阅读说明：本技术 一种具有多曲面融合回转体结构的壳体振动陀螺谐振子 (Shell vibrating gyro harmonic oscillator with multi-curved surface fused revolving body structure ) 是由 石云波 刘俊 蔡麒 曹慧亮 唐军 申冲 赵锐 于 2021-02-24 设计创作，主要内容包括：本发明涉及壳体振动陀螺,具体是一种具有多曲面融合回转体结构的壳体振动陀螺谐振子。本发明解决了现有壳体振动陀螺抗冲击能力差、品质因数低、加工工艺复杂、控制成本高的问题。一种具有多曲面融合回转体结构的壳体振动陀螺谐振子,包括谐振质量、支撑座、四个驱动电极、四个驱动模态反馈电极、四个检测电极、四个检测模态补偿电极；其中,谐振质量为开口向上的圆杯状结构；谐振质量的底壁中央开设有上下贯通的中心圆孔；谐振质量的底壁边缘开设有八个上下贯通的隔离圆孔,且八个隔离圆孔围绕谐振质量的中心线对称分布。本发明适用于航空、航天、航海、工业、农业、交通等领域。(The invention relates to a shell vibration gyro, in particular to a shell vibration gyro harmonic oscillator with a multi-curved surface fused revolving body structure. The invention solves the problems of poor shock resistance, low quality factor, complex processing technology and high control cost of the existing shell vibration gyro. A shell vibration gyro harmonic oscillator with a multi-curved surface fusion revolving body structure comprises a resonance mass, a supporting seat, four driving electrodes, four driving mode feedback electrodes, four detection electrodes and four detection mode compensation electrodes; wherein the resonance mass is a circular cup-shaped structure with an upward opening; a vertically through center round hole is formed in the center of the bottom wall of the resonance mass; eight isolating round holes which are communicated up and down are formed in the edge of the bottom wall of the resonance mass, and the eight isolating round holes are symmetrically distributed around the center line of the resonance mass. The invention is suitable for the fields of aviation, aerospace, navigation, industry, agriculture, traffic and the like.)

1. A shell vibration gyro harmonic oscillator with a multi-curved surface fusion revolving body structure is characterized in that: the device comprises a resonance mass (1), a supporting seat (2), four driving electrodes (3), four driving mode feedback electrodes (4), four detection electrodes (5) and four detection mode compensation electrodes (6);

wherein the resonance mass (1) is a round cup-shaped structure with an upward opening; the center of the bottom wall of the resonance mass (1) is provided with a center round hole (7) which is communicated up and down; the edge of the bottom wall of the resonance mass (1) is provided with eight isolation round holes (8) which are communicated up and down, and the eight isolation round holes (8) are symmetrically distributed around the center line of the resonance mass (1);

the side wall of the resonance mass (1) comprises a lower section side wall and an upper section side wall; the side wall of the lower section is in a cone-shaped structure, and the diameter of the side wall of the lower section is gradually increased from bottom to top; the side wall of the lower section is provided with eight isolating bar holes (9) which are communicated from inside to outside and are arranged along the direction of a bus, and the eight isolating bar holes (9) are symmetrically distributed around the center line of the resonance mass (1); the central lines of the eight isolating bar holes (9) are intersected with the central lines of the eight isolating round holes (8) in a one-to-one correspondence manner; the side wall of the upper section is of a spherical belt structure, and the diameter of the side wall of the upper section is gradually increased from bottom to top;

the supporting seat (2) is of a circular cup-shaped structure with a downward opening, and the supporting seat (2) is coaxially fixed on the edge of an upper end orifice of the central circular hole (7); the center of the top wall of the supporting seat (2) is provided with an installation screw hole (10) which is communicated up and down;

the four driving electrodes (3), the four driving mode feedback electrodes (4), the four detection electrodes (5) and the four detection mode compensation electrodes (6) are all of a strip-shaped sheet structure, and the four driving electrodes (3), the four driving mode feedback electrodes (4), the four detection electrodes (5) and the four detection mode compensation electrodes (6) are all piezoelectric ceramic electrodes polarized along the thickness direction;

