SYSTEMS AND METHODS FOR PROVIDING WOBBLE REDUCTION IN GALVANOMETERS

A limited rotation motor system is disclosed that includes a stator within a housing, a rotor rotatably coupled within the stator by a first bearing system at a proximal end and a second bearing system at a distal end, each of said first bearing system and said second bearing system being coupled at an inner side thereof to the rotor and being coupled at an outer side thereof to the housing, a compression system applying a compressive force between the first bearing system and the second bearing system in an axial direction, and a damping system adjacent any of the first bearing system and the second bearing system, said damping system providing that divergent forces resulting from the compressive force that diverge from the axial direction are absorbed by the damping system

BACKGROUND

The invention generally relates to motor system and relates in particular to limited rotation motor systems.

Limited rotation motor systems (e.g., galvanometer systems) may be used in galvanometer-based optical scanners. Galvanometer-based optical scanners were invented in the 19thcentury. for many years, their use was mostly limited to scientific applications. since the invention of the laser, they have become increasingly used in a growing number of industrial, scientific, medical, and entertainment applications.

Many of these applications demand that the optical scanner be able to perform at increasing levels of speed and accuracy to meet improved throughput and performance requirements. In order to meet these more stringent requirements, materials for their construction were chosen to make the scanners faster and higher performance. Typically, materials were chosen to be lighter and stiffer. These materials would raise the resonant frequencies to levels higher than the applications would easily excite. Ever increasing demands on optical scanner throughput have created faster scanning systems that more easily excite their natural resonant frequencies, either by directly driving the product at its resonance or near it by operating at fractional increments (or harmonics) of the resonant frequency.

When the resonant frequency is excited, it can cause the optical scanner to move its scanning spot outside the desired range of axial controlled motion. This unwanted motion has earned itself the name of wobble describing its cross axis oscillatory vibration.

Applications using optical scanners continue to demand high performance at ever increasing speeds. In order to meet these needs, wobble, needs to be controlled, either by reducing it to an acceptable level or by eliminating it completely. For many users of optical scanners, this is critical for them to be able to make and use optical scanning systems successfully and to remain competitive in the marketplace. There remains a need for further reducing wobble in galvanometer-based optical systems.

SUMMARY

In accordance with an aspect, the invention provides a limited rotation motor system that includes a stator within a housing, a rotor rotatably coupled within the stator by a first bearing system at a proximal end and a second bearing system at a distal end, each of said first bearing system and said second bearing system being coupled at an inner side thereof to the rotor and being coupled at an outer side thereof to the housing, a compression system applying a compressive force between the first bearing system and the second bearing system in an axial direction, and a damping system adjacent any of the first bearing system and the second bearing system, said damping system providing that divergent forces resulting from the compressive force that diverge from the axial direction are absorbed by the damping system.

In accordance with another aspect, the invention provides a limited rotation motor system that includes a stator within a housing, a rotor rotatably coupled within the stator by a first bearing system at a proximal end and a second bearing system at a distal end, each of said first bearing system and said second bearing system being coupled at an inner side thereof to the rotor and being coupled at an outer side thereof to the housing, a compression system applying a compressive force between the first bearing system and the second bearing system in an axial direction, and a damping system between the rotor and the housing and providing that divergent forces resulting from the compressive force that diverge from the axial direction are absorbed by the damping system.

In accordance with a further aspect, the invention provides a method of operating a limited rotation motor. The method includes providing a stator within a housing, providing a rotor rotatably coupled within the stator by a first bearing system at a proximal end and a second bearing system at a distal end, each of said first bearing system and said second bearing system being coupled at an inner side thereof to the rotor and being coupled at an outer side thereof to the housing, applying a compressive force between the first bearing system and the second bearing system in an axial direction, and damping divergent forces resulting from the compressive force that diverge from the axial direction by absorbing the divergent forces with an elastomeric component between the rotor and the housing.

The drawings are shown for illustrative purposes only.

