Abstract:
In a volumetric display, a strobe source illuminates a moving object at successive instants separated by potentially unequal time intervals. By specifying these intervals, an illumination controller achieves eye-catching visual effects suitable for advertising kiosks or other public displays. The volumetric display includes a signal generator configured to generate a first and second signals. An illumination controller interleaves these signals and provides the resulting interleaved signals to a strobe unit that is disposed to illuminate the moving object in response to the interleaved signals.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the priority date of U.S. Provisional Application Ser. No. 60/140,243 filed on Jun. 21, 1999, the contents of which are herein incorporated by reference. 
    
    
     FIELD OF INVENTION 
     This invention relates to volumetric displays and in particular, to stroboscopically illuminated rotating advertising kiosks. 
     BACKGROUND 
     There are many examples of volumetric (volume-filling) autostereoscopic (viewable with the unaided eye) 3-D display systems. For example, U.S. Pat. No. 3,140,415 (Three-Dimensional Display Cathode Ray Tube) discloses a spinning phosphor-coated flat disc which is addressed by a cathode ray gun. The spinning motion allows the display to present luminous points in three dimensions, creating a volumetric autostereoscopic display. 
     Similar results may be achieved with lasers, as disclosed in U.S. Pat. No. 5,042,909 (Real Time Three Dimensional Display with Angled Rotating Screen and Method) and U.S. Pat. No. 5,854,613 (Laser Based 3D Volumetric Display System). One or more lasers may be used to illuminate regions of a rotating helical screen to produce volumetric imagery. 
     In U.S. Pat. No. 4,319,805 (Rotary Screen for Receiving Optical Images Particularly Advertising Images), a projector shines imagery onto a rotating screen encased within a spherical enclosure. This requires costly projection optics, a large housing, and suffers from low image quality due to the screen&#39;s motion with respect to the projector. 
     However, the above volumetric displays use costly components such as lasers, computationally intensive illumination control systems, and difficult-to-manufacture display surfaces. As a result, such systems are not suitable for high-volume, publicly accessible displays such as advertising. 
     SUMMARY OF THE INVENTION 
     A volumetric display for illuminating a moving object uses a small number of inexpensive components to provide eye-catching visual effects. The resulting volumetric display is inexpensive, robust, and operable in a variety of both indoor and outdoor advertising environments. 
     In the volumetric display, a strobe source illuminates a moving object at successive instants separated by potentially unequal intervals. These instances of illumination, referred to as “illumination events,” are determined by an illumination controller on the basis of the desired visual effect. 
     To determine the sequence of illumination events, the illumination controller relies on a signal generator that generates both a first signal and a second signal. These two signals are passed to the illumination controller to be interleaved into a sequence of illumination events. In response to the sequence of illumination events, the strobe source illuminates the moving object. 
     In one aspect of the invention, the signal generator includes a sampling unit that responds to the motion of the moving object, and/or the mechanical phase, or position, of the moving object. This sampling unit thus generates a first signal having a motion frequency associated with motion of the moving object. The sampling unit can, for example, be a divide-by-N block that generates a signal having a frequency obtained by dividing the frequency associated with the motion of the moving object by an integer. Such a sampling unit thus generates a frequency that is proportional to the motion frequency. 
     In one embodiment, the volumetric display generates entertaining visual effects by generating a second signal having a phase offset relative to the first signal. This causes the moving object to appear to jump discontinuously from one spatial orientation to another spatial orientation. A phase shifted version of the first signal is conveniently generated by interrupting the input to the sampling unit, thereby changing the phase of the its output. 
     In another embodiment, the second signal has a frequency that differs from the motion frequency associated with the motion of the moving object. Such a signal can conveniently generated by an oscillator tuned to a frequency that is offset from the frequency of the first signal. More complex visual effects can be achieved by providing additional oscillators tuned to frequencies that are offset from the frequency of the first signal by differing amounts. 
     In an optional feature of the invention, the volumetric display can interact with the viewer. This feature can be implemented, for example, by providing a sensor to detect the presence, position, and/or motion of a person in the vicinity of the display. The illumination controller can then use the output of this sensor to select a suitable visual display. 
     These and other features of the invention will be apparent from the accompanying detailed description and the figures, in which: 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 shows several operating environments for installation of the volumetric display of the invention; 
     FIG. 2 shows a block diagram of the volumetric display of FIG. 1; 
     FIG. 3 shows the illumination controller and signal generator of FIG. 2; 
     FIG. 4 shows a specific implementation of the illumination controller and signal generator of FIG. 2; and 
     FIG. 5 shows examples of the manner in which the volumetric display interleaves two signals to generate a sequence of illumination events. 
