Low noise timing belt

Abstract: Low noise timing belts for use in belt drive systems include either perforations (46, 47, 48) cut into their thin segments (43) or helical grooves cut into their thick segments in order to allow air pockets to escape in all directions during teeth engagement of belts and pulleys, thereby reducing the noise generated in the process.

Description: This invention relates to timing belt systems, and more particularly, to low noise timing belts for use in such systems. Excessive noise from copier/printers in working environments has been an irritant to users from the advent of such machines until the present day. One of the major contributors to machine noise has been found to be timing belts where engagement between the teeth of the belts and the pulleys emit noise. As the air pockets between the teeth of the belts and the pulleys are displaced periodically along the lateral direction of motion, the disturbance modulates air in the surrounding areas and generates noise. Noise spectra of a typical timing belt as shown in FIG. 1 indicate that the acoustic energy comes from two areas; (i) the energy at mesh frequency and its harmonics; and (ii) the energy at high frequencies which is a result of impact. The noise level is proportional to a number of things, for example, the volume of the air pockets being displaced and the rate at which they are displaced. The peaks at 630 Hz and 1250 Hz in FIG. 1 are the mesh frequency and the harmonics, respectively. The energy at 2 KHz and above is due to impact of the teeth of the timing belt. Treatment of flat belts for various reasons includes: U.S. Patent No. 1,661,300 discloses a transmission belt that allows a film of air that is caught between a moving belt and a pulley of a transmission system to escape immediately upon being trapped, thereby avoiding slipping and enabling the belt to transmit power under less tension. The belt consists of perforations (S, 8) on one side of the belt which connect to longitudinal grooves (4, 10) cut into the other side of the belt. The openings free the trapped air that accumulates between the belt and its pulley. U.S. Patent No. 383,373 is directed to a belt apparatus which prevents the air cushioning of belting upon the face of a pulley. The belt is perforated to provide air spaces in the solid belting through which a layer of air may escape. U.S. Patent No. 4,832,672 discloses a precompaction belt used in the production of particle boards which has predetermined perforations to allow hot air from a hot press to escape. In addition, the perforated belt avoids further difficulties such as the adherence or scattering of particles by means of these holes. U.S. Patent No. 249,897 is directed to a belt and pulley apparatus consisting of holes and grooves along their surfaces to afford free escape of air. This design allows the belt and the pulley to have an increased frictional contact facilitated by the removal of the thin film of air that can develop between them. U.S. Patent No. 1,028,783 discloses a motor cycle driving belt which employs several different configurations to allow air and rainwater to escape from between the driving belts and the grooved pulleys they interact with. The grooves and studs provide the belt with greater flexibility and thus, more resiliency. U.S. Patent No. 455,852 is directed to a belt having transverse channels on its face which facilitate the dissipation of a layer of air which is confined between a pulley and belt faces. The channels, through which the air is forced, are at right angles to the length of the belt. U.S. Patent No. 137,224 discloses a feed and delivery apron for machines used in the preparation of fiber made of rubber and cloth upon which grooves and projections are formed which increase the flexibility of the belt. Page 9 of the January 24, 1991 issue of Machine Design discloses a timing belt by Berg, Inc. of East Rockaway, N.Y. 11518, that lists being silent as a feature. EP-A-0,211,730 describes a toothed belt and pulley transmission system in which the belts are perforated to allow the escape of air and hence reduce noise. It is an object of the present invention to reduce the noise level of a toothed belt and pulley system. According to the present invention, there is provided a belt drive system that includes a timing belt entrained around spaced apart, toothed, drive and driven members, the timing belt comprising alternating teeth and lands on one surface thereof, characterised in that said teeth, or said teeth and said lands, include randomly patterned grooves therein extending generally transversely of the teeth, that allow air to escape when said timing belt teeth mate with teeth of the drive and driven members during operation of the system, thereby reducing system noise. It has been found at present through research that if the air pockets between the