Abstract:
A miniature device for moving a reference plane or point on an axis in rotational or x-y directions, particularly useful for two dimensional beam scanning. The device consists of a ferromagnetic ring surrounding a magnetic core which is flexibly mounted and suspended within it. Electric current at various frequencies is supplied to coils wrapped about and mounted within the ring. The core provides a magnetic field within the ring which defines its coordinates with respect to the ring and its coils and interacts with current applied to the coils to produce torque. The flexible mount suspending the core within the coils permits relative movement therebetween in response to the varying current.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device for providing movement on an axis in at least one direction selected from the rotational direction and the x or y direction. More particularly, the invention relates to a device suitable for controlling the movement of a beam of light, such as from a laser, to generate two dimensional repeating patterns of light. In one embodiment, the invention is useful as a scanner for moving a small spot of light across barcodes in order to read them. 
     BACKGROUND OF THE INVENTION 
     Scanners are devices which are used to control the movement of a beam of light, such as from a laser. The scanners are employed to aim optical elements such as mirrors, lenses and the like in order to reflect, collect and focus light. Scanners have found extensive application in the barcode industry. Barcodes consist of alternating light and dark bars which are used to present price or other information. One conventional method for reading them is to scan a focused beam of light in a line across the entire code. As light is absorbed and scattered by the bars, the resulting light modulation may be detected by a photodiode, for example, and processed by an electronic cash register or computer terminal. 
     In hand held barcode reading equipment compactness and simplicity of the scan mechanism are essential so the equipment can be portable. Single straight line scans are the simplest to generate and thus are often used in such equipment. 
     Orientation of the scanning beam with respect to the barcode is required however and this can slow down the reading process in either portable or fixed mount scanners. Various systems have therefore been devised to automatically scan a beam in multiple directions to overcome the need for tedious orientation. 
     U.S. Pat. No. 4,387,297 disclosed a portable scanning system in which a pair of motors and multiple drives are used to generate an omnidirectional pattern. Refinements of this device have not yet obviated the inherent clumsiness and size of the device due to the multiple drives and other equipment. Another beam scanning type device, shown in U.S. Pat. No. 4,639,070, uses an involved gear system for rotating various elements of the device. It also is quite complicated to manufacture. 
     U.S. Pat. No. 4,041,322 describes a device in which there is an angular displacement of a mirror in a single plane and at a constant speed. Several mirrors are used to provide the scanning signal at various angles. 
     U.S. Pat. No. 4,494,024, describes a spring activated motor, but it is a &#34;one shot&#34; spring driven motor in which heat is used to release torque by severing a chord. U.S. Pat. No. 3,631,274 describes a power supply in which a spring induces a voltage pulse in the coil. 
     U.S. Pat. No. 4,388,651 describes the faults of the prior art, stating that it is characterized generally by considerable complexity or by limited performance. This patent proposes to solve the problem using a single, small diameter rotating polygon mirror which is described as having increased scan efficiency by reflecting a beam from the polygon mirror facets two separate times. Examples of other systems are shown in U.S. Pat. No. 4,794,237, which employs a plurality of mirrors and a rotating disc, and in U.S. Pat. No. 4,795,224 which requires several motors and a relatively complicated prism ring which refracts light. 
     None of the prior art has yet been able to generate an appropriate optical pattern of lines to read barcodes at any orientation. Moreover, no prior art device has been found to produce omnidirectional scan patterns with a single optical element. Ideally, such a device would be small and very rapid, and could be held in one hand if constructed as a raster or omnidirectional device. It is desirable that the device be programmable to present one or more than one pattern of light with the fewest possible parts. 
     It is an object of this invention to provide a device for providing movement on an axis, such that a mirror can be attached to that axis, in order to impart combinations of rotational and x or y movement. Preferably the device imparts both movements, in order to generate a two dimensional scanning pattern produced by light reflected off on the mirror. 
     It is a particular object of the present invention to produce laser scan patterns which greatly reduce or eliminate the need for special orientation of either the barcode or the scanner in barcode reading equipment. 
     Yet another object is to provide a scanner which is programmable and yet which is small and compact, and which operates at low power. 
     In it broadest form, the object of this invention is to provide a means for aiming or positioning an optical element in synchronization with electronic signals, which may be produced by oscillators, computers, music, voice, and the like, for information gathering or demonstration or entertainment purposes. 
     Other objects will appear hereinafter. 
     SUMMARY OF THE INVENTION 
     It has now been discovered that the above and other objects of the present invention have been accomplished in the manner described below. Specifically, the invention relates to a device for providing movement on an axis in at least one direction selected from the x or y direction and the rotational direction, and preferably in several directions, preferably simultaneously. 
     The device includes a shaft member having an axis defining a rotational direction about the axis of the shaft. A magnetic core means is mounted on the shaft and centers the shaft on the axis. The shaft itself may extend in one or both directions axially or may be the center of the core. The core generates a magnetic field in a plane which defines x and y coordinates with respect to the axis. Also included is a ferromagnetic ring surrounding the core and aligned in the plane described above. The ring has a coil means for receiving a varied electric current in the coil which is wrapped about the ring. The ring is positioned to provide a low reluctance path for the magnetic field and the magnetic field is aligned to penetrate only one side of the coil which, of course, is inside the ring. Finally, means are provided for suspending the core with respect to the coil to permit relative movement therebetween in response to the varying frequency currents. Movement of the core causes movement on the shaft in at least the x-y direction or the rotational direction or combinations thereof. 
     In a preferred embodiment, the suspending means comprises at least one flat spiral spring or elastic member which flexibly mounts the core with respect to the coil. The spring provides a restoring rotational torque of the shaft about the axis. 
     In another embodiment, the device is adapted to receive a first frequency that is a resonant frequency of the mounting means in the rotational direction. It is further adapted to receive a second frequency, a resonant frequency of the mounting means in the x-y direction. It is contemplated that the device would further include frequency mixer means for supplying various frequencies to the coil, and preferably at least the two resonant frequencies to the coil. 
     In yet another embodiment, a second coil is added. This coil is annularly positioned around the magnetic core and is located in the region of the magnetic field which defines the x and y coordinates. Preferably, the coil is wound around a bobbin device which locates the annular coil between the ring and the magnetic core. Means are provided for introducing electric current into the annular coil. 
     It is further contemplated that a mirror will be mounted on the axis, and the entire device can be incorporated into a scanner system as desired. 
     It is further contemplated that another kind of optical element such as a small semi conductor laser device may be directly mounted to the axis and mounted into a scanner system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects of the present invention and the various features and details of the operation and construction thereof are hereinafter more fully set forth with reference to the accompanying drawings, where: 
     FIG. 1 is a perspective view of one embodiment, shown in combination with a laser source and a mirror, and also shows an output pattern. 
     FIG. 2 is an exploded view of a device similar to the device shown in FIG. 1. 
     FIG. 3 is a schematic view of a preferred driving mechanism showing magnetic field lines of force for a ring and magnetic core of the device shown in FIG. 1. 
     FIG. 4 is a section view taken along line 4--4 of FIG. 3, showing the direction of the current in the coil around the ring. 
     FIG. 5 is an exploded perspective view of another simpler embodiment of the present invention. 
     FIG. 6 is a exploded view of the preferred embodiment of this invention. 
     FIG. 7 is a cross sectional view of a device of the type shown in FIG. 6, in which the assembled device is sectioned. 
     FIG. 8 is a cross sectional view of an alternative embodiment of the device shown in FIGS. 6 and 7. 
     FIG. 9 is a perspective view showing arrangement of the shaft and springs under various forces caused by different frequency current in the coil. 
     FIG. 10 is an exploded perspective of yet another alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIG. 1, a laser beam is generated from a laser source 11 and is reflected by mirror 13 which, as will be described below, is moving in at least one or two dimensions to cause a pattern 15 to be reflected off of mirror 13. 
     While the present invention is admirably suited for use as a scanner with a laser source and the like, those components are not shown. The invention relates to the movement of the axis of a shaft in at least the x-y direction or the rotational direction. Specifically, shaft 17 has axis 19 and is caused by the present invention to rotate in the rotational direction as shown by arrow 21 and in the x-y plane as shown by arrows 23 and 24. 
     Shaft 17 causes mirror 13 to move in the rotational direction or the x-y plane by the magnetic rotor and coil arrangement contained in frame 25. The position of the magnet is restored by spring 27 as the magnet moves due to interaction with current in the coil at various frequencies. Ideally, the frequency of the current in the coil will cause rotation in both the rotational direction and the x-y directions. In FIG. 1, a rotating ellipse pattern is shown, but an almost unlimited number of patterns are possible. While spring 27 is preferred in this embodiment, other mounting means for flexibility suspending a core may be used. Of these, flat springs, flexible elastic members, and membranes are preferred. 
     Turning now to FIG. 2, a device similar to that of FIG. 1 is shown. The device is shown with its major components on an axially exploded view. Mounted on the shaft 17 is a magnet 29, with arrow 30 pointing in the direction of magnetization. 
     The lower end 31 of shaft 17 is supported in the base frame 25 such as shown in FIG. 5. Positioned radially from the magnet 29 is a toridal ring 35 which includes at least one winding 37, so that the ring 35 functions as a coil for cooperative action with magnet 29. Spring 27 is mounted on ring 35 through a pair of posts 32 which fit into holes 34 in the spring. The interior portion of spring 27 has a shaped slot 36 which fits over the central cooperative member 38 of magnet 29. Thus movement of magnet 29 with respect to core ring 35 will cause a restoring force in spring 27, as post 32 and hole 34 restrains movement of the spring while shaped slot 36 and central core 38 cause the inner portion of spring 27 to move with magnet 29. 
     Turning now to FIG. 3, the magnet 29 is shown with a north and south pole, generating a magnetic field of flux 39 so that ferromagnetic ring 35 provides a low reluctance path for field 39 from the north pole to the south pole. Flux lines 39 pass through the gap 41 between the magnet core 29 and the ferromagnetic ring 35 and also interact with current conducted by winding 37. 
     When current is passed through winding 37, the direction of the current on the portion of the winding 37 around the outside of torrid ring 35 will be opposite that of the current direction on the inside wall of ring 35. Note that the field 39 does not pass through the part of windings 37 on the outside diameter of ferromagnetic ring 35 making possible a torque to be generated between the magnetic core and the winding. The magnetic field produced by this winding 37 will also be contained and directed by the ferromagnetic material o ring 35. Current in coil 37 is not allowed to reach a level which would cause core 35 to reach a state of magnetic saturation. 
     When permanent magnet rotor 29 is introduced into the center of ring 35, its field will pass through the air gap 41 and enter the inside wall of ring 35. The field 39 will then be directed as shown by the arrows around the circumference and returned through the air gap near the opposite pole of the magnet, thereby finally completing its path. The field of the permanent magnet 29 does not substantially penetrate beyond the outer wall of the ring 35. If the field of magnet 29 penetrated the outer wall of ring 35, and thus through the outside coil windings 37, deflection forces would cancel and the rotor 29 would experience no torque. However, since the magnetic material or low reluctance path of ring 35 directs and contains the magnetic field 39 of magnet 29, and shields coil windings 37 passing up the outside wall of the ring 35, from the field of magnet 29. The magnetic field of magnet 29 passes only through one side of the winding. When a current carrying conductor is placed in a magnetic field which is perpendicular to the direction of the current, a force between the current and the field is produced which is mutually perpendicular to both the direction of the current and the magnetic field. Thus, as shown in FIG. 3, a force will be produced between a field 39 and the current in coil 37. As a result, magnet 29 will experience a torque which causes it to rotate. This torque is proportional to the number of turns of wire, the current carried by the coil, and the magnitude of the magnetic flux from the magnet penetrating the inside portion of the winding. Introduction of an alternating current in coil 37 will cause magnet 29 to oscillate. 
     Turning back to FIG. 2, it is noted that the magnet 29 is fitted through the central portion 38 of magnet 29 to the shaped slot 36 on spring 27, thus, as magnet 29 moves or vibrates about axis 19 of shaft 17, spring 27 opposes that motion. When an alternating current is introduced in coil 37, at a resonant frequency, in the rotation direction for spring 27, movement of the mirror 13 is caused to occur in the rotational direction. Similarly, when the current in coil 37 is at a frequency at or near the resonant frequency for movement of spring 27 in the x-y plane, movement in that direction is also achieved. Notice that mirror 13 is shown with its mounting hole for shaft 17 off center thereby creating a slightly unbalanced load for shaft 17. Said unbalanced load acts to initiate and sustain oscillating motion in the x-y dimensions when appropriate resonance frequencies are introduced into coil 37 for those modes of oscillation. 
     In another preferred embodiment, shown in FIG. 2, a second spring 49 is also mounted with post 51 through holes 53 in the same manner as spring 27 is supported by holes 34 on posts 32. Thus, excitation of the magnet 29 by current in coil 37, as previously described will be resisted by both spring 27 and spring 49 to provide the restoring forces necessary for oscillation. Selection of suitable frequencies of the current to be resonant with springs 27 and 49 will allow even greater variety in the ultimate movement of the mirror 13 in both the rotational direction and the x-y plane. 
     FIG. 6 shows the preferred embodiment of this invention, in which the first coil 37 and ring 35 is augmented with a second coil. An annular coil 45 is wound around bobbin 47, so as to present an annular winding in the plane of the magnetic field of magnetic core 29. Bobbin 47 is sized to fit in space 41 shown empty in FIG. 3 and filled with bobbin 47 in FIG. 7. 
     The second coil, annular coil 45, is also connected to an electric current source, not shown, so that a varied current can be introduced into coil 45. Again, various frequencies and wave forms will cause relative movement between magnetic core 29 and bobbin 47, primarily but not exclusively in the x and y plane. 
     When both the first coil 37 and annular coil 45 are energized with current at various independent frequencies the magnetic core 29 may be made to move in combinations of rotational and x-y directions which are not resonant frequencies of the system. This feature of the invention makes this embodiment even more versatile. 
     It is contemplated that the annular coil 45 may be the only coil associated with the device of this invention in at least one embodiment. Thus coil 37 would not be present in the device of FIG. 6, although ring 35 or some other support member would be needed to hold bobbin 47 in place. In this manner, core 29, which is suspended by springs 27 and 49 will cause mirror 13 to oscillate as previously described. 
     In FIG. 7, a complete assembly is shown with both core 37 and core 45 in place. This assembly optimizes the ability to provide movement to a mirror or other optical device on an axis. Covers 59 and 61 provide protection primarily against excessive deformation of springs 27 and 49 so that they do not exceed their elastic limit. 
     The device shown in FIG. 7 is configured to move mirror 13 in the manner shown in FIG. 1, where, for example, a laser 11 produces a two dimensional pattern 15 for use as a scanner. FIG. 8 shows substantially the same device except that shaft 17 is eliminated and mirror 67 is placed directly on the center 38 of core 29. In this configuration, a laser beam or other light can be directed toward the device along the axis of the device, rather than generally perpendicular to the axis. This modification permits even greater flexibility in design of a scanning device or any of the many uses for the device of this invention. In both cases, movement is provided on the axis of the device, by current flow in coils which are within the magnetic field of the core to cause relative movement between core and coil or coils as they are suspended by springs and the like. 
     Turning now to FIG. 9, torsion springs 27 and 49 are flat torsion springs with two spirals symmetrically arranged, so that the arrangement has four spring constants. One spring constant is in the z direction, shown along axis 19 while another spring constant is in the rotational direction shown by arrow 21. In addition, there are two spring constants, each in one of the x and y directions. X and y directions are perpendicular to each other, but actually represent angular displacements about the center of shaft 17, or 31, between the two springs at point A, which is midway between the two springs of 27 and 49. Thus, if a mirror is attached to the end of shaft 17, it may be made to execute oscillatory rotations in direction R as well as rocking or precessing motion in the x or y directions. By adjusting parameters of the spring such as stiffness, the number of turns of spirals, overall length of the spirals, and inertia of the mirror shaft system and the like, it is easy to obtain a desired rotational motion caused by the resonant frequency of the assembly in the rotational direction at a particular frequency as well as resonant motions in the x and y dimensions. This resonant rotational frequency can be made several times higher than the resonant frequency for rocking in either the x or y direction. Thus, movement of mirror on shaft 17 will produce a raster like pattern which will retrace itself as long as the current supplied through the windings 37 continues to be at resonances as described herein. 
     Shown in FIG. 10 is another version of the present invention in which mirror 13 is moved by shaft 17 a second coil 71 is wound about core 35a. Core 35a includes a nonmagnetic spacer which separates two conductive ring halves. When coil 37 is used as a drive coil, second coil 71 will function as a sensor coil. Movement of rotor 29 as previously described will induce a significant back EMF into the second coil 71, and this EMF can be detected. This will allow for feedback control of this drive coil 37 to modify motion of core 29. 
     While particular embodiments of the present invention have been illustrated and described herein, it is not intended to limit the invention and changes and modifications may be made therein within the scope of the following claims.