the negative electrode surfaces of the four driving electrodes (3) and the negative electrode surfaces of the four detection mode compensation electrodes (6) are all fixed with the outer bottom wall of the resonance mass (1), and the four driving electrodes (3) and the four detection mode compensation electrodes (6) are all arranged along the radial direction; the four driving electrodes (3) and the four detection mode compensation electrodes (6) are symmetrically distributed around the central line of the resonance mass (1); the four driving electrodes (3) are correspondingly positioned between the first isolation round hole (8) and the second isolation round hole (8), between the third isolation round hole (8) and the fourth isolation round hole (8), between the fifth isolation round hole (8) and the sixth isolation round hole (8), and between the seventh isolation round hole (8) and the eighth isolation round hole (8); the four detection mode compensation electrodes (6) are correspondingly positioned between the second isolation round hole (8) and the third isolation round hole (8), between the fourth isolation round hole (8) and the fifth isolation round hole (8), between the sixth isolation round hole (8) and the seventh isolation round hole (8) and between the eighth isolation round hole (8) and the first isolation round hole (8);

negative electrode surfaces of the four driving mode feedback electrodes (4) and negative electrode surfaces of the four detection electrodes (5) are fixed with the outer side wall of the lower section of the resonance mass (1), and the four driving mode feedback electrodes (4) and the four detection electrodes (5) are arranged along the direction of a bus; four driving mode feedback electrodes (4) and four detection electrodes (5) are symmetrically distributed around the central line of the resonance mass (1); the four driving mode feedback electrodes (4) are correspondingly positioned between a first isolating bar hole (9) and a second isolating bar hole (9), between a third isolating bar hole (9) and a fourth isolating bar hole (9), between a fifth isolating bar hole (9) and a sixth isolating bar hole (9) and between a seventh isolating bar hole (9) and an eighth isolating bar hole (9) one by one; the four detection electrodes (5) are correspondingly arranged between the second spacing bar hole (9) and the third spacing bar hole (9), between the fourth spacing bar hole (9) and the fifth spacing bar hole (9), between the sixth spacing bar hole (9) and the seventh spacing bar hole (9), and between the eighth spacing bar hole (9) and the first spacing bar hole (9).

2. The shell vibration gyro harmonic oscillator with the multi-curved surface fused solid of revolution structure of claim 1, wherein: the resonance mass (1) and the supporting seat (2) are both made of Ni-Span-C Alloy 902 constant elasticity Alloy.

3. The shell vibration gyro harmonic oscillator with the multi-curved surface fused solid of revolution structure of claim 1, wherein: the piezoelectric ceramic is PZT-5H piezoelectric ceramic.

4. The shell vibration gyro harmonic oscillator with the multi-curved surface fused solid of revolution structure of claim 1, wherein: the negative electrode surfaces of the four driving electrodes (3) and the negative electrode surfaces of the four detection mode compensation electrodes (6) are fixed with the outer bottom wall of the resonance mass (1) through conductive adhesive; the negative electrode surfaces of the four driving mode feedback electrodes (4) and the negative electrode surfaces of the four detection electrodes (5) are fixed with the outer side wall of the lower section of the resonance mass (1) through conductive adhesive.

5. The shell vibration gyro harmonic oscillator with the multi-curved surface fused solid of revolution structure of claim 1, wherein: the thickness of the bottom wall of the resonance mass (1) is 0.8 mm; the thickness of the lower section side wall of the resonance mass (1) is 1mm, and the length of a bus is 10 mm; the thickness of the upper section side wall of the resonance mass (1) is 1.2mm, the height is 7.5mm, and the outer diameter is 30 mm; the thickness of the supporting seat (2) is 0.5mm, and the height is 4.2 mm; the four driving electrodes (3) and the four detection mode compensation electrodes (6) are all 5.6mm in length, 1.6mm in width and 0.2mm in thickness; the lengths of the four driving mode feedback electrodes (4) and the four detection electrodes (5) are all 9mm, the widths of the four driving mode feedback electrodes and the four detection electrodes are all 1.6mm, and the thicknesses of the four driving mode feedback electrodes and the four detection electrodes are all 0.2 mm; the diameter of the central circular hole (7) is 4 mm; the diameters of the eight isolating circular holes (8) are all 2 mm; the hole distances between the eight isolation circular holes (8) and the central circular hole (7) are all 5 mm; the length of each of the eight isolating bar holes (9) is 9mm, and the width of each of the eight isolating bar holes is 2 mm; the diameter of the mounting screw hole (10) is 2 mm.