    
    
     DETAILED DESCRIPTION 
     A volumetric display  10  according to the invention can be advantageously displayed for public view in a number of advertising environments, several of which are illustrated in FIG.  1 . For example, the volumetric display  10  can be positioned atop a vendor&#39;s kiosk  12 , on the front surface or in the interior of a vending machine  14 , or on a store shelf display  16 . In these and other environments, the volumetric display  10  can be seen by one or more viewers from a variety of angles. 
     In a typical embodiment, shown in FIG. 2, the volumetric display  10  includes a moving object  18  coupled to a motor  20 . The moving object  18  typically has an advertising messages on the front and back of a rectangular surface. The surface of the moving object  18 , which is typically 6″ (152.4 mm) across and 4″ (101.6 mm) high, is made of {fraction (1/16)} ″(1.6 mm) thick Plexiglas. The moving object  18  can rectangle or other essentially two-dimensional shape. Alternatively, the moving object  18  can be a curve in three dimensions, such as a helix, or a three-dimensional solid, such as a soda can. 
     To protect the moving object  18  from the elements or from inquisitive onlookers, the volumetric display  10  optionally includes a transparent display cover  22  enclosing the moving object  18 . The display cover  22  is preferably coated, or otherwise configured to increase the perceived brightness of the moving object  18 . For example, a one-way mirror, one-way glass, wavelength-specific filters, or a system of polarizers can be used for a display cover  22 . 
     The motor  20  coupled to the moving object  18  causes the moving object  18  to sweep out a display volume  23  by undergoing rapid, periodic motion. In FIG. 2, the moving object  18  undergoes rapid rotation of at least 10 revolutions per second, or ideally 20 revolutions per second. Although FIG. 2 shows a moving object  18  undergoing rotation, the coupling between the motor  20  and the moving object  18  can also result in translation, vibration, or oscillation of the moving object  18 , all of which can sweep out a display volume  23  as shown in FIG.  2 . The resulting motion of the moving object  18  can also be a combination of any of the foregoing types of motion in any direction. 
     A first sensor  24  coupled to the moving object  18  provides information concerning the rotational frequency and, optionally, the position of the moving object  18 , to a signal generator  25 . In the context of rotation, information concerning the position of the moving object  18  is embodied in the mechanical phase of the moving object  18 . 
     In response to information provided by the first sensor  24 , the signal generator  25  generates at least two signals. These signals are provided to a programmable illumination controller  26  that generates a sequence of illumination events by selectively sampling the signals and selecting particular samples with which to drive a strobe unit  28 . In the context of this description, a strobe unit  28  is any unit that illuminates the moving object  18  with a sequence of light pulses, each of which is sufficiently short, relative to the motion of the moving object  18 , to make the moving object appear to be stationary for the duration of the pulse. A strobe unit  28  can include flash lamps as well as LEDs and other light sources that emit short pulses. However, for slowly moving objects, the strobe unit  28  can be a conventional incandescent light controlled by a switch. 
     By sampling the signals and selecting from those samples in a controlled manner, the illumination controller  26  can generate eye-catching visual effects. For example, if the moving object  18  rotates at a frequency of at least 10 rps, the strobe unit  28  can illuminate the moving object  18  in a manner that: freezes the apparent position of the moving object  18 ; makes the moving object  18  appear to move at varying speeds in either direction; makes the element jump from one spatial orientation to another; makes the moving object  18  appear to have multiple elements which are rotating in an overlapping manner in the same, and or different, directions. In engineering parlance, the volumetric display  10  exploits temporal aliasing by using a programmable stroboscope to create an eye-catching three-dimensional display. 
     FIG. 3 shows an embodiment in which the signal generator  25  receives, from the first sensor  24 , a periodic signal that corresponds to the frequency of the motor  20 . In most cases, this frequency is approximately 400 Hz. The first sensor  24  can also provide information on the position of the moving object  18  directly to the illumination controller  26 . In the case of rotational motion of the moving object  18 , this position corresponds to a mechanical phase. However, it is possible to create interesting effects even without a signal, such as mechanical phase, that indicates the position of the moving object  18 . 