DETAILED DESCRIPTION

The design of a galvanometer-based optical scanner consists of a stationary member as well as a rotating member. The rotating member is held within the stationary member by means of low friction rotational mechanisms restricting the motion to within a desired axis of revolution. Due to the rigidity of the materials commonly used, the system can have significant mechanical resonant frequencies. These resonances can be excited by the intended motions of the rotating member. If left undamped, these resonant vibrations can cause unwanted motions out of the plane of intended motion. By proper application of the use of materials with vibration damping properties in the construction of an optical scanning system, a scanning system can be built that can significantly reduce these vibrations to a level that will not detract from the intended accurate performance of the system. A goal of the design of the system is to reduce or eliminate unwanted cross axis resonant motion in galvanometer-based optical scanners to the point where it no longer degrades the intended accuracy of the system.

A magnetic driven optical scanner consists of a rotational element constrained within a housing. The example shown uses a Face to Face ball bearing preload to accurately hold and constrain the rotational elements motion into an accurately controlled axis of rotation.

The preload force is created by compressing spring against the outer race of the rear ball bearing. This axial force is split between axial and radial component forces through the angular interface of the bearings raceway and the spherical balls contained in it. The compression of the ball's transfers some of the force radially driving the balls into the edges of the raceway removing ‘slop’ and taking up internal mechanical clearances within the ball bearing structure. The axial component transfers its force through the length of the rotor where it passes similarly through a second ball bearing in a symmetric arrangement to the first.

FIG.1for example, shows a limited rotation motor system10in accordance with an aspect of the present invention that includes a rotor12within a stator14inside a housing16. The rotor includes a magnet18contained between a proximal end cap20at a proximal end24, and a distal end cap22at a distal end26. A tool such as a mirror28is coupled to the distal end cap26.

With further reference toFIG.2(which shows an enlarged view of the proximal end) andFIG.3(which shows an enlarged view of the distal end), each end cap is coupled to the housing16via one of a proximal bearing system36and a distal bearing system38. The proximal end24includes a compression spring30held by a closure plate34that applies a compressive force against a retaining ring32at the distal end. At the distal end, the axial forces pushing through the distal end of the distal bearing system38are held back by retaining ring32held in the housing16. This is the design of an optical scanner constructed using two deep grove radial ball bearings preloaded in a ‘Face to Face’ arrangement. Typically, all the materials used in this compression stack are rigid, solid materials.

This construction technique typically creates an optical scanning system of two predominately rigid, solid members: the rotating element12and the stationary member14(e.g., a densely wrapped set of conductive coiled wire). Each of these assemblies has resonant frequencies determined by the structure's geometric layout, materials, and constraining forces. Typically, these resonant frequencies are desired to be higher than frequencies that would occur during the operation of the product. However, under certain circumstances it is difficult to avoid exciting these resonances by the designed operation of the scanner.

These resonant frequency oscillations can cause the scanning system to vibrate and cause motion to occur outside of the desired single axis of revolution. In the optical scanning business, this undesired motion has earned itself the nickname of wobble. The mirror element of the optical scanner is intended to rotate purely about the scanner's axis of rotation in a manner that creates an angularly addressable position tracing out motion within one plane creating a straight line. When the mirror/shaft assembly vibrates at or near the resonant frequency, the resonant frequency can excite the flat mirror in a cantilever mode causing the scanned area of the optical field to now be at a position other than at the desired perpendicular spot within the plane of rotation. In a side cross sectional view of the mirror, this motion would appear similar to a diving board bending under a swimmer about to jump off of it. This undesired up and down motion in the optical scanner system is known as wobble. If this uncontrolled motion is undesirable for system performance, then it must be mitigated.

With reference again toFIG.2, the proximal end24further includes a compliant thrust washer40between the proximal bearing system36and the proximal end cap20, as well as one or more compliant O-rings42also between the proximal bearing system36and the proximal end cap20. Similarly, with reference again toFIG.3, the distal end24further includes a compliant thrust washer44between the distal bearing system38and the distal end cap22, as well as one or more compliant O-rings46also between the distal bearing system38and the distal end cap22.

With the addition of the above compliant materials to the preload force-stack, the excitation of the rotating members resonance can be diminished. The preload force transfers through the compliant thrust washers40,44on its way from the shaft assembly into the inner race of the front ball bearing, as shown in the close-up views ofFIGS.2(showing the proximal end) and3(showing the distal end). The compliant radial members (O-rings) are added between the shaft assembly12and the inner surface of the bearing systems' inner diameters. Slightly compressed O-rings are used in this example to hold the front diameter of the rotating shaft assembly centered within the inner diameter of the bearing. By including a clearance between the rigid surfaces of the bearing and the shaft, resonant vibrations in the radial direction can be minimized by allowing microscopic motion to occur at this interface and be absorbed by the compliant material properties of the O-rings42,46rather than through a rigidly bonded shaft to bearing contact. Silicone may also be chosen as a good material for use in the compliant thrust washer40,44and for the radially compressed O-rings42,46. The O-rings42,46may be maintained under radial pressure in the limited rotation motor system10.

The compliant thrust washers40,44ofFIGS.2and3each bear against a shoulder (41,45respectively) of an end cap20,22. Although the shoulders41,45are provided in the axial direction, they are radially offset from the central regions of the end caps against which the compressive force (Fc) is provided.FIG.3shows a diagrammatic view of the distal end of the system10, showing the compression thrust washers40,44and compression O-rings42,44(three each) between the rotor12and the housing16on the inner sides of the bearing systems36,38. The axial compression in the force stack is therefore not compromised, while the divergent forces are at least partially absorbed by the compliant thrust washers40,44. Similarly, the O-rings42,46are radially offset from the central regions of the end caps against which the compressive force (Fc) is provided. The axial compression in the force stack is again therefore not compromised, while the divergent forces are also at least partially absorbed by the compressed O-rings42,46.

As shown inFIG.4, the compressive force (Fc) of the compression spring30against the retaining ring (32shown inFIG.3) may result in divergent forces (Fd) that diverge from the axial direction. These divergent forces are absorbed by the compression system of the invention that includes, in accordance with an aspect, compliant force washers and compliant radial members such as O-rings.

The enhancement of this O-ring feature for the purpose of vibration reduction by increasing the number of O-rings42,46used and the clearance between bearing and shaft diameter, does not negatively impact the compression of the rigidity of the system in the axial direction. By adding this compliant material, microscopic vibrations in the rotating shaft assembly are provided a place to be absorbed. By allowing this vibration to be absorbed by a material with dampening properties, the amplitude of the resonant vibrations can be reduced to an acceptable level or eliminated.

FIG.5shows a distal end27of a limited rotation motor system in accordance with a further aspect of the invention that includes an axial-compressed O-ring45in place of a thrust washer (of the system ofFIGS.1-3). The limited rotation motor system similarly includes the rotor12with the stator14inside the housing16. The rotor includes the magnet18contained between proximal and distal end caps (distal end cap22is shown), with the mirror28mounted thereto. The O-rings46are radially offset from the central region of the end cap against which the compressive force (Fc) is provided. The O-rings45,46are provided on an inner surface of the bearing system38. The axial compression in the force stack is again therefore not compromised, while the divergent forces are also at least partially absorbed by the compressed O-rings46. The O-rings46may be compressed, and may be provided as one, two or three O-rings (as shown). The compressed O-ring45is mounted against an axial shoulder61of the distal end cap22.

Again, although the shoulder61is provided in the axial direction, it is radially offset from the central region of the end cap22against which the compressive force (Fc) is provided. The axial compression in the force stack is therefore not compromised, while the divergent forces are at least partially absorbed by the axial compressed O-ring45.

Any number of compression O-rings may be used, including for example, one, two or three O-rings (as shown) at each end of the limited rotation motor system. Further, the O-rings ofFIGS.1-4are shown adjacent the inner races of the bearing systems36,38in contact with the end caps20,22. In accordance with further aspects, the O-rings may be positioned radially outward such that they are adjacent the outer races of the bearing systems in contact with the housing16(as shown below with reference toFIG.8). Any number of compression O-rings may be used, including for example, one, two or three O-rings (as shown) at each end of the limited rotation motor system. Further, the O-rings ofFIGS.1-4are shown adjacent the inner races of the bearing systems36,38in contact with the end caps20,22. In accordance with further aspects, the O-rings may be positioned radially outward such that they are adjacent the outer races of the bearing systems in contact with the housing16(as shown below with reference toFIG.8). The proximal end of the limited rotation motor system may similarly include radial O-rings (e.g.,46) as well as axial compressed O-ring (e.g.,45) against a shoulder on the proximal end cap.

FIG.6shows a distal end29of a limited rotation motor system in accordance with a further aspect that includes a cross-sectionally L-shaped elastomeric material47in place of the thrust washer and axial O-rings (of the system ofFIGS.1-4). The elastomeric material47with the L-shaped cross-section is provided on the inside of the bearing against the shaft as shown inFIG.6. This feature could be a molded part installed as shown or formed in place between the shaft and bearing, or an over-molded feature on the surface of the shaft. The limited rotation motor system similarly includes the rotor12with the stator14inside the housing16. The rotor includes the magnet18contained between proximal and distal end caps (distal end cap22is shown), with the mirror28mounted thereto. The cross-sectionally L-shaped elastomeric material is radially offset from the central region of the end cap against which the compressive force (Fc) is provided. The axial compression in the force stack is again therefore not compromised, while the divergent forces are also at least partially absorbed by the cross-sectionally L-shaped elastomeric material47, which provides axial and radial absorption. The cross-sectionally L-shaped material is mounted against an axial shoulder63of the distal end cap22. Again, although the shoulder63is provided in the axial direction, it is radially offset from the central region of the end cap22against which the compressive force (Fc) is provided. The cross-sectionally L-shaped elastomeric material is provided on an inner surface of the bearing system38. The axial compression in the force stack is therefore not compromised, while the divergent forces are at least partially absorbed by the cross-sectionally L-shaped material47. The proximal end of the limited rotation motor system may similarly include cross-sectionally L-shaped elastomeric material (e.g.,47) against a shoulder on the proximal end cap.

FIG.7shows a distal end31of a limited rotation motor system in accordance with a further aspect that includes a cross-sectionally L-shaped elastomeric material49that is provided on an outer surface of the bearing system38, with the short length on the distal side of the bearing system38. The limited rotation motor system similarly includes the rotor12with the stator14inside the housing16. The rotor includes the magnet18contained between proximal and distal end caps (distal end cap22is shown), with the mirror28mounted thereto. The cross-sectionally L-shaped elastomeric material49is radially offset (even outside the bearing system) from the central region of the end cap against which the compressive force (Fc) is provided.

The axial compression in the force stack is again therefore not compromised, while the divergent forces are also at least partially absorbed by the cross-sectionally L-shaped elastomeric material49, which provides axial and radial absorption. The axial compression in the force stack is therefore not compromised, while the divergent forces are at least partially absorbed by the cross-sectionally L-shaped material49. The proximal end of the limited rotation motor system may similarly include cross-sectionally L-shaped elastomeric material (e.g.,49) mounted similarly. The L-shaped cross section of elastomer49ofFIG.7is positioned on the outside of the bearing against the housing16. This feature could be a molded part installed has shown or formed in place between the shaft and bearing, or an over-molded feature on the surface of the shaft.

FIG.8shows a distal end33of a limited rotation motor system in accordance with a further aspect that includes a thrust washer51mounted against an axially distal end of the bearing system38, as well as one or more (e.g., one, two or three) O-rings53(e.g., circular or polygonal cross sectionally shaped) mounted on the outer race of the bearing system38. The thrust wash51and O-rings53are both provided on an outer surface of the bearing system38. In particular, the thrust washer51is positioned between the side wall of the bearings outer race and the retaining ring32. The limited rotation motor system similarly includes the rotor12with the stator14inside the housing16. The rotor includes the magnet18contained between proximal and distal end caps (distal end cap22is shown), with the mirror28mounted thereto. O-rings53are radially offset (even outside the bearing system) from the central region of the end cap against which the compressive force (Fc) is provided. The axial compression in the force stack is again therefore not compromised, while the divergent forces are also at least partially absorbed by the elastomeric material51and O-rings53, which provide axial and radial absorption. The axial compression in the force stack is therefore not compromised, while the divergent forces are at least partially absorbed by the material51and O-rings53. The proximal end of the limited rotation motor system may similarly include cross-sectionally L-shaped elastomeric material (e.g.,1) and O-rings53mounted similarly.

The positions of the compression thrust washers and compression O-rings are moved to the outer sides of the bearings. The limited rotation motor system includes a rotor18within a stator14inside a housing16. Again, the system includes the compliant thrust washer and compression O-rings (e.g., three each) between the rotor end caps and the housing on the outer sides of the bearing systems. The divergent forces (Fd) diverging from the axial direction are similarly absorbed by the compliant thrust washers as well as the one or more compliant radial members such as compliant O-rings.

FIG.9shows a distal end35of a limited rotation motor system in accordance with a further aspect that includes an annular elastomeric material55that is bonded to an inner surface of the inner race of the bearing system. The bonding for example, may be provided by a silicon room temperature vulcanization (RTV) adhesive. The limited rotation motor system similarly includes the rotor12with the stator14inside the housing16. The rotor includes the magnet18contained between proximal and distal end caps (distal end cap22is shown), with the mirror28mounted thereto. The elastomeric material55is radially offset from the central region of the end cap against which the compressive force (Fc) is provided. The axial compression in the force stack is again therefore not compromised, while the divergent forces are also at least partially absorbed by the elastomeric material55, which provides axial and radial absorption. The elastomeric material55is also mounted against an axial shoulder65of the distal end cap22. Again, although the shoulder65is provided in the axial direction, it is radially offset from the central region of the end cap22against which the compressive force (Fc) is provided. The elastomeric material is provided on an inner surface of the bearing system38. The axial compression in the force stack is therefore not compromised, while the divergent forces are at least partially absorbed by the elastomeric material55. The proximal end of the limited rotation motor system may similarly include elastomeric material (e.g.,55) against a shoulder on the proximal end cap and bonded to the proximal bearing system.

The elastomeric material55is bonded between the inner race of the bearing and the shaft. The area near the shoulder65does not have elastomer (in compression) taking up axial force. The material55is adhered to both the inner race of the bearing and the outer surface of the shaft. The bonding strength of this material should have sufficient strength to withstand the shearing force of the axial directed pre-load force.

FIG.10shows a distal end35of a limited rotation motor system in accordance with a further aspect that includes an annular elastomeric material57that is bonded to an outer surface of the inner race of the bearing system. The bonding for example, may be provided by a silicon room temperature vulcanization (RTV) adhesive. The limited rotation motor system similarly includes the rotor12with the stator14inside the housing16. The rotor includes the magnet18contained between proximal and distal end caps (distal end cap22is shown), with the mirror28mounted thereto. The elastomeric material57is radially offset from the central region of the end cap against which the compressive force (Fc) is provided. The axial compression in the force stack is again therefore not compromised, while the divergent forces are also at least partially absorbed by the elastomeric material57, which provides axial and radial absorption. The axial compression in the force stack is therefore not compromised, while the divergent forces are at least partially absorbed by the elastomeric material57. The proximal end of the limited rotation motor system may similarly include elastomeric material (e.g., similar to57) mounted at the proximal end.

Retaining rings (again having circular or polygonal cross-sectional shapes) may be used with the above systems, although with the systems that include the annular elastomeric material that is bonded in place, retaining rings may not be required. With reference again toFIGS.1and4, limited rotation motor systems in accordance with various aspects of the present invention may include any combination of the above damping elements as part of dynamic damping systems, for example, with proximal and distal ends including different combinations of O-rings (axial and radial), thrust washers, cross-sectionally L-shaped material and annular elastomeric material, both mounted radially inwardly or outwardly.

Again, each of the elastomeric features discussed above may be provided on any or both of the proximal and distal ends of limited rotation motor systems in accordance with various aspects of the present invention. The elastomeric features may be molded parts that are installed, or formed in place between the shaft and bearing, or an over-molded features on the surface of the shaft or the inner surface of the housing.