6. The shell vibrating gyroscope harmonic oscillator with the multi-curved surface fused solid of revolution structure of claim 5, wherein: the first-order natural frequency of the resonance mass (1) is 1516.7Hz, the second-order natural frequency is 1531.6Hz, the third-order natural frequency is 4385.2Hz, the fourth-order natural frequency is 4385.4Hz, the fifth-order natural frequency is 5305.2Hz, the sixth-order natural frequency is 5425Hz, the seventh-order natural frequency is 11813Hz, the eighth-order natural frequency is 11814Hz, the driving mode frequency is 4385.4Hz, and the detection mode frequency is 4385.2 Hz.

Technical Field

The invention relates to a shell vibration gyro, in particular to a shell vibration gyro harmonic oscillator with a multi-curved surface fused revolving body structure.

Background

The shell vibration gyro has the advantages of high precision and low power consumption, and is widely applied to the fields of aviation, aerospace, navigation, industry, agriculture, traffic and the like. The specific working principle of the shell vibrating gyroscope is as follows: when no angular velocity is input, the harmonic oscillator of the shell vibrating gyroscope works in a driving mode, and the output of the shell vibrating gyroscope is zero. When the angular speed is input, the harmonic oscillator of the shell vibrating gyroscope works in a detection mode, and the shell vibrating gyroscope measures the input angular speed in real time. However, practice shows that the existing shell vibration gyro is limited by the geometrical structure of the harmonic oscillator, so that the problems of poor impact resistance, low quality factor, complex processing technology and high control cost generally exist. Based on the above, a shell vibration gyro harmonic oscillator with a multi-curved surface fusion revolving body structure needs to be invented to solve the problems of poor impact resistance, low quality factor, complex processing technology and high control cost of the existing shell vibration gyro.

Disclosure of Invention

The invention provides a shell vibration gyro harmonic oscillator with a multi-curved surface fused revolving body structure, which aims to solve the problems of poor impact resistance, low quality factor, complex processing technology and high control cost of the existing shell vibration gyro.

The invention is realized by adopting the following technical scheme:

a shell vibration gyro harmonic oscillator with a multi-curved surface fusion revolving body structure comprises a resonance mass, a supporting seat, four driving electrodes, four driving mode feedback electrodes, four detection electrodes and four detection mode compensation electrodes;

wherein the resonance mass is a circular cup-shaped structure with an upward opening; a vertically through center round hole is formed in the center of the bottom wall of the resonance mass; eight isolating round holes which are communicated up and down are formed in the edge of the bottom wall of the resonance mass, and the eight isolating round holes are symmetrically distributed around the center line of the resonance mass;

the side wall of the resonance mass comprises a lower section side wall and an upper section side wall; the side wall of the lower section is in a cone-shaped structure, and the diameter of the side wall of the lower section is gradually increased from bottom to top; the side wall of the lower section is provided with eight isolating bar holes which are communicated from inside to outside and are arranged along the direction of a bus, and the eight isolating bar holes are symmetrically distributed around the center line of the resonance mass; the center lines of the eight isolating bar holes are intersected with the center lines of the eight isolating round holes in a one-to-one correspondence manner; the side wall of the upper section is of a spherical belt structure, and the diameter of the side wall of the upper section is gradually increased from bottom to top;

the supporting seat is of a circular cup-shaped structure with a downward opening, and the supporting seat is coaxially fixed on the edge of an orifice at the upper end of the central circular hole; the center of the top wall of the supporting seat is provided with an installation screw hole which is communicated up and down;

the four driving electrodes, the four driving mode feedback electrodes, the four detection electrodes and the four detection mode compensation electrodes are all of a strip-shaped sheet structure, and the four driving electrodes, the four driving mode feedback electrodes, the four detection electrodes and the four detection mode compensation electrodes are all piezoelectric ceramic electrodes polarized along the thickness direction;

the negative electrode surfaces of the four driving electrodes and the negative electrode surfaces of the four detection mode compensation electrodes are fixed with the outer bottom wall of the resonance mass, and the four driving electrodes and the four detection mode compensation electrodes are arranged along the radial direction; the four driving electrodes and the four detection mode compensation electrodes are symmetrically distributed around the center line of the resonance mass; the four driving electrodes are correspondingly positioned between the first isolating circular hole and the second isolating circular hole, between the third isolating circular hole and the fourth isolating circular hole, between the fifth isolating circular hole and the sixth isolating circular hole and between the seventh isolating circular hole and the eighth isolating circular hole one by one; the four detection mode compensation electrodes are correspondingly positioned between the second isolation round hole and the third isolation round hole, between the fourth isolation round hole and the fifth isolation round hole, between the sixth isolation round hole and the seventh isolation round hole, and between the eighth isolation round hole and the first isolation round hole;

