Patent Publication Number: US-6343050-B1

Title: Analog clock driven by radio signals with automatic resetting means

Description:
The present invention is directed to an analog clock driven by radio signals with automatic resetting means. 
     BACKGROUND OF THE INVENTION 
     An analog clock is by definition one which uses a dial face with hour and minute markings and a set of hands to indicate the hour and minute and second. Such timepieces are constructed using a chain of wheels with a proper gear ratio such that as a seconds wheel rotates it progressively turns the minutes wheel and then the hour wheel and thus rotates the hands which are fixed to the shafts of the wheels. The seconds wheel is typically coupled to a stepper motor that is controlled by an associated integrated circuit. Electrical pulses are input to the stepper motor causing the seconds wheel to turn in synchronization with the incoming pulses. In the United States, a radio station WWVB sends a time-coded signal which can be used to control either analog clocks or digital clocks so that the time is always in synchronization with the actual broadcast radio time. Such signal includes the change to and from Daylight Savings Time to automatically reset a clock receiving such signal. 
     If a clock temporarily malfunctions or its power source is removed, then of course, the clock must be reset. With a digital clock and display this can be done electronically. However, with an analog clock without modification, the driving circuit cannot know what is the erroneous setting of the analog clock display in order to correct it. Prior techniques have used feedback systems incorporating either magnetic or optical means to sense the actual positions of the hands of the analog clock. This is expensive and may not always function adequately. 
     If the user of the clock is required to reset the time, it is time consuming and in any case, the time accurate to the nearest second is not achievable. 
     Specifically, one technique of resetting analog hands is using a setting wheel incorporated in the wheel chain so that it is locked into the minutes wheel during setting. A knob fixed to the shaft of the setting wheel for rotation by a user. The minute wheel also rotates the hour wheel at {fraction (1/60)}th of its own speed, and thus the time can be set. This setting method is cumbersome involving too many rotations. Also, since only the minute wheel is set, seconds cannot be set successfully. 
     Another method is to reset the analog clock electronically by the use of a setting button. Pressing of the button causes the stepper motor to automatically rotate the minute wheel at a relatively fast speed. The user stops at the appropriate time. Again the seconds cannot be adequately set and since only the minutes wheel is actuated, a long time as much as 60 seconds may be required to set the hour hand across a 12-hour span. 
     All of the foregoing defeats the purpose of an automatically radio controlled clock. 
     OBJECT AND SUMMARY OF THE INVENTION 
     It is a general object of the present invention to provide an analog clock driven by radio signals with automatic resetting means. 
     In accordance with the above object, in a clock display driven by a radio signal providing an actual radio time, such display has an analog clock and display driven by the radio signal and a contiguous digital clock and display. A method of automatically resetting to the actual radio time the analog clock displays without use of feedback, either electrical or mechanical, from the analog display comprising the steps of stopping the analog and digital display and providing user manual controls which allow the user to set the digital display time to the displayed analog time which has been stopped. Thereafter the digital display is compared to the actual radio time and, if less, the analog clock is run at a fast rate until the displayed time is equal to the actual radio time; if more, the analog clock is run at a slow rate until equal. When equal, the analog clock is run responsive to the radio time. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a clock display showing a combined analog and digital display in one condition; 
     FIG. 2 is a plan view of the clock display in another condition; 
     FIG. 3 is block diagram of the electrical circuitry associated with the present invention; 
     FIG. 4 is a flow chart illustrating the operation of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a plan view of a clock display having an analog display portion  11  with hour, minute and second hands indicating a time of 10 hours, 12 minutes and 35 seconds and a digital display  12  indicating a time of 12:38.00. As indicated by the radio signal logo at 13, the digital display is driven by a radio signal from, for example, radio station WWVB and indicates the true or actual radio time. Thus, because of battery failure or malfunction the analog clock display  11  is erroneous. 
     FIG. 2 illustrates the same clock display but with digital display  12  showing the actual analog time which is being displayed. Also in the digital display at 14 is a “AN” indicator indicating that analog calibration will be carried out to automatically and electronically reset the analog display to the actual radio time. 
     FIG. 3 is the electronic circuit associated with the analog clock and display  11 ′ and digital clock and display  12 ′. As discussed above, the analog clock  11 ′ is driven on a line  16  by stepper motor pulses, 1 per second, which are provided by microprocessor  17 . This microprocessor is connected to a receiver and processor  18  which via the antenna  19  receives radio signals from WWVB. All of the foregoing is well-known. Microprocessor  17  on line  21  also drives the digital clock and display  12 ′ in a manner well known. Associated with the digital clock and display is a user control panel  22  where, as indicated by the labeled buttons,“SET” “▴” and “▾” may be used to set the hours, minutes and seconds, into the digital display  12  by the user. A separate button named “STEP” is used to step the second hand. User control panel  22  also contains an analog calibration switch  23  labeled ON/OFF whose function will be described below. User control unit  22  is, of course, connected via line  24  to microprocessor unit  17 . 
     Referring now to FIG. 4, this is a flow chart which shows the functioning of microprocessor  17  in resetting the erroneous analog display  11  illustrated in FIG. 1 to the actual radio time provided by radio signal WWVB as shown by the digital display  12 . Initially, the user, seeing this discrepancy, would set the analog calibration switch  23  to ON as illustrated in FIG.  4 . Next in step  26 , both movement of the analog and digital clock displays, are stopped. Normally, they would both be driven in synchronization with the pulses broadcast by the radio signal. Then in Step  27 , the user sets the digital time display  12  as illustrated in FIG. 2 to the currently displayed analog time. The analog calibration switch when it is switched to the ON position sets the indicator  14  as illustrated in FIG. 2 to AN, indicating that the resetting or calibration procedure is now being carried out. When the user has set the proper hours, minutes and seconds in the display  12 , in step  28  this is recognized by microprocessor  17  and the next compare step  29  is effected. The current analog time as contained now in the digital display  12  is compared to the true or current radio time as broadcast by WWVB. If this analog time is less, the branch  31  is taken and in step  32  the analog clock is run at a very fast rate through a turn on line  33  being made to step  29 . As shown by the branch  34 , if the analog time is more, then the analog clock at step  36  is run at a slow rate. When equality occurs (see returns  33  and  37  to step  29 ), it is indicated by the branch  38 . The analog clock is then run in a normal manner responsive to the radio signal as indicated in step  40  and the reset calibration switch  23  reset to OFF position. 
     Thus, the microprocessor  17  having been inputted the actual position of the analog hands can calculate that the time shown by the analog clock is fast or slow and by how much. Then sending pulses to the stepper motor to catch up for lost time or sending in less pulses per second to slow it down, the correct time indication is achieved. The microprocessor can keep track of in what position the hands are since it has received an accurate initial position. 
     The present invention, therefore, provides for automatic resetting of an analog clock without a need of optical or magnetic feedback as to the position of the hands of the clock.