Patent Publication Number: US-6984951-B2

Title: Drive assembly for a covering of an architectural opening

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation of U.S. patent application Ser. No. 10/062,969, filed on Jan. 30, 2002 now U.S. Pat. No. 6,781,335, which corresponds to and claims benefit to European application number 01300816.4, filed Jan. 30, 2001. U.S. application Ser. No. 10/062,969 and European application number 01300816.4 are both hereby incorporated by reference as though fully set forth herein. 

   BACKGROUND OF THE INVENTION 
   a. Field of the Invention 
   The invention relates to a drive assembly for a covering of an architectural opening, comprising a motor drive, an accumulator connected to the motor drive, a power source and an electrical circuit connecting the power source to the accumulator. 
   b. Background Art 
   Light regulating devices, such as retractable and extendable awnings and control systems for automatically extending such awnings are known. 
   Motor driven venetian blinds comprising either vertical or horizontal slats are known, which can be opened by retracting the slats to one side of the window and in which the position of the slats around their longitudinal axis can be controlled electrically via a control unit, which blinds are powered from the main power supply. 
   BRIEF SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a drive assembly for a covering of an architectural opening, which can be operated electrically and which can be powered by a relatively low current or voltage power source. 
   It is in particular an object of the present invention to provide a drive assembly which can be operated by a photovoltaic cell of relatively small dimensions and operating at low light level conditions. 
   It is again an object of the present invention to provide a drive assembly using an electrical circuit connecting the power source to the accumulator, which is self-starting and which uses a relatively small number of components. 
   It is a further object of the present invention to provide a drive assembly having an electrical circuit in which power losses are minimized and which is of compact design. 
   It is still a further object of the present invention to provide a drive assembly with an electrical circuit, which can operate at or near the maximum power point of a solar cell. 
   Thereto, the drive assembly according to the present invention is characterized in that the electrical circuit comprises a step-up converter. 
   The step-up converter transforms the small fluctuating voltage or current derived from the power source to DC current ranging from 1-20 V, suitable for charging the accumulator for operating the motor drive. Use of the step-up converter allows the drive assembly to be powered by a solar cell of small dimensions, which may be mounted for instance at the inside of a window on the head rail of a venetian blind, facing towards the inside of the building, or being placed on any position on the windowsill. 
   An embodiment of the drive assembly according to the present invention comprises a step-up converter with an input terminal connected to the power source and an output terminal with a supply voltage, connected to the accumulator, the step-up converter circuit having:
         an input terminal for connection to a varying voltage or current source, and an output terminal with a supply voltage,   an inductive element being with a first terminal connected to the input terminal and with a second terminal to a capacitive element and to the output terminal, the capacitive element being with one terminal connected to a reference voltage,   a first switch being with a first terminal connected to the second terminal of the inductive element, and with a second terminal to the reference voltage, the first switch comprising a gate electrode for opening and closing of the switch when a control voltage of a first level is applied to the gate,   an oscillator comprising a power input connected to the output terminal, a start-up output connected to the gate electrode of the first switch for supplying a pulse-like signal to the gate electrode and an oscillator output.       

   The energy from the power source is stored in the inductive element and is periodically charging the capacitor for forming and increasing supply voltage on the output terminal. This increasing supply voltage is fed into the oscillator, which output signal rises as a consequence resulting in better control of the switch and hence more power being input into the capacitive element, such that the voltage of the output terminal is increased. 
   In a preferred embodiment, the step-up converter further comprises a second switch connected in parallel with the first switch, the second switch having a gate electrode connected to the oscillator output, wherein the first switch remains opened when the supply voltage at the output terminal reaches a predetermined level, and the second switch is operated by the oscillator output at a second voltage level that is higher than the first voltage level. 