the negative electrode surfaces of the four driving mode feedback electrodes and the negative electrode surfaces of the four detection electrodes are fixed with the outer side wall of the lower section of the resonance mass, and the four driving mode feedback electrodes and the four detection electrodes are arranged along the direction of a bus; the four driving mode feedback electrodes and the four detection electrodes are symmetrically distributed around the center line of the resonance mass; the four driving mode feedback electrodes are correspondingly positioned between the first isolating bar hole and the second isolating bar hole, between the third isolating bar hole and the fourth isolating bar hole, between the fifth isolating bar hole and the sixth isolating bar hole, and between the seventh isolating bar hole and the eighth isolating bar hole; the four detection electrodes are correspondingly positioned between the second spacing bar hole and the third spacing bar hole, between the fourth spacing bar hole and the fifth spacing bar hole, between the sixth spacing bar hole and the seventh spacing bar hole, and between the eighth spacing bar hole and the first spacing bar hole one by one.

During operation, a mounting screw rod penetrates through the mounting screw hole, and the lower end of the mounting screw rod penetrates through the central circular hole to be fixed with the base of the shell vibrating gyroscope. The positive electrode surfaces of the four driving electrodes, the positive electrode surfaces of the four driving mode feedback electrodes, the positive electrode surfaces of the four detection mode compensation electrodes and the outer wall of the resonance mass are connected with a control system of the shell vibration gyro through metal wires.

The specific working process is as follows: firstly, a control system of the shell vibration gyro generates two paths of driving voltage signals with the same amplitude, the same frequency and the opposite phase, loads a first path of driving voltage signals to a first driving electrode and a third driving electrode, and loads a second path of driving voltage signals to a second driving electrode and a fourth driving electrode. Under the action of the inverse piezoelectric effect, the first driving electrode and the third driving electrode vibrate in the same amplitude, the same frequency and the same phase, the second driving electrode and the fourth driving electrode vibrate in the same amplitude, the same frequency and the same phase, the first driving electrode and the second driving electrode vibrate in the same amplitude, the same frequency and the opposite phase, and the third driving electrode and the fourth driving electrode vibrate in the same amplitude, the same frequency and the opposite phase. When no angular velocity is input, the present invention makes four-antinode vibration in a driving mode (as shown in fig. 3) under the driving of four driving electrodes, thereby generating a standing wave in a circumferential direction. At this time, the four detection electrodes are located at nodes of the four-antinode vibration (the four drive mode feedback electrodes are located at antinodes of the four-antinode vibration), thereby making the output of the case vibration gyro zero. Under the action of the direct piezoelectric effect, four driving mode feedback electrodes generate four feedback voltage signals in real time, a control system of the shell vibration gyro calculates the vibration frequency and the vibration amplitude of the shell vibration gyro in real time according to the four feedback voltage signals, and adjusts the two driving voltage signals in real time according to the calculation result, so that the vibration frequency and the vibration amplitude of the shell vibration gyro are kept stable, and the vibration mode of the shell vibration gyro is kept stable. When an angular velocity is input, the standing wave precesses under the action of the Coriolis force (the precession direction is related to the angular velocity direction), so that the vibration mode of the invention deflects, and the invention performs four-antinode vibration in a detection mode. At this time, the four detection electrodes are no longer located at the nodes of the four-antinode vibration (the four drive mode feedback electrodes are no longer located at the antinodes of the four-antinode vibration). Under the action of the direct piezoelectric effect, four detection electrodes generate four detection voltage signals in real time, a control system of the shell vibration gyro calculates the vibration mode deflection angle of the invention in real time according to the four detection voltage signals, generates four compensation voltage signals in real time according to the calculation result, and then loads the four compensation voltage signals to the four detection mode compensation electrodes in real time. Under the action of the inverse piezoelectric effect, the four detection mode compensation electrodes vibrate, so that the vibration mode deflection angle of the invention is kept stable. Then, the control system of the shell vibration gyro calculates the input angular velocity in real time according to the vibration mode deflection angle of the invention, thereby enabling the shell vibration gyro to measure the input angular velocity in real time. In the above process, the isolating circular holes and the isolating bar holes have the function of eliminating the disturbance between the electrodes.

Based on the above process, the shell vibration gyro harmonic oscillator with the multi-curved surface fusion revolving body structure provided by the invention has the following advantages by adopting the multi-curved surface fusion revolving body structure (the structure fuses a circular bottom wall, a conical barrel-shaped lower section side wall and a spherical strip-shaped upper section side wall): firstly, the multi-curved surface fusion revolving body structure adopted by the invention has the characteristics of easy vibration and stable vibration, thereby effectively enhancing the shock resistance of the shell vibration gyro and effectively improving the quality factor of the shell vibration gyro. Secondly, the multi-curved surface fusion revolving body structure adopted by the invention is easy to realize modular processing, thereby effectively simplifying the processing technology of the shell vibration gyro. Thirdly, the invention does not work based on the traditional static control mode, but works based on a brand-new piezoelectric control mode, thereby effectively reducing the control cost of the shell vibration gyro.

The invention has reasonable structure and ingenious design, effectively solves the problems of poor shock resistance, low quality factor, complex processing technology and high control cost of the existing shell vibration gyro, and is suitable for the fields of aviation, aerospace, navigation, industry, agriculture, traffic and the like.

Drawings

Fig. 1 is a schematic perspective view of the present invention.

Fig. 2 is a schematic perspective view of the present invention.

Fig. 3 is a schematic view of the mode shape of the present invention in a driving mode.

Fig. 4 is a schematic view of the mode shape of the present invention in the detection mode.

In the figure: 1-resonance mass, 2-support base, 3-drive electrode, 4-drive mode feedback electrode, 5-detection electrode, 6-detection mode compensation electrode, 7-central circular hole, 8-isolation circular hole, 9-isolation bar hole and 10-installation screw hole.

Detailed Description

A shell vibration gyro harmonic oscillator with a multi-curved surface fusion revolving body structure comprises a resonance mass 1, a supporting seat 2, four driving electrodes 3, four driving mode feedback electrodes 4, four detection electrodes 5 and four detection mode compensation electrodes 6;

wherein, the resonance mass 1 is a round cup-shaped structure with an upward opening; a central circular hole 7 which is vertically communicated is formed in the center of the bottom wall of the resonance mass 1; eight isolating round holes 8 which are communicated up and down are formed in the edge of the bottom wall of the resonant mass 1, and the eight isolating round holes 8 are symmetrically distributed around the center line of the resonant mass 1;

the side wall of the resonance mass 1 comprises a lower section side wall and an upper section side wall; the side wall of the lower section is in a cone-shaped structure, and the diameter of the side wall of the lower section is gradually increased from bottom to top; the side wall of the lower section is provided with eight isolating bar holes 9 which are communicated from inside to outside and are arranged along the bus direction, and the eight isolating bar holes 9 are symmetrically distributed around the center line of the resonance mass 1; the central lines of the eight isolating bar holes 9 are intersected with the central lines of the eight isolating round holes 8 in a one-to-one correspondence manner; the side wall of the upper section is of a spherical belt structure, and the diameter of the side wall of the upper section is gradually increased from bottom to top;

the supporting seat 2 is of a circular cup-shaped structure with a downward opening, and the supporting seat 2 is coaxially fixed on the edge of an orifice at the upper end of the central circular hole 7; the center of the top wall of the supporting seat 2 is provided with an installation screw hole 10 which is communicated up and down;

the four driving electrodes 3, the four driving mode feedback electrodes 4, the four detection electrodes 5 and the four detection mode compensation electrodes 6 are all of a long strip-shaped sheet structure, and the four driving electrodes 3, the four driving mode feedback electrodes 4, the four detection electrodes 5 and the four detection mode compensation electrodes 6 are all piezoelectric ceramic electrodes polarized along the thickness direction;

