Inertia force generating device

Abstract: An inertia force generating device comprises two pairs of coaxial counter-rotating eccentric rotors (12, 14, 16 and 18), whose rotational speeds and relative positions are automatically and continuously controlled so as to cancel undesirable vibrations produced by another device. within each rotor pair, the two rotors have an adjustable angle between their mass centers, so that the effective ecentricity of the pair can be varied, and the phase between the two pairs can also be changed, to alter the direction of the maximum or minimum inertial forces developed. The four rotors include shells (52, 54, 56 and 58) of different diameter, nested together on a center plane of the device.

Description: Background of the Invention This invention relates to the field of vibration control, and particularly to an active inertial force generator capable of developing periodic forces of controllable frequency, amplitude, direction and phase, for cancelling undesirable vibrations developed by aircraft engines or the like. For controlling the generation or transmission of vibrations developed by machinery, various schemes and mechanisms are well known. These fall generally into categories of (1) passive vibration dampers, such as flywheel dampers, (2) vibration isolators, such as shock mounts, (3) hydraulic vibrators for generating periodic forces to counteract undesirable vibrations, and (4) mechanical active vibration compensators. The present invention is in the last group. Within that group, there are prior disclosures of devices which are either reciprocating or rotary. U.S. Patent 3,208,292, for example, discloses a variable force oscillator comprising four imbalanced flywheels arranged in counter-rotating pairs on two parallel axes; a differential gear arrangement permits one to change the angle between the eccentrically weighted portions, and thus change the magnitude of the vibration developed. U.S. Patents No. 3,209,525, No. 4,289,042 and No. 4,667,532 show arrangements with two or three eccentric weights. With none of these devices, however, can one simultaneously control the frequency, magnitude and direction of the generated forces, or correct the phase between another source of vibration and the device. U.S. Patent 4,688,355 does show an automatic balancer of the hydraulic type for grinding machines, but it requires a stationary fixture for hydraulic pressure to act against, and is not capable of developing an inertial force for compensating or cancelling vibrations developed by another device. U.S. Patent No. 4,084,445 discloses an inertial force generating device having a stationary housing, first and second pairs of eccentrically weighted rotors disposed within the housing for rotation about an axis common to all the rotors, means for rotating the pairs in opposite directions and means for adjusting the phase angle between the rotor pairs so as to control the direction of the cancelling force generated by the device. However, the weights within each pair are fixed to rotate together so that each pair has a fixed eccentricity. With such a device, the magnitude of the cancelling force is fixed and also the shape of the wave form produced by the cancelling device is invariable. None of the prior devices is capable of simultaneously altering the magnitude, frequency, phase, and direction of its vibrational forces while in operation. In short, the problem of producing compensating periodic forces of readily changeable frequency, magnitude, direction and phase is a problem only partially addressed by the prior art, and was never heretofore solved. In view of the foregoing, it is an object of this invention to generate periodic inertial forces for cancelling engine vibrations and the like, which may have varying frequency, magnitude and direction. Another object is to provide a system for maintaining proper phase between the cancelling forces and the undesired vibration. A further object is to provide a rotary mechanical vibration canceller with plural rotors nested in a common plane, so as to produce force vectors only in that plane. Yet another object is to control a vibration cancelling device automatically in response to sensed vibrations in the environment of the device, so as to match the inertial forces of the device to those of the environment. Summary of the Invention According to the present invention there is provided an inertial force generating device for producing forces to cancel undesired vibrations of the type having a stationary housing, first, second, third and fourth eccentrically weighted rotors disposed within the housing having imbalanced portions for rotation about an axis which is common to all said rotors, said first and second rotors comprising a first rotor pair and said third and fourth rotors comprising a second rotor pair, means for rotating the first rotor pair in one direction and the second rotor pair in the opposite direction and means for adjusting the angular