Abstract:
A laser marker/pointer for projecting circular or elliptical laser beam patterns onto a target surface such as a portion of a presentation screen or to assist in the aiming of a firearm, comprises a handheld shell body in which is mounted a laser light source, a rotating optical mirror driven by a motor, and an electronic drive circuit, whereby the aspect ratio of the marking pattern is determined by the geometric relationship of the motor shaft axis, the laser beam, and the mirror surface. The motor drive circuit when initially powered (along with the laser diode), applies full power (a continuous DC voltage to the motor to overcome inertia), followed by a pulsed voltage to lower the duty cycle of the motor, increase battery life, and reduce rotational noise.

Description:
FIELD OF THE INVENTION 
     The present invention is related generally to laser pointers, and more specifically to laser markers operable for projecting circular or elliptical illuminated patterns. 
     BACKGROUND OF THE INVENTION 
     In conference and meeting presentations, a presenter often uses a laser pointer to highlight portions of a projected viewgraph or slide presentation so that an associated oral message can be better understood by the audience. The conventional laser pointer projects only a small bright spot. The typically small sized spot can be difficult to distinguish when projected upon a large screen. Another disadvantage for a laser pointer often is the brightness of the spot, so that can make viewers very uncomfortable if their eyes focus on the spot. 
     An illuminated spot may also be used to assist in the aiming of a firearm to improve targeting accuracy during hunting. The small size of the mark can also be a disadvantage as it is difficult to be noticed far away. 
     A few modified laser pointers have been developed. For example, U.S. Pat. No. 5,450,148 uses a set of selectable masks to filter a magnified laser output into a desired pattern. U.S. Pat. No. 5,400,514 teaches a way to create light geometric tracing through moving a light source in one or two dimensions. None of above solutions provides a simple way to generate circular or elliptical patterns. 
     SUMMARY OF THE INVENTION 
     The primary object of this invention is to provide a laser pointer/marker that can generate a circular or elliptical pattern. The size of the pattern is proportional to the distance between laser pointer and illuminated target. A presenter can shine a large size circular or elliptical pattern on the projected screen display to highlight key messages more clearly to the audience. Similarly, a hunter can quickly identify the projected pattern on the target. 
     In the preferred embodiment of the present invention, an elliptical laser tracing pattern is achieved through reflection of a coherent laser light from a tilted rotating mirror positioned off the central axis of the laser beam. The device comprises three key parts, namely a laser diode, a rotating mirror, and an electronic circuit to drive the motor. A collimated light beam emitted from the laser diode impinges upon and is reflected from the face of a mirror. A small motor driven by an electronic circuit unit rotates the mirror. The mirror is tilted slightly from the perpendicular plane to the motor longitudinal axis of the shaft. The reflected light beam follows the rotational movement of the mirror and generates an elliptical shape that is projected onto the screen display. The electronic drive circuit initially provides full power to overcome the initial inertia and to start the motor. After a predetermined time, the electronic circuit reduces the duty cycle to conserve the battery energy, and lowers the rotational noise at the same time. 
     The relative spatial and angular arrangement of the longitudinal axis of the motor and the laser beam can alter the elliptical shape, or provide a circular shape. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the invention are described with reference to the drawings in which like items or components are identified by the same reference designation wherein: 
         FIG. 1  is an illustration of a preferred embodiment of the laser pointer/marker of the present invention; 
         FIG. 2  is a schematic diagram of a representative embodiment of an electronic circuit for driving the mini motor; 
         FIG. 3  is a diagram to describe the spatial and angular relationship of the mirror, the mini motor, and the laser beam; 
         FIG. 4  illustrates a cut-away view for the mounting part for the electrical motor  26  or the laser diode  16  in  FIG. 1 ; and 
         FIG. 5  is a waveform diagram showing the application of voltage to drive the motor from turn-on to a reduction in duty cycle over the time period of operation for one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1 , the preferred embodiment of a device  11  according to the present invention for generating circular and elliptical laser patterns comprises a handheld housing or shell body  10 , laser diode unit  16 , mirror  22 , electric motor  26 , electric circuit board  32  to drive the motor  26 , batteries  36  and  38 , and a switch  34  operable for actuating device  11  by applying power from batteries  36 ,  38  to motor drive circuit  32  and laser diode unit  16 . 
     The external shell body  10  houses the components of the device  11 . The shell body  10  is typically cuboid shaped with rounded edges but can also use other more esthetically appealing curvy shapes. A laser diode beam generating unit  16  is powered by two batteries  36  and  38  controlled by an electric switch  34 . The switch on the shell body  10  is positioned at a location for users to conveniently access. The diode laser unit  16  is attached to the shell body  10  by a mounting part  18 , and motor  26  by a mounting part  28 . A cut-away view of the mounting parts is shown in  FIG. 4 . 
     The positive terminal  40  from series connected batteries  36 ,  38  is individually connected to an arm of switch  34 , and the negative terminal  42  to a generally shown electrical connection strip  35 . The pole or output of switch  34  is connected to connection strip  35 . The motor drive circuit  32  is connected via connection strip  35  to the pole of switch  34  and negative terminal  42 . Also, the pole of switch  34 , and negative terminal  42  are connected via a two conductor cable  20  to laser diode unit  16 , via connection strip  35 . Also, a two conductor cable  30  connects the motor drive circuit  32  via connection strip  35  to motor  26 . Note that the use of connection strip  35  is not meant to be limiting in that other connection means can be used. 