   The varying input voltage is fed into the inductive element, which is periodically connected to reference voltage by opening of the first switch under control of the start-up output of the oscillator. The power input of the oscillator is connected to the supply voltage terminal, which at start-up receives a very small voltage. The resulting start-up output voltage is correspondingly small, for instance 0.2 V or less. When the first switch is opened and closed again, a rising current is generated in the inductive element, which charges the capacitive element such that the supply voltage is successively increased. The first switch is particularly suited to be operated at a low gate control voltage from the start-up output of the oscillator. As the supply voltage increases, the start-up output signal of the oscillator will increase, resulting in better operation of the first switch and more power being transferred from the inductive element to the capacitive element, such that a self-amplifying effect results in increasing the supply voltage and the oscillator start-up output signal. When the supply voltage reaches a predetermined value, the first switch is de-activated (opened) and the second switch is operated from a second oscillator output, at a gate control voltage, which is above the gate control voltage of the first switch. Operation of the second switch results in a further increase in the supply voltage. The first switch may for instance be formed by a bipolar pnp-transistor with a gate control voltage of 0.6 V above reference voltage, a collector-emitter voltage Vce of 600 mV at a collector current Ic of 100 mA. The second switch may be formed by a low power logic level MOSFET with a gate control voltage Vgs (gate threshold voltage) generally in the range of 1-2 V at a source voltage Vds of 2 V and at a current Ids of 0.3-1.2A. 
   By the use of the two switches according to the present invention, each operating at a different gate control voltage level, a self-starting step-up converter is achieved. 
   In one embodiment, a diode is connected between the second terminal of the inductive element at the gate electrode of the first switch. When a varying supply voltage of about 0.4 V is offered to the input terminal, and the supply voltage is about 0.4 V, a 0.4 V bias voltage on the control terminal of the first switch is maintained by the positive clamp formed by the diode. Hence, in case the first switch is formed by a pnp bipolar transistor, only a 0.2 V varying control voltage is necessary at the gate to bring the transistor into conduction. The 0.2 V varying voltage is obtained from the oscillator when powered at its input by a 0.4 V supply voltage level. 
   In a further embodiment, the outputs of the oscillator are connected to the gates via respective capacitive elements. By the capacitive element coupling, the small DC control voltage from the start-up output of the oscillator is added to the 0.4 V DC level of the diode clamp. 
   A voltage converting unit may be formed by attaching a second converting stage to the voltage converting circuit, the second converting stage having an inductive element with a first terminal connectable to the varying voltage source, and connected with a second terminal to a first terminal of an electrical element such as an accumulator, the accumulator being with a second terminal connected to the reference voltage, a third switch being connected between the second terminal of the inductive element and the reference voltage and being with a gate electrode connected to an oscillator output of a second oscillator, the supply voltage of the output terminal of the voltage converting circuit being connected to the second terminal of the inductive element and to a power input of the second oscillator. The third switch may be formed by a power MOSFET having multiple drains and multiple sources for further converting the DC-voltage from the converting circuit to levels of between 3-15 V. 
   The voltage converting circuit according to the present invention may be applied in combination with a solar cell as a power source, a fuel cell or other varying voltage or current sources having relatively small current and voltages at their output. The voltage-converting unit according to the present invention may be part of a cattle watering unit, country road lighting or an electrical fence in the countryside when as a voltage source a solar cell is used. Other applications in combination with a solar cell are digital billboards, billboard lighting, street lighting or information points. 
   Furthermore, the device of the present invention can be used to power speed control devices along roads, roadside reflectors or road markings (cat eyes), emergency points, etc. 
   Alternatively, the voltage converting circuit can be applied in marine applications as a generator on boats, for boat lighting, as a navigation device or a GPS-system. 
   Mobile phones, laptops, organisers, and other appliances may be powered by the voltage converting circuit which only needs a very small voltage input. 
   Furthermore, digital cameras, battery chargers, bicycle lighting, danger triangles, avalanche beepers, flashlight, tv&#39;s, microwaves and other domestic appliances, garden lighting, garden sprayers and light regulating devices for windows, such as window blinds, awnings and etc., may be powered by the voltage converting circuit of the present invention. 