position of the first rotor pair relative to the angular position of the second rotor pair, characterised by: first means for adjusting the angular position of the first rotor relative to the second rotor during operation of said device so as to vary the effective eccentricity produced by said first rotor pair; and second means for adjusting the angular position of the third rotor relative to the fourth rotor during operation of said device so as to vary the effective eccentricity produced by said second rotor pair; whereby the angular positions of all of said rotors relative to one another is adjustable during operation of said device. According to the present invention there is also provided a method of cancelling an undesired periodic vibration of determinable magnitude, frequency and direction, comprising the steps of providing a force cancelling device with four rotatable eccentrically weighted rotors, each rotor having an eccentric center of mass; rotating said rotors about a common axis in synchronization with one another, with two of said rotors comprising one pair rotating in one direction and the other two of said rotors comprising another pair rotating in the other direction, controlling the speed of rotation of said rotors as a function of the frequency of the undesired vibration, and adjusting the phase angle between the two rotor pairs so as to control the direction of the cancelling force generated by the device as a function of the direction of the undesired vibration, characterised by: providing all four rotors so that said rotors are rotatable independently of one another; adjusting the angle between the mass centers of the two rotors in each pair while said rotors are rotating so as to control the amplitude of the inertial force generated by the device as a function of the magnitude of the undesired vibration; and adjusting the phase of the device with respect to that of the undesired vibration while said rotors are rotating; so as to oppose and cancel said vibration. In an alternative configuration, the imbalanced portions are in the form of parallel plates, placed side by side along the axis of rotation and as close as possible to one another and perpendicular to the axis of rotation. Brief Description of the Drawings In the accompanying drawings, Fig. 1a is a sectional view of a device embodying the invention, taken along diametral plane thereof; Fig 1b is an alternative embodiment thereof; Fig. 2 is an exploded perspective view of the device shown in Fig. 1a, with the casing the other parts omitted for clarity; Fig. 3a is a diagram showing major components of a system for controlling the device, when mounted on an engine so as to cancel vibrations generated by the engine; Fig. 3b is an alternative embodiment thereof; and Fig. 4 is a view corresponding to Fig 1a, of a second alternative embodiment. Detailed Description of the Preferred Embodiment The invention is embodied in an inertial force generating device shown in the drawings. With reference to Fig. 1a, the device comprises a housing (10) containing two pairs of rotors (12, 14) and (16, 18) mounted concentrically around a common shaft (20) for rotation thereabout. Each of the inner rotors is supported upon the shaft (20) by an inner pair of anti-friction bearings; in Fig. 1a, the left pair of inner bearings supporting the rotor (12) are identified by numerals (32, 34), and the right pair (36, 38) support the rotor (16). The two outer rotors (14, 18) are supported by respective outer pairs of anti-friction bearings, the left pair being designated by (42, 44) and the right pair by (46, 48). Each rotor comprises a drive sleeve of a first diameter integrally connected by an annular shoulder to a shell of a somewhat greater diameter. The four shells, designated (52, 54, 56 and 58) in Fig. 1a, are of sufficiently different diameters that the shells nest within one another around a common plane perpendicular to, and bisecting, the longitudinal axis of the device. The outer diameter of one shell is less than the inner diameter of the shell around it, leaving an air gap so that none of the shells contacts its neighbor. Thus, there is no mechanical connection between the shells. A segment of each shell is cut away, leaving eccentric portions (60) of the shell (Fig. 2) which provide the desired eccentricity. The dimensions of the shells (diameter and thickness) and of the eccentric portions (segment angle and length) are chosen so that the mass eccentricity of the shells is identical, despite their different diameters. By "mass eccentricity" is meant the mass of the shell multiplied by the radial distance of its center of mass from the rotational axis. The centers of mass, one of which is shown, designated by reference letter M in Fig. 2, lie on or near a common plane perpendicular to the common axis of the rotors, so that the effective net inertial forces they produce are substantially within that plane. Referring again to Fig. 1a, an annular, variable speed