teeth of belts and pulleys are allowed to escape in all directions, the acoustic energy at mesh frequency, as well as the harmonics, will be minimized. The noise level due to impact will also be reduced. Accordingly, a low noise timing belt is disclosed in which grooves are cut across the teeth of the belt in order to allow air to escape in all directions upon impact of the teeth of the timing belt with the pulley on which it is mounted and reduce noise in the process. A timing belt system in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- FIG. 1 is a typical noise spectrum of a prior art timing belt. FIG. 2A shows a partial, enlarged plan view of a timing belt in accordance with the present invention that includes helical grooves through the peaks of the belt. FIG. 2B is a partial enlarged elevational view of the timing belt of FIG. 2A showing the profile of the belt. FIG. 2C is a partial, enlarged plan view of a timing belt in accordance with the present invention that includes transverse grooves across the teeth and lands of the belt. FIG. 3 is a graph showing test results obtained by comparing the noise levels of the timing belt of FIG. 2A against a conventional timing belt. If air in pockets between the teeth of belts and pulleys is allowed to escape in all directions, the acoustic energy at the mesh frequency and harmonics will be minimized. A preferred means of accomplishing this is shown in FIGS. 2A and 2B that comprises a timing belt member 10 that includes a main belt portion 11 that has a series or plurality of peaks or orthogonal ridges or teeth 13 thereon that are each followed by a land or valley 12 thereof. The teeth 13 have randomly patterned, helical shaped grooves 18, cut therethrough to the land portions of the belt 11. With this helical shaped pattern or configuration of grooves in the belt, noise is allowed to escape in all directions when the teeth of the belt come into contact with teeth of pulleys. With 5 mm HTD belts, test results as depicted in FIG. 3 show noise improvement of 6 dBA (75%). The spirals 18 will not weaken the belts or affect the reliability of drive systems since most timing belts include a high safety factor as a design parameter. The results of FIG. 3 were obtained with a center distance (axial distance between pulleys) of 220 mm, a tension of 135N and a torque of 0.3 Nm. IN FIG. 3, the noise level in dBA is plotted vis-a-vis the speed of a timing belt in M/S. The symbol  is used to designate a conventional timing belt while the symbol □ is used to designate the test results of the timing belt of FIG. 2A. Grooves of any configuration can be used to yield similar results as long as they are transverse to the longitudinal dimension of the belt. An alternative embodiment of a low noise timing belt is shown in FIG. 2C that comprises a belt 30 that has a main belt portion 31 with a plurality of teeth 35 projecting orthogonally thereto. The teeth 35 are spaced a predetermined distance apart from each other by land portions 33. In order to minimize noise created by the teeth of the timing belt meshing with teeth of pulleys on which the belt is mounted, a transverse, random pattern of grooves 36 are cut into the teeth and lands that allow air to escape in all directions as the teeth of the belt and pulleys mesh during operation of a timing belt system. Grooves 36 do not extend completely through the lands 33. As will be readily understood from the foregoing description, the low noise feature of the timing belt of the present invention is attained by providing grooves across the teeth of the timing belt. The invention has been described in detail with particular reference to the preferred embodiment thereof, but it will be understood that reasonable variations and modifications are possible without departing from the scope of the invention. For example, the belt may include both grooves and perforations.

Claims: A belt drive system that includes a timing belt entrained around spaced apart, toothed, drive and driven members, the timing belt comprising alternating teeth (13) and lands (12) on one surface thereof, characterised in that said teeth, or said teeth and said lands, include randomly patterned grooves (18, 36) therein extending generally transversely of the teeth, that allow air to escape when said timing belt teeth mate with teeth of the drive and driven members during operation of the system, thereby reducing system noise. The belt drive system of claim 1, wherein said grooves (18, 36) extend in helical fashion around the belt. The belt drive system of claim 1 or claim 2, wherein said grooves (36) are randomly spaced with respect to each other.

Inventors: SANBORN WALTER J, WONG CHEE-CHIU JOSEPH, SANBORN, WALTER J., WONG, CHEE-CHIU JOSEPH
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1992
Main classification: F16H7
IPC codes: F16G1, B41J23, G03G21, F16H7, G03G15