the negative electrode surfaces of the four driving electrodes 3 and the negative electrode surfaces of the four detection mode compensation electrodes 6 are all fixed with the outer bottom wall of the resonance mass 1, and the four driving electrodes 3 and the four detection mode compensation electrodes 6 are all arranged along the radial direction; the four drive electrodes 3 and the four detection mode compensation electrodes 6 are symmetrically distributed around the center line of the resonant mass 1; the four driving electrodes 3 are correspondingly positioned between the first isolating circular hole 8 and the second isolating circular hole 8, between the third isolating circular hole 8 and the fourth isolating circular hole 8, between the fifth isolating circular hole 8 and the sixth isolating circular hole 8, and between the seventh isolating circular hole 8 and the eighth isolating circular hole 8; the four detection mode compensation electrodes 6 are correspondingly positioned between the second isolation circular hole 8 and the third isolation circular hole 8, between the fourth isolation circular hole 8 and the fifth isolation circular hole 8, between the sixth isolation circular hole 8 and the seventh isolation circular hole 8, and between the eighth isolation circular hole 8 and the first isolation circular hole 8;

the negative electrode surfaces of the four driving mode feedback electrodes 4 and the negative electrode surfaces of the four detection electrodes 5 are fixed with the outer side wall of the lower section of the resonance mass 1, and the four driving mode feedback electrodes 4 and the four detection electrodes 5 are arranged along the direction of a bus; four drive mode feedback electrodes 4 and four detection electrodes 5 are symmetrically distributed around the center line of the resonance mass 1; the four driving mode feedback electrodes 4 are correspondingly positioned between the first isolating bar hole 9 and the second isolating bar hole 9, between the third isolating bar hole 9 and the fourth isolating bar hole 9, between the fifth isolating bar hole 9 and the sixth isolating bar hole 9, and between the seventh isolating bar hole 9 and the eighth isolating bar hole 9; the four detection electrodes 5 are located between the second spacer bar hole 9 and the third spacer bar hole 9, between the fourth spacer bar hole 9 and the fifth spacer bar hole 9, between the sixth spacer bar hole 9 and the seventh spacer bar hole 9, and between the eighth spacer bar hole 9 and the first spacer bar hole 9 in one-to-one correspondence.

The resonance mass 1 and the supporting seat 2 are both made of Ni-Span-C Alloy 902 constant elasticity Alloy.

The piezoelectric ceramic is PZT-5H piezoelectric ceramic.

The negative electrode surfaces of the four driving electrodes 3 and the negative electrode surfaces of the four detection mode compensation electrodes 6 are fixed with the outer bottom wall of the resonance mass 1 through conductive adhesive; the negative electrode surfaces of the four driving mode feedback electrodes 4 and the negative electrode surfaces of the four detection electrodes 5 are fixed with the outer side wall of the lower section of the resonance mass 1 through conductive adhesive.

The thickness of the bottom wall of the resonant mass 1 is 0.8 mm; the thickness of the lower section side wall of the resonance mass 1 is 1mm, and the length of a bus is 10 mm; the thickness of the upper section side wall of the resonance mass 1 is 1.2mm, the height is 7.5mm, and the outer diameter is 30 mm; the thickness of the supporting seat 2 is 0.5mm, and the height is 4.2 mm; the four driving electrodes 3 and the four detection mode compensation electrodes 6 are 5.6mm in length, 1.6mm in width and 0.2mm in thickness; the four driving mode feedback electrodes 4 and the four detection electrodes 5 are 9mm in length, 1.6mm in width and 0.2mm in thickness; the diameter of the central circular hole 7 is 4 mm; the diameters of the eight isolating circular holes 8 are all 2 mm; the hole distances between the eight isolating circular holes 8 and the central circular hole 7 are all 5 mm; the eight isolating bar holes 9 are 9mm in length and 2mm in width; the diameter of the mounting screw hole 10 is 2 mm.

The first-order natural frequency of the resonant mass 1 is 1516.7Hz, the second-order natural frequency is 1531.6Hz, the third-order natural frequency is 4385.2Hz, the fourth-order natural frequency is 4385.4Hz, the fifth-order natural frequency is 5305.2Hz, the sixth-order natural frequency is 5425Hz, the seventh-order natural frequency is 11813Hz, the eighth-order natural frequency is 11814Hz, the driving modal frequency is 4385.4Hz, and the detection modal frequency is 4385.2 Hz.

While specific embodiments of the invention have been described above, it will be appreciated by those skilled in the art that these are by way of example only, and that the scope of the invention is defined by the appended claims. Various changes and modifications to these embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention, and these changes and modifications are within the scope of the invention.