drive motor is connected to each of the rotors; the motors are designated (62, 64, 66, 68) for the rotors (12, 14, 16, 18) respectively. Each motor has a stationary portion connected to a stationary portion (either the housing (10) or the shaft (20)) of the device, and a movable portion connected to the respective rotor. Fig. 1b shows an alternative embodiment of the device, which differs from that of Fig. 1a primarily in the arrangement of bearings supporting the outer rotors. Parts identical to those of Fig. 1a are indicated by identical reference numerals, and counterpart, non-identical components are designated by reference numerals differing from those of Fig. 1a by a hundred. The two outer rotors (114, 118) are supported by respective outer pairs of anti-friction bearings, the left pair being designated (142, 144) and the right pair by (146, 148). As the arrangement of rotors and the function of the embodiments are identical, Fig. 1a is not discussed further. With reference to Fig. 2, each rotor is provided with circumferentially spaced markings or magnets (generically "triggers" in the claims that follow) (70) on its outer surface, in the vicinity of means for detecting passage thereof to develop signals from which the speed and angular position of the particular rotor can be inferred. The sensors, designated (72, 74, 76, 78) in Fig. 1, may be optical or magnetic and are mounted in apertures in the housing. Fig. 3a depicts the inertial force generating device (10) mounted upon an engine (80) that may produce objectionable vibrations of varying frequency, magnitude, and direction. An accelerometer (82) is mounted either on the device (10) on the engine in the vicinity of the device, or on the structure remote from the device. When two accelerometers are utilised, they are typically, but not necessarily, mounted in the force plane, and mutually orthogonal. Alternate sensor schemes might include geophones or microphones, depending on the application. Output from the accelerometer is directed to an FFT program module (84) which takes the time domain vibration information and converts it into the frequency domain. The program prepares the information for the excitation evaluation program (86) which takes the frequency domain information from the FFT program and deletes the effect of the force canceller, then applies evaluation criteria to the results to determine which vibration to eliminate. The output of the program (86) is filtered by an adjustable frequency filter (88) providing a clear signal for phasing and mass-eccentricity adjustment by the computer update program (90) that calculates the mass eccentricity and frequency required to cancel the undesired vibration. Data from program (90) is stored in memory (92); stored values may be accessed by the computer (86). Program module (94) receives signals both from the module (90) and from a module (96) which verifies frequency, offset angle 0 and phase information from the sensors (72, 74, 76, 78) of the device (10). The module (90) then generates motor drive signals as necessary to change the frequency (speed), offset angle 0 and phase (with respect to the engine) of the device (10). A simplified form of the automatic control system is shown in Fig. 3b, where similar computer program modules are provided, except that the items (84, 86, 88) of Fig. 3a are replaced by a single module (175). The simplified arrangement is otherwise identical to that described above, and performs the same function; i.e., that of matching the frequency, amplitude, direction, and phase of the generated vibrational force to that of the engine (80). In operation, the computer (94), in conjunction with a power supply, provides power to the four motors of the device, driving the rotors to a desired, synchronised speed in relation to that of the engine, generally equal to the engine speed or an integral fraction thereof. The left pair (12, 14) of rotors are rotated in one direction, and the right pair are turned in the opposite direction, at the same speed. In Fig. 2, the inertial force vector generated by each rotor shell is designated F with a subscript corresponding to the particular shell; the inertial forces of the individual eccentrics produce a net effective force F e whose magnitude and direction depends upon the magnitude and angular offset angle 0 between the individual forces. When angle 0 equals 180°, the mass centers of the two rotors are opposed, and thus the effective eccentricity of the pair is zero, while when they are aligned (0 equals 0°), the mass eccentricity is at a maximum. Thus, by varying the angular offset angle 0 between the center of mass radii, the magnitude of the inertial force generated by the paired rotors can be controlled. The offset angles of the two pairs could be independently controlled at different values; when the offsets of both pairs are kept substantially identical, purely reciprocating sinusoidal net forces result. When the offsets of both pairs are different, an eccentric force that changes magnitude with angular orientation is generated. The direction of the generated peak inertial force is controlled by controlling the phase difference between the two rotor pairs. As the rotor pairs rotate within the housing, their effective mass centers are aligned at two opposed points during each revolution. At the points where the effective mass centers of the oppositely rotating first and second rotor pairs are in alignment, the inertial force of the combination is the greatest; it is minimum or zero where the mass centers are 180° opposed, substantially as shown in Fig. 2. By controlling the phase relationship between the right and left rotor pairs, the angular position of the alignment point with respect to the stationary housing can be set; as a consequence, the orientation of the generated minimum and maximum net force vector can be changed at will. In order for the device described above to accomplish the objective of cancelling vibrations developed by the engine upon which it is mounted, the phase between the rotors and the engine is automatically adjusted, by the control system, so that the peaks of the inertial forces generated by the device are in proper phase with (opposing) those of the engine. The frequency of the developed inertial force is altered by changing the speed of the rotors. Therefore, the frequency, amplitude and direction of the developed maximum and minimum inertial forces, in addition to their phase with respect to that of its environment, are continuously controllable as the device operates. Fig. 4 shows another alternative embodiment of the invention, wherein the rotors, instead of being in the form of nested shells (which enables all eccentric mass centers to lie in a common plane) are instead parallel eccentric plates (252, 254, 256 and 258), the plates being as thin and as close together as possible so as to produce forces nearly within a common plane. The goal of obtaining resultant forces in a common plane is approximately met with this embodiment. It should be understood that the described use of the subject device, on an engine, is only illustrative, and that the device may be used in any environment where there is a periodic, monitorable, vibration of frequency and magnitude within the range of magnitudes and frequencies achievable by the device. To modify the device described above, in order to adapt to particular frequency and magnitude ranges, is considered within the skill of the artisan, as are details of the control systems illustrated in Figs. 3a and 3b. Although two pairs of rotors are preferred for carrying out the invention, even multiples of four could be used as well. Inasmuch as the invention is subject to these and other variations, it is intended that the foregoing description shall be interpreted only as illustrative of the invention described by the following claims.

Claims: An inertial force generating device for producing forces to cancel undesired vibrations of the type having a stationary housing (10), first (12), second (14), third (16) and fourth (18) eccentrically weighted rotors disposed within the housing (10) having imbalanced portions for rotation about an axis which is common to all said rotors, said first (12) and second (14) rotors comprising a first rotor pair (12, 14) and said third (16) and fourth (18) rotors comprising a second rotor pair (16, 18), means (62, 64, 66, 68) for rotating the first rotor pair (12, 14) in one direction and the second rotor pair (16, 18) in the opposite direction and means (62, 64, 66, 68, 72, 74, 76, 78, 82-92) for adjusting the angular position of the first rotor pair (12, 14) relative to the angular position of the second rotor pair (16, 18), characterised by: first means (62, 64, 72, 74, 82-96) for adjusting the angular position of the first rotor (12) relative to the second rotor (14) during operation of said device so as to vary the effective eccentricity produced by said first rotor pair (12, 14); and second means (66, 68, 76, 78, 82-96) for adjusting the angular position of the third rotor (16) relative to the fourth rotor (18) during operation of said device so as to vary the effective eccentricity produced by said second rotor pair (16, 18); whereby the angular positions of all of said rotors (12, 14, 16, 18) relative to one another is adjustable during operation of said device. A device as claimed in claim 1, wherein said imbalanced portions (60) are nested radially, so as to develop force vectors in a common plane perpendicular to said axis; and further comprising means (62, 64, 66, 68, 72, 74, 76, 78, 82-96) for adjusting the phase angle between the rotor pairs so as to control the direction of the cancelling force generated by the device. A device as claimed in claim 1 or 2, wherein all of said rotors (12, 14, 16, 18) have substantially identical mass eccentricity. A device as claimed in claim 3, wherein each of said imbalanced portions (60) comprises an unbalanced shell, said shells (52, 54, 56, 58) being concentric and out of contact with one another, so as to be independently rotatable. A device as claimed in claim 4, wherein the rotating means comprise plural motors (62, 64, 66, 68), each motor being connected to a respective one of said rotors (12, 14, 16, 18). A device as claimed in claim 5, wherein all of said motors (62, 64, 66, 68) rotate said rotors (12, 14, 16, 18) at the same absolute speed. A device as claimed in claim 6, wherein each of said shells (52, 54, 56, 58) has a primary plane in which its center of mass lies, and further comprising means (62, 64, 66, 68, 72, 74, 76, 78, 82-96) for varying the angular offset between the primary planes of the rotors (12, 14, 16, 18) within each of said pairs. A device as claimed in claim 6, wherein the means (62, 64, 66, 68, 72, 74, 76, 78, 82-96) for controlling the angle between the mass centers of the rotors (12, 14, 16, 18) within each rotor pair (12, 14; 16, 18) maintains a different offset in each rotor pair for the generation of eccentric forces of constantly varying magnitude. A device as claimed in claim 1 or 2, further comprising a shaft (20) supported within said housing (10) and extending along said common axis, each of said rotors pairs (12, 14; 16, 18) comprising an inner (12; 16) and an outer (14; 18) rotor, the inner (12; 16) rotor of each pair (12, 14; 16, 18) being supported by bearing (32; 38) on the shaft, and the outer rotor (14; 18) of each pair (12, 14; 16, 18) being supported by bearings (64; 68) on said housing (10). A device as claimed in claim 9, wherein the means (62, 64, 66, 68, 72, 74, 76, 78, 82-96) for controlling the angle between the mass centers of the rotors within each rotor pair (12, 14; 16, 18) maintains substantially identical angular offsets in both rotor pairs. A device as claimed in anyone of claims 1 to 10, further comprising an accelerometer (82) for measuring magnitude, direction and frequency of the undesired vibrations. A device as claimed in claim 11, further comprising two pairs of sensors (72, 74; 76, 78) mounted upon the housing (10), one sensor (72, 74, 76, 78) for each of said rotors (52, 54, 56, 58), for sensing circumferentially spaced markings (70) on said rotors (52, 54, 56, 58); means (96) responsive to said sensors for determining the angular speed and position of each of said rotors (52, 54, 56, 58); and means (94) responsive to both said determining means (96) and said accelerometer (82), for controlling said rotating means (10), said controlling means (94) comprising means for adjusting the speed, offset and phase of the rotors so as to cancel the undesired vibrations. A device as claimed in any one of claims 1 to 12, further comprising means (62, 64, 66, 68, 72 74, 76, 78, 82-96) for varying a point alignment of the effective centers of mass of the two rotor pairs (12, 14; 16, 18). A device as claimed in claim 1, wherein the rotors comprise closely adjacent respective plates (254, 252, 256, 258) each perpendicular to said axis, so as to develop force vectors nearly within a central plane perpendicular to said axis. A device as claimed in claim 14, further comprising means (62, 64, 66, 68, 72, 74, 76, 78, 82-96) for adjusting the phase of the device with respect to that of the undesired vibration, so as to oppose and cancel the vibration. A method of cancelling an undesired periodic vibration of determinable magnitude, frequency and direction, comprising the steps of providing a force cancelling device with four rotatable eccentrically weighted rotors (12, 14, 16, 18), each rotor (12, 14, 16, 18) having an eccentric center of mass; rotating said rotors (12, 14, 16, 18) about a common axis in synchronization with one another, with two of said rotors (12, 14) comprising one pair rotating in one direction and the other two of said rotors (16, 18) comprising another pair rotating in the other direction, controlling the speed of rotation of said rotors (12, 14, 16, 18) as a function of the frequency of the undesired vibration, and adjusting the phase angle between the two rotor pairs so as to control the direction of the cancelling force generated by the device as a function of the direction of the undesired vibration, characterised by: providing all four rotors (12, 14, 16, 18) so that said rotors are rotatable independently of one another; adjusting the angle between the mass centers of the two rotors (12, 14; 16, 18) in each pair while said rotors are rotating so as to control the amplitude of the inertial force generated by the device as a function of the magnitude of the undesired vibration; and adjusting the phase of the device with respect to that of the undesired vibration while said rotors (12, 14; 16, 18) are rotating; so as to oppose and cancel said vibration.

Inventors: JENSON WILLIAM S, NG DAVID, JENSON, WILLIAM S., NG, DAVID
Applicants: WRIGHT BARRY CORP, BARRY WRIGHT CORPORATION
Application year: 1990
Main classification: F16F15
IPC codes: B06B1, F16F15, G01H17, G10K11, G05D19