   The invention is most beneficial to small sized appliances by allowing a substantial reduction in surface of the solar cells. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Some embodiments of a voltage-converting unit according to the present invention will be explained in detail with reference to the accompanying drawings. In the drawings: 
       FIG. 1  shows an architectural covering device according to the present invention comprising a pleated light regulating device; 
       FIG. 2  shows an architectural covering device according to the present invention comprising a venetian blind; 
       FIG. 3  shows schematically the drive assembly according to the present invention; 
       FIG. 4  schematically shows an assembly of a voltage converting circuit according to the present invention in combination with a DC—DC step-up voltage converter connected to an electrical device; 
       FIG. 5  shows in detail the components of the voltage converting circuit and DC—DC converter of  FIG. 1 ; 
       FIG. 6  shows an alternative embodiment of a voltage converting circuit according to the present invention wherein the second switch is controlled by a microprocessor; 
       FIG. 7  shows a schematic diagram of the input and output voltages of the inverters U 1C  and U 1E ; 
       FIG. 8  shows an input voltage of inverter U 1C  during start-up; and 
       FIG. 9  shows an output voltage of inverter U 1C  during start-up. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a wall  40  having a window  41  along the upper end of which a head rail  42  of a pleated window covering  43  is mounted. On the head rail a drive assembly  44  is mounted comprising an array of photovoltaic cells (solar cells)  45  facing towards the interior of the wall  40 , an electric drive assembly  46  comprising a drive motor, an accumulator and a step-up converter connecting the accumulator to the solar cells  45 . The assembly  46  can be completely integrated into the head rail  42  or can be provided as a separate unit attached to the wall  40 . Control unit  48  for raising or lowering the window covering  43  is connected to the drive assembly  46 . 
     FIG. 2  shows an alternative embodiment of a window covering comprising a vertically deploying venetian blind, having horizontal slats  50  suspended from a head rail  42 . Solar cells  45  are mounted on a windowsill and connected through electrical leads  51  to drive assembly  46 . By operation of the control unit  48  the slats  50  may be raised or lowered or may be changed in orientation by rotating around their longitudinal axes. 
     FIG. 3  schematically shows a drive assembly according to the present invention, comprising an electric motor  52  for raising or lowering the window covering and/or changing the orientation of the slats  50 , an electrical circuit  53 , an accumulator or battery  54 , a step-up converter  55  and a photovoltaic cell  45 . The electrical circuit  53  may comprise a step-up converter for increasing the voltage derived from the battery  54 . The battery  54  may comprise a metal hydride accumulator, an alkaline manganese battery, a lithium ion battery, or a plurality of lithium ion batteries in series. 
   In an embodiment, the accumulator has a capacity not exceeding 1.4 Ah. The battery may be a 3.6 V battery system, whereas the electric motor  52  may operate at 12 V DC at the power requirement not exceeding 50 mWh per day. 
   In a preferred embodiment the active operation of the electric motor  52  does not exceed 40 s per day. 
     FIG. 4  shows a step-up voltage converting unit  1  having a voltage converting circuit, or low voltage converter stage  2 , connected to a second converter stage  3 . The low voltage converter stage  2  comprises an input terminal  4 , an inductive element  5 , first and second switches  6 ,  7  and a capacitive element such as capacitor  8 . Switches  6  and  7  are with a first terminal connected to the inductive element  5  and with a second terminal to a reference voltage line  9 . The second terminal of capacitive element  8  is connected to the output of a diode  11  and to the supply voltage terminal  12 . The supply voltage terminal  12  is connected to a power input  14  of a first oscillator  13 . A start-up output  15  of the first oscillator  13  is connected to the base or gate electrode  31  of switch  6  whereas the oscillator output  16  is connected to the gate electrode  32  of switch  7 . The supply voltage at an output terminal  12  of low voltage converter stage  2  is connected to the second terminal of inductive element  28  and to a power input  22  of second oscillator  17  of second converter stage  3 . The oscillator output  18  connects to the gate electrode  33  of switch  19 . A diode  20  and capacitive element or capacitor  21  are connected between the inductive element  28  and reference voltage line  23 . Electrical device  24  is connected across output terminals  25 ,  26  of second converter stage  3 . 
