter  80  is father away from detector  90  than the predetermined distance, the voltage induced in detector  90  is negligibly low. 
     Numeral  110  indicates a MEMS gyro. MEMS gyro  110  is disposed on the hinged door and generates a gyro signal in response to a movement of the hinged door. The gyro signal overrides the detector signal, thus preventing lifting pet door  30  between the closed and open positions. In the preferred embodiment, MEMS gyro  110  is a motion detector, even though an accelerometer MEMS gyro can be used. A motion detector gyro is preferred due its ability to sense angular notion and not just vibrations. In the preferred embodiment, the gyro signal is generated from MEMS gyro  100  X-axis sensor. However, the Y-axis sensor or axis sensor can be used, depending on the orientation of MEMS gyro  110  on the hinged door. 
     Numeral  120  indicates a lockout timer. Lockout timer  120  prevents lifting pet door  30  between the closed and open positions during a lockout period following substantially immediately after pet door  30  returns to the closed position. The purpose of lockout timer  120  is to prevent pet door  30  from opening and closing for a period of time in the event the pet is loitering near pet door  30  and causing control means  100  to engage motor  40 . In the preferred embodiment, the lockout period ranges from about ten seconds to about thirty seconds. It can be adjusted by the pet owner, based on the habits of the pet. 
     Numeral  130  indicates an open door timer. Open door timer  130  maintains motor  40  energized for a predetermined period of time substantially immediately following energizing in response to the detector signal. The purpose of open door timer  130  is to allow the pet to clear opening  70  without scarring the pet by a suddenly closing pet door  30 . In the preferred embodiment, the predetermined period of time ranges from about one second to about ten seconds. It can be adjusted by the pet owner, based on the habits of the pet. 
     Numeral  140  indicates a first amplifier. First amplifier  140  is a three-stage low frequency amplifier. In the preferred embodiment, first amplifier  140  is tuned to the frequency of about 1 Hz. Through experiments, it has been determined that the frequency of about 1 Hz is advantageous due to the way the pet wearing transmitter  80  approaches or walks towards pet door  30 . 
     First amplifier  140  has a first amplifier input indicated by numeral  140   a  and a first amplifier output indicated by numeral  140   b . First amplifier output  140   h  is connected, through open door timer  130 , to a power switch indicated by numeral  150 . Power switch  150  can be placed in an “on” position and in an “off” position. When power switch  150  is in the “on” position, motor  40  is energized. In the preferred embodiment, power switch  150  is an electronic switch, such as a power Triac, turned in the “on” position by a logic “1” level and turned in the “off” position by a logic. “0”. 
     The detector signal applied by detector  90  to first amplifier input  140   a  causes first amplifier  140  to output a detector signal pulse at first amplifier output  140   b . Said detector signal pulse causes power switch  150  to be placed in the “on” position during the predetermined period (which is, as discussed above, ranges from about one second to about ten seconds). 
     Numeral  160  indicates a second amplifier. Second amplifier  160  is also a three-stage low frequency amplifier. Second amplifier  160  has a second amplifier input indicated by numeral  160   a  and a second amplifier output indicated by numeral  160   b . Second amplifier input  160   a  is connected to MEMS gyro  110 . Second amplifier output  160   b  is connected to lockout timer  120 . Lockout timer  120  is connected, through open door timer  130 , to power switch  150 . 
     The gyro signal applied to second amplifier input  160   a  causes second amplifier  160  to output a gyro signal pulse at second amplifier output  160   b . Said gyro signal pulse causes lockout timer  120  to engage, thus placing power switch  150  in the “off” position and preventing lifting pet door  30  between the closed and open positions. 
     If the detector signal and the gyro signal occur simultaneously (i.e. when the pet approaches pet door  30  and the pet owner starts opening the hinged door at the same time), the gyro signal pulse occurs slightly before the detector signal pulse. This engages lockout timer  120  before open door timer  130  has the opportunity to be engaged by the detector signal pulse and keeps pet door  30  from being lifted between the closed and open positions. 
       FIG. 4  also shows an AND-gate to which first amplifier output  140   b  and lockout timer  120  are connected on one side and open door timer  130  on the other side. Absent the gyro signal pulse, the detector signal pulse engages, simultaneously via the AND-gate, open door timer  130  and lockout timer  120 . This places power switch  150  in the “on” position for the predetermined period, after which the power switch is placed in the “off” position, motor  40  is de-energized and pet door  30  is returned in the closed position. After that, lockout timer  120  that had been engaged by the detector signal pulse keeps power switch  150  in the “off” position during the lockout period after pet door  30  is returned in the closed position. After the lockout period, lockout timer  120  allows open door timer  130  to be re-engaged for another cycle of opening pet door  30 . 
       FIG. 4  also shows an OR-gate comprising a pair of diodes connected to first amplifier output  140   b  and second amplifier output  160   b  on one side and to lockout timer  120  on the other side. First amplifier  140  is made to respond to the detector signal slightly slower than second amplifier  160  responding to the gyro signal. Thus, the gyro signal pulse occurs slightly before the detector signal pulse, even if the detector signal and the gyro signal occur simultaneously. Accordingly, pet door  30  is prevented from being lifter in the open position either when the hinged door moves first or when the hinged door movement and the detector signal occur simultaneously. 
     Viewing now  FIG. 5 , numeral  190  indicates a locking means. Locking means  190  comprises a U-shaped bracket indicated by numeral  200 . U-shaped bracket  200  has flanges indicated by numeral  210  having a pair of holes indicated by numeral  220  therein. 
     Numeral  230  indicates a pin. Pin  230  has a proximate end indicated by numeral  230   a  and a distal end indicated by numeral  2301 . Pin  230  is disposed substantially horizontally within holes  220 , such that proximate end  230   a  and distal end  230   b  project outside flanges  210 . 
     Numeral  240  indicates a compression spring. Compression spring  240  is disposed between flanges  210  and is biasing pin  230  towards distal end  230   b.    
     Numeral  250  indicates a tension spring. Tension spring  250  has one end attached to proximate end  230   a  and the other end attached to second end  60   h  of cable  60 . 
     There is also a pin hole indicated by numeral  260  disposed in column  20 , pin hole  260  receiving and engaging with distal end  230   b  when pet door  30  is lowered in the closed position, thereby preventing lifting pet door  30  by an external force. 
     Viewing now  FIG. 6 , numeral  70   a  indicates the hinged door. MEMS gyro  110  is disposed on hinged door  70   a . Numeral  20   a  indicates the channels. Channels  20   a  are disposed along the length of Columns  20 , such that openings of channels  20   a  are facing each other and slidably receive pet door  30 . Detector  90  is located proximate to frame  10 . Detector  90  is shown in  FIG. 6  as an induction coil having about ten thousand windings. 
     While the present invention has been described and defined by reference to the preferred embodiment of the invention, such reference does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled and knowledgeable in the pertinent arts. The depicted and described preferred embodiment of the invention is exemplary only, and is not exhaustive of the scope of the invention. Consequently, the invention is intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects.