Abstract:
An outlet unit for providing a supply voltage to the prongs of a plug comprising a housing having a plurality of electrically conductive plug channels for receiving the prongs of the plug, a shutter rotatably mounted to the housing and operative in one of a first and a second position, the shutter having openings for receiving the prongs of the plug wherein only when in the second position the openings of the shutter and the plug channels are aligned permitting axial displacement of the prongs into the housing, and a strike plate located between the housing and the shutter for preventing the rotation of the shutter to the second position absent axial displacement of the prongs sufficient to engage the strike plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application relates to and claims priority to United States Provisional Patent Application Ser. No. 60/286,914 entitled “Apparatus for Providing AC Power to Airborne In-Seat Power Systems,” by Hambley et al., that was filed on Apr. 27, 2001. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention relates to an apparatus for converting an input AC signal to an alternatively configured output signal and providing the output signal to one or more devices. More specifically, the present invention relates to a method of producing a modulated AC signal for use by electrical devices as well as an outlet unit through which the AC signal may be channeled. 
     (2) Description of the Related Art 
     There exist outlet units for mating with the prongs of a plug through which power is to be supplied to a device which employ mechanical switches to detect the insertion of a plug. An example of an existing outlet unit is described in U.S. Pat. No. 6,016,016 of Starke et al. the disclosure of which is incorporated herein in its entirety by reference. Some existing outlet units make use of a plug case sensor to determine when it is safe to supply power to a plug. A plug case sensor senses the physical contact of a plug against a surface of the outlet unit. Power is enabled to a device only when the plug of the device exerts sufficient pressure against the plug case sensor to indicate that the plug is sufficiently connected to the outlet unit. Unfortunately, when used on a vehicle, the vibration which often attends the motion of the vehicle is sufficient to dislodge a plug from the plug sensor case. In such circumstances, provision of power to the plug from the outlet unit is rendered intermittent. 
     Many existing outlet units are attached to In Seat Power Systems (ISPS). An example of an ISPS is described in U.S. Pat. No. 5,754,445 of Jouper et al. the disclosure of which is incorporated herein in its entirety by reference. 
     There is therefore needed an outlet unit which can detect a plug insertion without the need for mechanical switches extraneous to the plug itself. In addition, it is preferable to utilize an outlet unit which does not rely upon a plug case sensor to determine when there is sufficient contact between the plug and the outlet unit to continue to provide power. Lastly, there is needed an ISPS configured to filter out the Electro-Magnetic Interference (EMI) produced by an offending device so that the device may continue in use without the need to restrict the provision of power to the offending device. 
     SUMMARY OF THE INVENTION 
     Accordingly, one aspect of the present invention is drawn to an outlet unit for providing a supply voltage to the prongs of a plug comprising a housing having a plurality of electrically conductive plug channels for receiving the prongs of the plug, a shutter rotatably mounted to the housing and operative in one of a first and a second position, the shutter having openings for receiving the prongs of the plug wherein only when in the second position the openings of the shutter and the plug channels are aligned permitting axial displacement of the prongs into the housing, and a strike plate located between the housing and the shutter for preventing the rotation of the shutter to the second position absent axial displacement of the prongs sufficient to engage the strike plate. 
     Another aspect of the present invention is drawn to An apparatus for converting a DC input signal to one or more AC output signals comprising a timer/control for emitting modulated timing and logic control signals, and a power converter for receiving the modulated timing and control signals comprising a plurality of master chopper oscillators responsive to the modulated timing and control signals so as to alter the voltage of the DC input signal for output as a single phase of one of the AC output signals, a plurality of current limiting chopper oscillators responsive to the modulated timing and control signals so as to alter the voltage of the DC input signal for output as a single phase of one of the AC output signals, a current integrator in electrical contact with one of the AC output signals the current integrator capable of measuring current drawn from the AC output signal and modifying the control signals of the current limiting chopper oscillators so as to shorten the duration of time of each positive or negative voltage phase of the AC output signal. 
     The above-stated objects, features and advantages will become more apparent from the specification and drawings that follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an ISPS in accordance with the present invention. 
     FIG. 2 is a diagram of a pseudo sine wave output signal of the present invention. 
     FIG. 3A is an exploded view of an outlet unit in accordance with the present invention. 
     FIG. 3B is an isometric view of the outlet unit of FIG. 3A, with bezel removed. 
     FIG. 3C is front view of the outlet unit of FIG. 3A, with bezel removed. 
     FIG. 3D is an isometric view of a housing of the outlet unit of FIG. 3A, with contacts installed. 
     FIG. 3E is back view of the housing of the outlet unit of FIG. 3A, with contacts installed. 
     FIG. 4 is an isometric view of a power contact of the outlet unit of FIG.  3 A. 
     FIG. 5 is an isometric view of a sensor contact of the outlet unit of FIG.  3 A. 
     FIG. 6 is an isometric view of the outlet unit of FIG.  3 A. 
     FIG. 7 is a schematic diagram of an output converter and timer/control of the present invention. 
    
    
     DETAILED DESCRIPTION 
     With reference to FIG. 1, there is illustrated in block diagram form the progression from a 400 Hz/115VAC input signal  10  into an EMI Filter  11  to a PFC (Power Factor Correction)  13  to a 155VDC Converter  15 . The 155VDC output  16  as illustrated is converted to a 155VAC output for use in an ISPS. With regard to the present invention, there follows a description of the elements which combine in operation to form the power converter and outlet unit. 
     The EMI Filter  11  serves to filter out conducted Electro-Magnetic Interference (EMI) out of the ISPS. The EMI filter  11  filters out EMI that might travel from load drawing devices back into the aircraft&#39;s power supply and find its way into flight critical electrical devices. Connected to the EMI filter  11  is the PFC  13  that serves to eliminate current harmonics present in the ISPS. Connected in series with the PFC  13  is the 155VDC converter  15 . The 155VDC converter  15  serves to convert the 400 Hz/115VAC input signal into a 155VDC signal. EMI filter  11 , PFC  13 , and 155VDC converter  15  may be assembled from any number of commercially and readily available components known in the art. 
     Output converter  17  receives 155VDC output  16  and converts it into a 115VAC output signal  111 . While illustrated herein as consisting of a single 155VDC output  16  being converted into a single output signal  111 , there may in practice be a plurality of 155VDC outputs connected to a plurality of output converters  17  which in turn output a plurality of output signals  111 . Such an alteration to the configuration of the present invention described herein would be readily ascertainable to one skilled in the art. With reference to FIGS. 1 and 7, output converter  17  is comprised, in part, of current integrator  12 , master chopper oscillators  71 , current limiting chopper oscillator  73 , and EMI filter  11 ′. 
     It is the purpose of the output converter  17  to output a pseudo sine wave on output line  111  for use by electrical devices. The operation of the components of the present invention which interact to produce the required pseudo sine wave  211  is described herein with reference to FIGS. 1,  2 , and  7 . As is illustrated, the output converter receives a 155VDC signal and outputs output signals  111 . While illustrated as receiving a 155VDC input signal and outputting a 60 Hz 155VAC signal, an output converter  17  of the present invention is not so limited. Rather an output converter  17  of the present invention could be readily modified to convert a range of input DC voltages to an output AC signal of the same or different voltage wherein the frequency of the output signal may likewise be chosen from a wide range of desired frequencies such as 220VAC, 50 Hz as commonly available in Europe and 240VAC, 50 Hz as commonly available in Australia. 
     Referring to FIG. 1, while illustrated as a box, plug-in detect  19  is comprised of circuitry and hardware disclosed more fully in the text which follows. Plug-in detect  19  determines whether or not a valid plug attempt has been successfully completed. If a plug has been correctly inserted into an outlet unit of the present invention, the plug-in detect will direct timer/control  23  via a high logic signal to turn on the output converter  17 . As used herein, a “high logic” condition is one in which the voltage of a signal is sufficiently high to be interpreted as a boolean  1  for purposes of performing boolean logic. The ground fault interrupt senses the current differential through the power cord of a plugged in device back to ground. Similarly, if the ground fault interrupt  7  does not sense a substantial current differential through the power cord of a plugged in device back to ground, a high logic signal is directed to timer/control  23 . Auxiliary power source  21  provides the power to timer/control  23  required to power the logic circuits contained therein and which are described more fully in the following. System available logic  25  directs a high logic signal to timer/control  23  when there is power available for distribution to a power requesting load device. Timer/control  23  effectively performs an AND function on the input signals received from system available logic  25 , plug-in detect  19 , and ground fault interrupt  7 . In the event that all such input signals correspond to a high logic signal, timer/control  23  proceeds to emit a 240 Hz timing signal for input into the output convertor  17 . 
     Under normal operating conditions, output converter  17  makes use of several chopper oscillators  71 ,  73  to segment the incoming 155VDC signal, alter the voltage of the segments into a pseudo sine wave for output, and output the newly constructed 155VAC signal as output signal  111 . With reference to FIG.  7  and FIG. 2 there is now described the operation of power converter  17  to produce output signal  111 . 
     Timer/control  23  is comprised in part of a 240 Hz signal generator. As can be seen in FIG. 2, the pseudo sine wave of output signal  111  is comprised of four phases. Each of the four phase requires a different logic input to direct the master chopper oscillators  71  and the current limit chopper oscillators  73  to pull the output signal  111  to a voltage defined by one of the four phases. Because each full cycle of the output signal  111  requires four phases, and each phase change occurs at a single clock cycle or control signal of the 240 Hz signal generator, the resulting output signal is a 60 Hz signal (240 Hz divided by 4). 
     As is illustrated, timer/control  23  outputs four logic switch control signals SC 1 , SC 2 , SC 3 , and SC 4 . SC 1  and SC 2  control the operation of master chopper oscillators  71 . Similarly, SC 3  and SC 4  control the operation of current limiting chopper oscillators  73 . When the timer/control  23  sends a logic high signal to any of the switch controls, the corresponding switches are closed thereby altering the output voltage of output signal  111 . In phase 1, SC 1  and SC 2  are activated. In phase 2, SC 2  and SC 4  are activated. In phase 3, SC 1  and SC 4  are activated. In phase 4, SC 1  and SC 3  are activated. Under normal operating conditions, signals sent from the timer/control  23  to the chopper oscillators  71 ,  73  of output converter  17  result in the 60 Hz 155VAC pseudo sine wave signal detailed in FIGS. 2 a  and  2   b . At 60 Hz, the duration of each phase of the four phase output signal cycle is approximately 4.17 ms in duration. As a result, pseudo sine wave  211  yields a 110V rms signal as well as the same (155V) peak voltage as would a true 110V rms sine wave. 
     The power system of the invention is particularly useful to provide power to personal devices carried by a passenger onto a vehicle, such as an aircraft, ship or bus. In particular, the vehicle is a commercial aircraft. An exemplary load device for drawing power from the present invention is an AC-adapter laptop computing device. Such laptops utilize rectified peak detectors which are also typically transformer isolated. Because the peak voltage of a true sine wave is equivalent to the peak voltage of the pseudo sine wave  211 , the inductive currents in the transformers of such laptop loads will be approximately the same. A true 110VAC sine wave has an average voltage of 99V (computed as 110V*sqrt2*2/pi). Because pseudo sine wave  211  is at ±155V for two phases of each cycle and at 0V for the remainder, use of the pseudo sine wave  211  creates 22% less average voltage (77.5V) in the adapter transformers than would a true 110VAC sine wave. Therefore, the output pseudo sine wave of the present invention provides at least 75 W of power to devices attached so as to receive the output signal while remaining below the FAA mandated maximum power limit of 100 W for use in aircraft. In the present invention as will be described more fully below, the power provided through the pseudo sine wave  211  is limited to a maximum of 80 W through the interaction of the current integrator  12 , the timer/control  23 , and the current limiting chopper oscillators  73 . 
     Current input signal  711  senses the current flowing through L 1  to output signal  111 . Current input signal  711  is received by current integrator  12  which integrates over a single phase the amount of current flowing through output signal  111  to a load device receiving power. Should the amount of current outputted to a device over a single phase, for example phase 1 as illustrated in FIG. 2 a , exceed the amount of current which may be provided such that the total power draw of the device remains under the allowed 80 W, the current integrator  12  can function to reduce the power consumption of the device. Specifically, in the event that the maximum allowable current for a cycle has been outputted to a device, the current integrator toggles the control signals sent by timer/control  23  to SC 3  and SC 4 . Such a toggle could be achieved by XORing a logic high signal with SC 3  and SC 4 . When such a toggle is performed before the usual 4.17 ms duration of a single phase, pseudo sine wave  211  returns from either ±155V to 0V earlier than usual. This phenomena is illustrated in FIG. 2 a  by the dotted lines representing a leftward shift, or prematurely occurring onset, in the voltage change from +155V to 0V and from −155V to 0V. As noted, while in phase 1, SC 2  and SC 3  are on. If SC 3  is toggled off and SC 4  is toggled on, the resulting SC 2  and SC 4  being on is the condition that brings about phase 2 in which the voltage drops from 155V to 0V. Similarly, while in phase 3, SC 1  and SC 4  are on. If SC 4  is toggled off and SC 3  is toggled on, the resulting SC 1  and SC 3  being on is the condition that brings about phase 4 in which the voltage rises from −155V to 0V. In this manner, the power supplied to a load device is maintained below a designated maximum value, for example 80 W. Once either SC 3  or SC 4  is toggled and the voltage is brought to 0V, the next 240 Hz signal from the timer/control  23  does not alter the switch control settings but rather maintains them as they were. 
     In addition to safe guarding against a load device drawing an excessive amount of power, the present invention similarly prevents any load from drawing a peak amount of current in excess of a predetermined amount. Typically, such a predefined peak amount of current is approximately 3 amps. If the peak current drawn by a load device reaches such a predefined peak current amount, SC 3  and SC 4  are provided with a control circuit signal between approximately 100 and 200 KHz which is then used to pulse width modulate the output signal  111 . 
     Referring once again to FIG. 1, output converter  17  is includes EMI filter  11 ′. As noted above, each output converter may support multiple output signals  111  for use by a plurality of load devices. For example, a single output converter  17  may provide power via two output signal lines  111  to two laptop computers connected as load devices. Each laptop may produce EMI which could potentially be transmitted to the other laptop via the output converter  17 . To prevent such an occurrence, each output converter  17  includes an EMI filter  11 ′ connected so as to filter any EMI which might pass from one load to another via a single output converter  17 . When combined with the EMI filter  11  noted above, each device is shielded from EMI coming from the main power source, is prohibited from injecting EMI back into the aircraft&#39;s other systems, and is shielded from EMI originating at the site of other devices plugged into the same ISPS unit. 
     The outlet unit of the present invention is illustrated with reference to FIG.  3 . Outlet unit  41  is comprised generally of bezel  31 , torque springs  32 , shutter  33 , strike plate  35 , pressure springs  36 , fastening pins  43 , housing  37 , sensor contacts  38 , power contacts  39 , printed circuit board  34 , and cap  40 . When assembled and in static mode, bezel  31  is fastened to housing  37  through the use of fastening pins  43  inserted through holes located at peripheral points near opposing corners and extending through bezel  31  and mating with receiving cavities  45  formed integral to housing  37 . 
     Once assembled, shutter  33  rests generally flush with bezel  31 . Torque springs  32  are attached to shutter  33  in such a fashion as to exert a radial torque upon shutter  33  sufficient to rotationally displace shutter  33  around axis  47 . In its static configuration, the resting position of shutter  33  is such that torque springs  32  are least extended and shutter  33  is rotated around axis  47  such there is no correspondence between the openings in shutter  33  and the openings of strike plate  35 . As a result, there is no continuous opening through which the prongs of a plug could be inserted through shutter  33 , through strike plate  35  and into housing  37 . 
     Continuing with the discussion of the static arrangement of the outlet unit  41 , the outward facing face of strike plate  35  is pressed away from housing  37  and into contact with shutter  33  by a plurality of pressure springs  36 . Pressure springs  36  are disposed between the housing  37  and strike plate  35 . When pressed by pressure springs  36  into maximal contact with shutter  33 , tabs located on the underside of shutter  33  and extending a short ways axially towards housing  37  engage slots  49  cut into the periphery of strike plate  35 . Strike plate  35  is attached to housing  37  in such a way as to not permit axial rotation about axis  47 . Therefore while strike plate  35  can extend back and forth a short distance along axis  47 , it cannot rotate about axis  47 . When strike plate  35  is maximally extended by pressure springs  36  against shutter  33 , the slots  49  engage the tabs of shutter  33  so as to prevent the axial rotation of shutter  33 . Only when strike plate  35  is sufficiently displaced along axis  47  towards housing  37  such that slots  49  no longer engage the tabs of shutter  33  can shutter  33  be radially displaced such that the openings through shutter  33  correspond to those of strike plate  35 . 
     With reference to FIG. 4 there is illustrated a power contact  39  of the present invention. Power contact  39  is comprised in part of opposing sides  46  and back plate  48 . When positioned behind housing  37  as shown in FIG. 3A, the prongs of an inserted plug will contact the gently outwardly sloping ends of opposing sides  46  forcing a slight outward deformation of opposing sides  46 . This slight outward deformation causes the opposing sides  46  of the power contact  39  to apply pressure against the plug prong and thus maintain physical and electrical contact with the prong. Depending on the configuration of the prong, the prong may also form a contact with back plate  48 . As opposing sides  46  and back plate  48  are fashioned from the same piece of electrically conductive material, contact with either opposing sides  46  or back plate  48  is sufficient to enable electrical contact between the power contact  39  and the prong. 
     With reference to FIG. 5, there is illustrated a sensor contact  38  of the present invention. Contact sensor  38  is constructed of a single piece of electrically conductive material. Contact sensor  38  is comprised in part of contact hook  51 . When positioned behind housing  37  as shown in FIG. 3, the prongs of an inserted plug will contact contact hook  51  forming a slight outward deformation of contact hook  51 . The resulting deformation will cause contact hook  51  to exert pressure against the prong of the plug so as to assure both physical and electrical connectivity between the sensor contact  38  and the plug prong. 
     With continued reference to FIG. 3A, both power contacts  39  and sensor contacts  38  are positioned to receive and maintain contact with the prongs of a plug. In addition, both power contacts  39  and sensor contacts  38  are provided electrical connectivity to printed circuit board  34 . Printed circuit board  34  contains circuit traces capable of carrying electrical impulses to the plug-in detect  19  of FIG.  1 . To avoid exposure and subsequent connectivity to any external element, power contacts  39 , sensor contacts and  38 , and printed circuit board  34  are enclosed between housing  37  and cap  40 . Cap  40  is attached to housing  37  by means of a bolt, screw, adhesive, or other apparatus capable of providing sufficient attachment force sufficient to avoid the separation of cap  40  from printed circuit housing  37 . 
     With reference to FIG. 6, there is illustrated a perspective view of outlet unit  41  in its static state in accordance with the present invention. As used herein, static state refers to the configuration of an outlet unit  41  absent the insertion of the prongs of a plug. As described above, shutter  33  through which the prongs of the plug are to be inserted is rotated approximately 45 degrees about its center. When the prongs of a plug are inserted with through the holes in the face of shutter  33 , they come into physical contact with strike plate  35 . As described, strike plate  35  is pressed outwards against the back side of shutter  33  by pressure springs  36 . When the prongs of a plug are inserted through shutter  33  and into contact with strike plate  35  with sufficient force, the force exerted upon strike plate  35  by pressure springs  36  is counter balanced and the strike plate  35  is moved axially back towards the housing  37 . When the strike plate  35  has been so moved sufficiently, the engage slots  49  of the strike plate  35  extend so as to no longer engage the tabs attached to shutter  33  and shutter  33  is able to rotate such that the openings through shutter  33  are in correspondence with those of strike plate  35 . 
     As used herein, a “plug channel” is the empty space through which the prongs of a plug may be inserted. The plug channels of the present invention are formed from the openings in the shutter  33 , the strike plate  35 , through the housing  37 , and on till the power and sensor contacts  38 , 39 . As the inserted prongs of a plug proceed further into the plug channel, each prong contacts a power contact  39  and then a sensor contact  38 . The power contact  39  is not initially activated to provide power. The power contact  39  remains off until the control circuitry of the plug-in detect  19  attached to the sensor contact determines that power is to be provided. The control circuitry senses electrical continuity between the power contact  39  and the sensor contact  38  provided by the prongs of the plug and ensures that such continuity is provided along both prongs within a predetermined time, nominally 200 milliseconds of each other. Preferably, this predetermined time is between 0 and 300 milliseconds and more preferably, between 150 milliseconds and 250 milliseconds. Only if such continuity is established within this timeframe is current enabled to flow through the power contacts. When removing a plug, the sensor contacts  38  can sense that that the plugs are no longer in contact with them as the plug is pulled out. As a result, the flow of current can be stopped prior to the plug passing past the power contacts  39 . In this manner, the presence of arcing is avoided when a plug is removed. 
     Prior art outlet units typically rely on mechanical micro-switches to sense the insertion of a plug before providing power. In an aspect of the present invention, the plug itself is used to test for continuity with no need for additional mechanical switches. In other implementations, prior art outlets make use of a plug case sensor. The plug case sensor requires constant pressure upon it provided by the case of the inserted plug to cause power to be provided. Such a system is unreliable as aircraft vibration may partially evacuate an otherwise engaged plug through which current may and should still flow. The plug of the present invention is capable of operation without a plug case sensor and therefore does not suffer from the noted deficiency of plug case sensors. 
     In addition, after turning a plug through the required 45 degree angle of the present invention and then inserting the plug until electrical contact is made between the prongs of the plug and the sensors  38 ,  39  of the outlet, there remains a substantial residual torque arising from the predilection of the outlet unit to return to its 45 degree offset. This torque provides for a secure fitting of the plug of a device into an outlet unit  41  and resists the tendency to become loose as a result of prolonged exposure to aircraft vibration. 
     With reference to FIG. 3A, there is illustrated the pattern of openings extending through shutter  33  through which the prongs of a plug may be extended. These openings need not match the precise openings required by only a single class of plugs to facilitate the insertion and extension of the prongs of the plug through shutter  33  and into contact with sensor contacts  38  and power contacts  39 . Rather, as is illustrated, the openings in the shutter  33  preferably form a superposition of the openings required for a plurality of plug classes. Such classes include, for example, the generally rectangular cross-section of a United States prong and the generally circular cross-section of a European prong. In this manner, an outlet unit  41  of the present invention may serve as a universal outlet constructed to receive the prongs of a variety of plug classes and provide power thereto.