     Operation of the present laser marker device  11  will now be described. The emitted diode laser beam  37  impinges on a mirror  22  and is reflected to generate the output beam  44 . The output beam  44  passes through an optical window  45  at one end of the shell body  10  (see  FIG. 1 ). The mirror  22  is affixed to a wedge shaped substrate  24 . The substrate planar surface  25  facing the electrical motor  26  is perpendicular to the motor shaft  27 , allowing the planar mirror face  29  to be slightly tilted. The detailed geometry of the mirror  22 , laser diode  16 , and motor  26  will be described in more detail below. The electric motor  26  rotates the tilted mirror  22  to generate the desired circular/elliptical patterns. 
       FIG. 2  shows a representative circuit schematic diagram of the circuit board  32 . The circuitry  32  uses a CMOS timer  46  (an LMT 555, for example) in the Astable Multivibrator mode to generate a pulsed output. The ratio of resistor value of R b  to R a  determines the duty cycle of the output pulse. One unique feature of the circuitry is the inclusion of a resistor R c  and a capacitor C 2  to the reset pin  4  of the 555 CMOS timer  46 . The resistor R c  and capacitor C 2  enable the circuit to run the electric motor at 100% of duty cycle for a short fixed time (˜R c ×C 2 ) when the circuit is activated by closure of switch  34 . This feature enables the motor  26  to draw a higher level of current to overcome the initial mechanical inertia. After the motor  26  starts and the capacitor C 2  is fully charged, the operation of the circuitry is changed to a pulse width modulator mode with a greatly reduced duty cycle to sustain the movement of the motor  26 . The circuitry design of circuit board  32  offers the benefits of a lower motor rotational noise and the reduced power consumption. In the astable mode of operation, current flows from batteries  36 ,  38  through resistor R a , and the low resistance path provided by forward biased diode  43  to charge capacitor C 1 . When Capacitor C 1  is charged to a given level, it then discharges through resistor R b  into discharge terminal  7  of the 555 CMOS timer  46 . Diode  43  enables the astable mode duty cycle to be determined by the ratio of R b  to R a . Diode  48  suppresses electrical spikes generated by mini motor  26  as it rotates, thereby protecting the associated circuitry from damage. More specifically, the circuit components connected as shown in  FIG. 2  includes switch  34  (momentary pushbutton SPST switch in this example); series connected batteries  36  and  38  (alternatively can be a single 3 VDC battery, for example); resistors R a  (8.2KΩ), R b  (1.2KΩ), R c  (220KΩ), and R d  (387Ω); capacitors C 1  (470 nF), and C 2  (1 μF); transistor  50  (a Darlington TIP125, for example); a micro motor  26  (Part No. F-K20, Voltage: 1V-7.5V, speed −17,500 rpm at 3 volts/42,000 rpm at 7.5 volts); diodes  43  and  48  (each IN4004); and laser diode  16  [Part No. DRM506-D006; 650 nm 5 mW (Red) Laser Dot Module; a product of Optical Line Power]. Note that the laser diode  16  is provided in this example as a module that includes driver circuitry (not shown), and the laser diode  16 . The component values and numbers are from an operable prototype of the present laser marker  11 , and are not meant to be limiting. 
       FIG. 3  provides details of the geometric relationship among the laser diode  16 , the electric motor  26 , and the mirror  22 . Line AD is the direction of laser beam  37  emitted from laser diode  16 . Point D is the position where the laser beam  37  impinges on the mirror  22 . Line BD is perpendicular to the surface of mirror  22 . Line CDG is the central line or longitudinal axis of the shaft of electrical motor  26 . The angle between laser beam  37  (also line AD) and motor shaft axis CDG is denoted by α. The angle between line BD and motor shaft axis CDG is denoted by β. For a projection screen  50  that is perpendicular to the center axis DH of the output circular/elliptical cone  52 , the aspect ratio L r  of the laser trace pattern  44  projected from mirror  22  can be estimated by the following equation: 
                     L   r     =       tan   ⁡     (     2   ⁢   β     )         tan   (       cos     -   1       (     1       1   +     4   ⁢     (       cos   2     ⁢   α     )     ⁢     (       tan   2     ⁢   β     )             )     )               (   1   )               
Obviously, for a screen  50  that is not perpendicular to the cone axis, the aspect ratio of the laser trace pattern is changed by the screen surface angle to the cone axis DH.
 
       FIG. 5  is a waveform diagram showing that upon closure of switch  34  at time t 0 , thereafter, during an initial time period T 1  (200 ms, for example) full power or voltage of VDC level is applied to motor  26 . After capacitor C 2  charges, the CMOS timer  46  enters into an astable mode of operation for applying a pulsed voltage to motor  26  of zero volts during time periods T 2  (2.7 ms, for example), and V DC  during time period T 3  (0.3 ms, for example). When switch  34  is opened, capacitor C 2  discharges through timer  46  to ground, and the drive voltage to motor  26  is terminated at time t 1 . 
     Although various embodiments of the invention have been shown and described, they are not meant to be limiting. Those of skill in the art may recognize various modifications of these embodiments, which modifications are meant to be covered by the spirit and scope of the appended claims.