   When at start-up a varying low voltage supply, such as a solar cell, is connected to input terminals  4  and  27  of the voltage converting unit  1 , and switches  6 ,  7  are closed, the capacitive element  8  is charged, creating a small voltage on the output terminal  12  and on first oscillator power input  14 . The small power input into the oscillator  13 , results in a pulse shaped signal on start-up output  15  at a low gate control voltage level V C1 , which may be a few tenths of volts, periodically opening and closing the switch  6  at the frequency of for instance 100 kHz. This causes a periodic current through the switch  6  resulting in a rising current through the inductive element  5 , charging capacitor  8  that is rectified by diode  11  and results in an increasing voltage at the supply voltage terminal  12  and consequently at the power input  14  of the first oscillator  13 . This effect continues until the voltage level at supply terminal  12  reaches a predetermined level, after which low voltage controlled switch  6  is de-activated (opened) and high voltage controlled switch  7  is operated from oscillator output  16 . The second switch  7  is operated at a control voltage level V C2  until the supply voltage at supply voltage terminal  12  is for instance a few volts. The supply voltage is input into second converter stage  3  at the second terminal of inductive element  28  and into power input  22  of second oscillator  17 . At oscillator output  18 , a pulsed control signal operating the gate electrode  33  of switch  19  is generated. By switching on and off the switch  19 , the energy stored in inductive element  28  is transferred to capacitor  21  until a predetermined voltage level is reached. At this predetermined level, such as voltage levels between 1.5-12 V, switch  19  is opened such that electrical energy is stored in inductive element  28 , to be released again upon closing of the switch  19 . 
   As the step-up voltage-converting unit  1  generates its own supply voltage from a situation of rest, the step-up converter is self-starting. 
     FIG. 5  shows in detail the components of the voltage converter stage  2  and second converter stage  3  according to the present invention. The following letter symbols apply:
     T 1  low power, logic level MOSFET;   T 2  switching MOSFET; power MOSFET;   L 1  switching coil with high inductance;   L 4  switching coil;   D 1 , D 2  rectifying diodes;   C 9 , C 21 , C 1  smoothening electrically controllable capacitors (elco&#39;s);   U 1A -U 1F , U 1C  low voltage inverter gates manufactured by Philips Electronics under type number 74HC14;   T 4  switching bipolar transistor;   D 2 , D 4  Schottky diodes;   C 3  relatively small capacitor.   
   The second converter stage  3  operates according to known DC—DC voltage converter principles according to which the small fluctuating voltage V-solar at the input of coil  28  is stored in the coil when switching MOSFET  19  is opened. Upon closing of the switching MOSFET  19 , the energy is released from the coil  28  and supplied via rectifier diode  20  to smoothing capacitors  21  resulting in an increased voltage across output terminals  25 ,  26 . In order to be self-starting, voltage converter circuit or step-up circuit  2  is provided wherein the oscillator  13  is constructed of active component of the type of Philips low voltage inverter ports or gates U 1C  and U 1E . The inverter ports can generate at their output, voltages at an input voltage of V CC  of below 0.4 V at start-up. 
   At low supply voltages V CC , transistor T 3  is switched-off and a very low alternating voltage is supplied via start-up output  15  of oscillator  13  to a coupling capacitor C 2 , and from thereon to the base  31  of transistor T 4 . Schottky diode D 4  is used as a positive clamp such that a small alternating voltage appears on the base  31  with an offset of 0.4 V. The solar cell voltage is about 0.4 V. The transistor T 4  will go in conduction at a gate voltage of about 0.6 V, such that the gate voltage need only be 0.2 V in order to get transistor T 4  into conduction. It has appeared that the oscillating inverter gate U 1C  of oscillator  13  can supply enough energy to get the transistor T 4  into conduction. This causes a periodic current in the collector c of transistor T 4 . Since the transistor T 4  is coupled with a switching coil with a relatively high inductance L 1  and a relatively small capacitor C 3 , the periodic current in the collector c results in an AC voltage across the coil  5 . This AC-voltage is rectified through Schottky diode D 2  and appears on supply voltage terminal  12  and is fed back at the supply of low voltage inverter gates U 1C -U 1F . Each time V CC  rises, the voltage level at the start-up output  15  of the oscillator  13  rises, resulting in better control of switching transistor T 4 . Proper gating of transistor T 4  results in more power being stored in coil  5 , increasing supply terminal voltage V CC  etc. At the outlet  30  of the oscillator U 1C , a coupling capacitor C 4  is provided which operates a low voltage inverter gate U 1E . The output of the oscillator U 1E  is connected to the control gate  32  of a low power logic level of the MOSFET T 1 . The coupling capacitor C 4  ensures that the MOSFET of T 1  switches at the beginning or start-up in phase with transistor T 4 . 