     Within the signal generator  25 , an input switch  30  gates the periodic signal into a divide-by-N block  32  (shown here with N=20) to create a 20 Hz signal from the 400 Hz signal provided by the first sensor  24 . In parallel, independent oscillators  34 ,  36  (such as simple 555 timers) create short pulses at frequencies close to the 20 Hz signal, such as 19 Hz and 21 Hz. The signal from the divide-by-N block  32  (the 20 Hz signal) and the signals from the oscillators  34 ,  36  (the 19 Hz and 21 Hz signals) are provided to the illumination controller  26 . 
     Within the illumination controller  26 , a first switch  37   a  samples the signal generated by the divide-by-N block  32 . Similarly, second and third switches  37   b-c  sample the signals generated by the first and second oscillators  34 ,  36 . These samples become inputs to an OR gate  38 . The output of the OR gate  38  is a single stream of illumination events generated by selectively sampling the signals generated by the divide-by-N block  32 , the first oscillator  34 , and the second oscillator  36 . The illumination controller  26  thus functions as a multiplexer that selects from three signal streams to form one output stream of illumination events. 
     The operation of the switches  37   a-c  and of the input switch  30  are under the control of a processor, such as a programmable logic array  44  or simple microcontroller, operating in conjunction with a low-frequency (typically 0.3 Hz) timer  46  to indicate a change-of-state. By controlling the operation of the input switch  30  and the sequence in which the individual switches  37   a-c  gate the various signals to the strobe unit, the programmable logic array  44  causes the illumination controller  26  to illuminate the moving object  18  in a manner that creates various eye-catching patterns. 
     In the illustrated embodiment, the illumination unit  28  includes 10 super-bright LEDs  40  controlled by a BJT switching circuit  42 . The output of the OR gate  38  is connected to the base terminal of a BJT so that when the output of the OR gate  38  is high, current from the emitter terminal of the BJT is provided to the LEDs  40 . However, using well-known drive circuitry, other light sources, such as, bright white-light flashlamps, can also be used. 
     FIG. 4 is a schematic of an illumination unit  28  under manual (pushbutton and SPST switch) mode control. In this embodiment, a viewer can push the input switch  30  to change the phase of the signal provided at the output of the divide-by-N block  32 . The illumination unit  28  includes several transistors  42 , each one driving a parallel pair of LEDs  40 . Each transistor  42  has a base driven by an output of a 3-input OR gate  32  formed by connecting the output of a first two-input OR gate to the input of a second two-input OR gate. The outputs of the first and second oscillators  34 ,  36  are passed through first and second high-pass filters  41 ,  43  before being provided to the OR gate  32  by way of the first and second switches  37   b ,  37   c.    
     Optionally, the volumetric display  10  can include a second sensor  48 , for example a motion sensor, to cause the volumetric display  10  to be responsive to the presence or motion of a viewer. The second sensor  48  can detect the presence of a viewer and/or the position of the position of one or more viewers. The second sensor  48  can then provide that information to the illumination controller  26  as shown in FIG.  2 . In response to the viewers presence or position, the programmable logic array  44  can be programmed to cause the display  10  to interact with the viewer. 
     In operation, the first sensor  24  provides an input signal having a frequency Nf as shown in FIG.  3 . If the input switch  30  is closed, the input signal passes through the divide-by-N block  32 . The corresponding output of the divide-by-N block  32  is a first signal having a frequency f. If the first switch  37   a  is closed, this first signal causes the OR gate  38  to generate a series of output pulses at a frequency f. This series of output pulses causes the illumination unit  28  to illuminate the moving object  18  with periodic light pulses at a frequency of f. If the moving object  18  rotates at a frequency that is an integer multiple of f, the moving object  18  will appear to be standing still. 
     If a viewer, a microprocessor, or the programmable logic array  44  momentarily opens and then closes the input switch  30 , the phase of the signal provided at the output of the divide-by-N block  32  will change relative to the mechanical phase of the moving object  18 . This will cause a discontinuous phase change in the output of the OR gate  38  driving the strobe unit  18 . As a result of this phase change, the moving object  18  will appear to instantaneously shift from a first spatial orientation to a second spatial orientation. 
     By applying the foregoing principle, the illumination controller  26  can be configured to cause the moving display  18  to shift from a first spatial orientation to a random second spatial orientation by randomly opening and closing the switch  37   a . Alternatively, the shift to a random second spatial orientation can be achieved by inviting a viewer to press the input switch  30 . 