   When the supply voltage V CC  rises above the threshold level of logic level MOSFET T 1 , transistor T 3  goes into conduction, pulling the input of oscillator U 1C  to ground such that first transistor T 4  is switched-off and logic level MOSFET T 1  takes over. Now V CC  can rise to for instance 3 V wherein the final power conversion up to voltages ranging from 1.5-12.0 V is effected by power MOSFET T 2  of second converter stage  3 . When V CC  reaches its desired end level, the varying supply level V-solar will place transistor T 5  in conduction pulling the input of oscillator U 1F  to ground and de-activating switch T 2 . 
     FIG. 6  shows another embodiment of a low voltage solar converter including a step-up DC—DC converter (sometimes also called: a voltage increasing chopper). The main components of the step-up converter are: inductor/inductance L 4 ; semiconductor switch T 4  and supplemental N-channel MOSFET T 2 ; diode D 1  (Schottky ZHCS 750) and capacitor/capacitance in the form of high capacity elco C 23  compensated for low resistance by additional capacitors C 19  and C 20 . Semiconductor switch T 4  operates the step-up converter at those times when the voltage is too low to operate the MOSFET switch T 2 . Switch T 4  is operated by an oscillator circuit as indicated in  FIG. 3  by a dash-dotted box. The output of the oscillator connects to the start-up oscillator connector of the step-up converter where Schottky diode D 3  (ZHCS 750) adds the output voltage of the solar panel  425   a  to the pulsed voltage generated by the oscillator. The resulting voltage is offered to the base of T 4 . As soon as the voltage offered to the step-up converter is high enough for the MOSFET switch T 2  to operate, the oscillator output is grounded through semiconductor T 3  of the oscillator circuit. Then the MOSFET T 2  is controlled from the “N-gate” output of the central micro processor  471  and a further P-channel MOSFET T 1  is controlled from the “P-gate” output of the processor  471  to take over from the Schottky diode D 1 . The P and N-gates of the processor  471  are software driven. In this manner a particularly advantageous step-up converter has been obtained. The alternative use of semiconductor switches T 4  and T 2  provides for a register of compound step-up converter that has optimal characteristics for each of a low voltage and a higher voltage range. The use of Schottky diode D 3  enables to offer an as high as possible voltage to the base of the low voltage semiconductor switch T 4 . The additional MOSFET switch T 1 , which is positioned in parallel to diode D 1 , allows to eliminate the losses, which normally occur in diodes such as D 1 . 
     FIG. 7  shows the input and output voltages V 1 , V 0  of inverter ports U 1C  and U 1E  which are inverting Schmitt-trigger inverter ports. Generally, at a supply voltage V CC  of 1 V, the negative-going threshold V T1  will be about 0.5 V, the positive-going threshold V T2  being several tenths of Volts higher. The output voltage V 0  will be limited to a maximum of supply voltage V CC . The inventors have found out that at supply voltages V CC  below specification of the manufacturer, there is a region of the inverter port below V T1  at which at low supply voltage V CC  there still is a hysterises in the output signal such that an oscillator can be obtained by feedback of the output signal to the input via resistor R 2 . At a supply voltage of V CC  0.4 V the input at the inverter gate U 1C  is given in  FIG. 8 , at a level of about 300 mV, at a frequency of about 4 kHz. 
   In  FIG. 9 , the output at inverter gate U 1C  is given at a level of 400 mV with a frequency of about 20 kHz. Surprisingly, at low supply voltages V CC  and at low input levels below the negative-going threshold V T1  according to specifications, it is still possible to obtain an oscillator using inverter gate U 1C  such that start-up of the step-up converter can be obtained by use of said component.