     If information concerning the mechanical phase of the moving object  18  is available to the programmable logic array  44 , the discontinuous shift from the first spatial orientation to the second spatial orientation be coordinated with the motion of the moving object  18 . With this ability comes the ability to achieve additional eye-catching special effects. For example, a moving object  18  can have several faces, each of which has a different image. The orientation of the moving display  18  can then be controlled to give the effect of animating those images. 
     If the display  10  is equipped with the optional second sensor  48  as described above, then information concerning the presence and/or position of the viewer will be available. This allows the illumination controller to select the second spatial orientation on the basis of the viewer&#39;s activities, thereby permitting the wireless interaction of the moving object  18  with the viewer. For example, the viewing angle for the advertising message on the moving object  18  can be continuously adjusted to follow the viewer as the viewer moves around the display. Alternatively, the display  10  can be activated upon the approach of a viewer to attract the viewer&#39;s attention and then deactivated upon the viewer&#39;s departure to avoid premature wear and excessive power usage. 
     The input switch  30  and the divide-by-N block  32  thus cooperate to generate two signals. The first signal is a first pulse train having a frequency f and the signal is a second pulse train having the same frequency f but a different phase. These two signals can be temporally interleaved by periodically operating the input switch  30 . 
     The two temporally interleaved signals are then provided to the illumination controller  26 . Using the first switch  37   a , the programmable logic array  44  samples this stream of two temporally interleaved signals and provides those samples to the OR gate  38 . Depending on the instant that the programmable logic array  44  closes the first switch  37   a , the sample provided to the OR gate  38  can arise from either the first signal or the second signal. In response to the sample provided at its input, the OR gate  38  generates a stream of pulses, each of which defines an illumination event that originates from either the first signal or the second signal. 
     The foregoing special effects are achieved without the aid of the independent oscillators  34 ,  36  shown in FIG.  3 . The inclusion of these oscillators  34 ,  36  in the signal generator  25  and their associated their associated second and third switches  37   b ,  37   c  in the illumination controller  26  provides yet additional opportunities for eye-catching special effects. 
     In the illustrated signal generator  25 , the first oscillator  34  generates a first pulse train at a frequency f+df 1  that is slightly higher than the frequency output by the divide-by-N block  32 . This first pulse train thus forms the second signal of the signal generator  25 , the first signal being the output of the divide-by-N block  32 . The programmable logic array  44  selectively passes or withholds this second signal from the OR gate  38  by selectively operating the switch  37   b . This results in the generation of a pulse train by the OR gate  38 , each of the pulses being an illumination event arising from either the first signal, provided by the divide-by-N block  32 , or from the second signal, provided by the first oscillator  34 . 
     Under the control of the programmable logic array  44 , the first oscillator  34  and the divide-by-N block  32  can cooperate to generate a three-dimensional display in which the moving object  18  appears to rotate simultaneously in two directions at two different angular velocities. For example, the first signal can illuminate the moving object  18  at a frequency slightly lower than the rotational frequency, thus generating the effect of a moving object  18  slowly rotating in a first direction. Meanwhile, the second signal can illuminate the moving object  18  at a frequency slightly higher than the rotational frequency, in which case the moving object  18  will appear to slowly rotate in a second direction opposite the first direction. 
     The second oscillator  36  generates a second pulse train at a frequency f−df 2  slightly lower than the frequency output by the divide-by-N block  32 . Note that the frequency offsets df 1  and df 2  need not be identical. This second oscillator  36  operates in a manner identical to the first oscillator  34  as described above. This second oscillator  36 , together with optional additional oscillators operating in the same manner, can further enhance the visual display by generating additional signals having frequencies that differ from the first and second signal. 
     FIG. 5 illustrates the manner in which the OR gate  38  interleaves pulse trains having different frequencies to form a sequence of illumination events. The uppermost graph shows a first pulse train at a frequency f as generated by the divide-by-N block  32 . The second and third graphs show second and third pulse trains at slightly higher (f+df 1 ) and slightly lower (f−df 2 ) frequencies as generated by the first and second oscillators  34 ,  36  respectively. When passed through the OR gate  38 , these three pulse trains are interleaved, as shown in the bottom graph of FIG. 5, to form a sequence of illumination events. 
     By controlling the switches  37   a-c , the illumination controller  26  can further manipulate the sequence of illumination events. For example, the second switch  37   b  could be controlled so as to sample only every other pulse in the second pulse train, thereby effectively halving its frequency. This can result in sudden, and hence eye-catching changes in the appearance of the moving object  18 . 
     Although the above description contains many specifics, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention.