Shutter clutch

A clutch assembly for a UV module shutter, comprises a shutter shaft, a shutter drive arm, a clutch plate, at least one ball, a clutch thrust washer, and a spring assembly. The shutter shaft has a flange, the flange having a plurality of radially positioned flange detents. The shutter drive arm includes a drive pin, a drive arm cavity, and a receiver slot opening into the drive arm cavity, the drive pin disposable in a drive slot of a shutter end cap. The clutch plate may be disposed in the clutch plate cavity, may have a tab disposed in the receiver slot and a plurality of clutch plate detents. Each of the ball(s) may extend from one of the flange detents and may be partially disposable in one of the clutch plate detents. The spring assembly may exert a bias against the clutch plate and the thrust washer. The shutter shaft may extend through the shutter drive arm, the clutch plate, and the clutch thrust washer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to printing presses and, in particular, this invention relates to clutch systems for UV modules used in printing presses.

2. Background of the Invention

Ultraviolet-sensitive ink is used widely in the printing industry. One reason for its use is that ultraviolet-sensitive ink can be quickly cured by being irradiated with ultraviolet light. Such irradiation is accomplished by directing a light beam, containing high proportions of ultraviolet light, at the printed substrate.

Lamps used to generate light for this purpose also generate considerable amounts of other energy in the form of heat. This heat is usually of little consequence when a printing press is operating, because the light and heat are directed toward the substrate which is in motion during the printing process. However, if the heat and light generated by the lamp is directed at a nonmoving substrate for a sufficient amount of time, the substrate is damaged, often to the point of the ignition. Additionally, other nonmoving components of the printing press may be damaged by the high amount of heat generated from the lamps. When the printing press operation must be halted, for example to clear obstructions or replenish ink supplies, the light generated by the lamp must be prevented from impinging the substrate. One way to prevent irradiating nonmoving substrate is to power down the lamp. However, considerable time is necessary for the lamp to generate sufficient irradiation to cure the ultraviolet-sensitive ink when power is restored. Consequently, preventing irradiation from impinging nonmoving substrate when a printing press is halted has been accomplished by housing the lamp in a structure having shutters, which can be opened to allow irradiation or closed to prevent irradiation from leaving the structure.

As stated above, intense heat is generated by the UV lamp during operation. These high-energy lamps require high-voltage and fairly high current, some requiring 3000 volts and 17 amps and may generate temperatures of 1000 degrees Fahrenheit during operation. Consequently, the structures housing these high-energy lamps are subjected to periods of the extremely high temperatures. These high temperatures inescapably cause the metal components of these structures to expand and warp. One consequence of this expansion and warpage is failure of these structures to properly operate.

UV module shutter assemblies of the prior art were usually a “rigid” rotary mount design, which did not allow for expansion or warpage of the pair of aluminum shutter extrusions. Since these shutters expand, band, and warp various magnitudes, the prior art rigid mounting arrangement caused the shutter drive train gear assembly to be forced out of alignment. This misalignment resulted in premature gear wear, coolant leakage, and shutter drive train binding. A bound shutter drive often left the shutters substantially locked into a position other than that desired. Moreover, any amount of coolant leakage, no matter how small, led to a myriad of problems such as electrical shorting and fires. Development of a shutter end cap with the specific seal and bearing arrangement working in conjunction with the instant clutch and rounded drive pin significantly reduced these leakages, wear, and binding problems.

Additionally, drive trains for UV module shutters of the prior art often require extensive adjustment during manufacture and maintenance so that breakpoint torques will be at desired levels. This extensive adjustment is time consuming and often results in improperly adjusted clutches due to the complexity of design.

Accordingly, there is then a need for a shutter clutch which will not bind and which does not require extensive adjustment during manufacture and maintenance.

SUMMARY OF THE INVENTION

One feature of one embodiment of the clutch of this invention is that it is ambidextrous, i.e., fitting either shutter. Another feature of an embodiment of the instant clutch is that it will function at a predetermined breakpoint torque whether driven internally by the shutter shaft or manually. The clutch of this invention is further bidirectional in function, exhibiting the same breakpoint torque value regardless of whether torque is applied clockwise or counterclockwise. In use, a combination of the orientation of the UV module, gravity and location of the center of mass of the shutter extrusion may allow the clutch to be slightly easier to override when the shutters are forced toward a closed position. The use of the indexing design of the clutch of this invention and the shutter hard stops which may be built into the UV module assembly enable the instant clutch to automatically reengage to the desired open or closed shutter position when the overload torque condition has been rectified and the shutter drive gear motor energized. This semi-automatic re-engagement feature is advantageous when operating and maintaining a UV module, especially so for quickly and easily installing and/or removing UV lamps and exposing shutter reflectors for cleaning and other maintenance. Regardless of the breakpoint torque value of the clutch of this invention, its external dimensions remain the same.

The clutch of this invention can be easily adjusted to a desired breakpoint value suitable for any size UV module. Consequently a UV module may include a clutch of this invention with a breakpoint torque, which is specific to the length, hence weight, of the shutters for a module of that size. Consequently, clutch operation will be more reliable and consistent, regardless of the skill and knowledge of the persons assembling and/or servicing the module. Unlike the clutch of the prior art, there is no requirement for adjusting of spring tension, or the like, in order to achieve a clutch with a desired breakpoint torque. Rather a predetermined combination of wave springs, thrust washers, and quantity of detent balls is provided for each size module. In any specific clutch configuration a nominal breakpoint torque required to disengage the clutch is linearly proportional to the number of detent balls used. The shutter shaft flange, accordingly, may be manufactured to include a specific number of detent holes arranged in a radial array. The number of detent balls used may vary from a quantity of one to virtually any number necessary to achieve the desired breakpoint torque. Additionally, small increases in dimensions such as diameters of detent holes of the clutch plate can produce nonlinear, e.g. exponential, increases in breakpoint torque.

One advantage of the clutch of this invention is that specific breakpoint torque values may be realized by utilizing component combinations specific for each size of UV module.

Without changing any aspect of the physical size of the clutch of this invention, several breakpoint torque values may be obtained by altering the clutch components and the orientation of the clutch components.

For a specific clutch assembly, breakpoint torque values are dependable and repeatable. Special skills are not required to assemble or service the clutch and adjustment or experimentation is not required to obtain the desired breakpoint value. Breakpoint torque cannot be casually or accidentally altered externally. The clutch must first be disassembled in order to alter the breakpoint setting.

The clutch of this invention will function at the same predetermined breakpoint torque whether driven internally by the shutter shaft or manipulated externally by hand.

The breakpoint torque value may be adjusted during assembly by virtue of a specified combination of wave springs, thrust washers, and detent balls. An integral shutter drive pin may be incorporated into the shutter drive arm. Therefore, fewer threaded parts are required to be fabricated and installed. Additionally, fewer parts are present to be dropped or fall into an operating printing press during installation or servicing, potentially damaging the printing press or halting operation until retrieved.

The integral drive pin of this invention further provides a mounting location for a sensor magnet.

Although left-hand specific and right-hand specific shutter end caps are required, the components of the clutch of this invention are ambidextrous and will fit either shutter assembly.

The clutch subassembly of this invention is bidirectional and will exhibit the same breakpoint torque value regardless of whether torque is applied clockwise or counterclockwise in direction.

The clutch of this invention features a narrow profile, approximately 5/16 inch thick in one embodiment, including the retaining ring holding the clutch in place on the shutter shaft.

The clutch plate of this invention transfers torque from the shutter shaft to the shutter drive arm by means of a single drive tab, detent holes, and an array of detent balls.

By using the indexing clutch design of this invention and a special shutter hard stops built into the UV module assembly, the clutch of this invention may automatically reengage itself in the desired opened or closed shutter position once the overload torque condition has been rectified and the motor is energized.

During normal UV module shutter operation with the instant clutch engaged, there is no relative motion among the clutch components. These clutch components are therefore free of wear while the clutch is engaged.

During normal disengagement, only one main internal component, the clutch plate, moves relative to the other clutch components. During normal disengagement, the clutch plate rotates around the shutter shaft and moves axially a very small amount as its detent holes pass over the detent balls. Axial displacement of the clutch plate is on the order of 0.025+/−0.015 inch in one embodiment.

The single drive tab on the clutch plate always remains engaged inside the drive tab receiver slot within the shutter drive arm.

Realigning orientation of the shutter drive arm, relative to the shutter shaft, depends only on the number of detent balls in the clutch plate. Realignment orientation, accordingly, is not dependent on the number of detent balls employed, nor is it dependent on the number of detent holes arrayed around the shutter drive flange.

Whether or not the instant clutch is in an engaged or disengaged mode, the clutch is designed with features providing a highly desirable multi-axial freedom of motion enabling reliable functionality of the UV shutter module assemblies and the shutter drive train assembly. In a nominal over torque condition, there is very little or no linear displacement of the shutter drive arm, sensor magnet, or shutter end caps, relative to any part of the UV module. If a long term continuous torque overload situation occurs, there is minimal relative motion between clutch components. Accordingly the clutch components wear very little when the clutch is disengaged. The foregoing arrangement assures reliable clutch performance, reliable shutter action, reliable shutter position sensing, and produces no detrimental effect on the shutter shaft-to-shutter end cap seal arrangement. Thus, the clutch design of this invention contributes to minimizing shutter drive train binding, minimizing coolant leakage, and maximizing UV module reliability.

Regardless of the breakpoint torque value selected for a clutch of this invention, the external dimensions of the clutch remain unchanged.

The clutch of this invention is easily field serviceable, due to its simple design, small number of parts, and ease of assembly and disassembly.

It is understood that the above-described figures are only illustrative of the present invention and are not contemplated to limit the scope thereof.

DETAILED DESCRIPTION

Each of the features and methods disclosed herein may be utilized separately or in conjunction with other features and methods to provide improved embodiments of this invention and methods for making the same. Representative examples of the teachings of the present invention, which examples utilize many of these additional features and methods in conjunction, will now be described in detail with reference to the drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Therefore, combinations of features and methods disclosed in the following detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative and preferred embodiments of the invention

The clutch of this invention is advantageously present in a UV module100, as shown inFIG. 1. A more detailed description of a suitable embodiment of the UV module100is provided in co-pending U.S. patent application Ser. No. 12/001,080, filed Dec. 7, 2007, entitled, UV Module, and hereby incorporated by reference. The UV module100includes respective left and right shutter assemblies102,104. The left and right shutter assemblies102,104include respective left and right shutter end caps106,108and are, in turn, opened and closed by respective left and right clutch/pin drive assemblies110,112. The clutch/pin drive assemblies110,112are powered by a worm drive assembly114, which includes a drive gear motor116, which rotates a spur gear118. The spur gear118, in turn, meshes with, and rotates, a spur gear120, the spur gear120attached to an end of a worm shaft122. The worm shaft122includes opposed thread segments124,126. As more fully explained in U.S. patent application Ser. No. 12/001,080, the thread segments124,126oppositely rotate the left and right clutch/pin drive assemblies110,112when the shutter assemblies102,104are being opened or closed. Each of the end caps106,108defines a slot128,130(slot130not shown) within which a drive pin132of the clutch/pin drive assembly is present during operation. Shutter position sensors134,136detect whether the shutter assemblies102,104are in an open or closed position, respectively.

Referring toFIG. 2, a left shutter assembly150has a left shutter end cap152with a slot154in place of the drive slot128depicted inFIG. 1. In contrast to the drive slot128, drive slot154opens into, and can be accessed from, the periphery of the shutter end cap152. Also depicted inFIG. 2, is a left shutter drive assembly156replacing the left clutch/pin drive assembly110. Because the left shutter assembly150, left shutter end cap152, and left shutter drive assembly156are substantially mirror images of right counterparts, only the left embodiments of these components are discussed and described.

Referring now toFIGS. 3 and 4, the shutter drive assembly156has a shutter shaft160, a collar162, a drive gear164, a bearing spacer166, a bearing168, a shutter drive clutch assembly170, a bearing172, and seals such as0-rings174. The collar162and drive gear164, in one embodiment, may be substantially similar to the collar334and gears324,326disclosed in U.S. patent application Ser. No. 12/001,080, which are secured to the shutter shafts160as more fully explained below.

FIGS. 4,5,6, and7depict the shutter shaft160, which has a cylindrical body178, flanges180,182, and grooves184,186. A plurality of detent holes188extend inwardly from a face190of the flange182. The two piece collar162attaches to the shutter shaft160using the drive pin163. Individual pieces of the clamp collar162clamp securely to the shutter shaft160and the drive pin163protrudes from the collar162to engage a slot (not shown) in each of the worm gears164. When thusly secured, an angled shoulder (not shown) of the collar162abuts the flange (or shoulder)180of the shutter shaft160. As fasteners163secure the two-piece collar162to the shutter shaft160, one of the worm gears164is wedged toward the bearing-spacer (not shown). Each of the worm gears164is then tightly clamped in place between the clamp collar162and the spacer and is positioned to fully mesh with the left and right hand segments124,126of the worm shaft122.

Referring back toFIGS. 3 and 4, the shutter drive clutch assembly170has a shutter drive arm200, a clutch plate202, a clutch thrust washer204, a spring assembly such as at least one or a plurality of, e.g., two, wave (disk) springs206, respective inner and outer thrust washers208,210, and a retaining ring212. As seen inFIGS. 3,4, and8, the shutter drive arm200includes an extension such as a pin214having a bore216, which accommodates a sensor magnet218. As depicted inFIG. 8, the shutter drive arm200also has a shutter drive arm body220which defines an aperture222and has a cavity224. The cavity224opens into a slot226proximate the extension214and includes an intermediate, stepped ledge228. The purpose of the stepped ledge228is to minimize the amount of undesirable “twisting” motion of the instant clutch assembly which could occur when a shutter was being opened or closed.

Referring now toFIG. 9, the clutch plate202has an extension such as a tab234depending from a body236. The body236is generally circular in cross section, defines a cavity238, an aperture240, and a plurality of detent holes242. The tab234is dimensioned to be accommodated in the shutter drive arm slot226when the clutch plate202is accommodated within the shutter drive arm cavity224.

When assembled as shown inFIGS. 4 and 11, the flange182is disposed against the ledge228and a plurality of balls244are disposed within each of the flange detent holes188and within the clutch plate detent holes242, as the clutch plate202is disposed within the shutter drive arm body220. The clutch thrust washer204is disposed so as to contact the clutch plate body236within the clutch plate cavity238. The wave springs206are then held in contact with the clutch thrust washer204by the inner thrust washer208. The foregoing assembly of components is then maintained against the shutter drive arm body220by the outer thrust washer210, which is, in turn, secured by the retaining ring212positioned in slot186.

The instant clutch170, in one embodiment, is primarily built around the shutter shaft160and the shutter shaft integral flange182. Coolant flows into, or out of, the UV module shutters through shutter shaft160. The integral flange182maintains in place the detent balls244. The shutter drive arm200, clutch plate202, and shutter end cap152rotate about the shutter shaft160. The shutter shaft160thus acts as a precision bearing surface and provides concentric positioning for each of the foregoing components. Though not considered an actual clutch component, the shutter shaft bearing168supports the shutter shaft160and maintains the axial position of the shutter shaft160and clutch assembly170, relative to the UV module.

The shutter drive arm200may rotate about the shutter shaft160and is held in place on the shutter shaft160with a retaining ring212. The shutter drive arm200also features an integral drive pin214and a single drive tab receiver slot226. Installed in the drive pin is a sensor magnet218. The shutter drive arm200houses the majority of the functional components of the clutch and its geometry assists in maintaining correct alignment of these components.

One purpose of the clutch plate202is to transfer torque from the shutter shaft160to the shutter drive arm200. The clutch plate202accomplishes this by means of its single drive tab234, detent holes242, and detent balls244. The detent balls244are always present in respective detent holes188in the shutter shaft flange182. The detent balls244may, however, exhibit a small degree of spin while the instant clutch is disengaged and is attempting to re-engage. The detent balls244perform two tasks. While the instant clutch is in an engaged mode, the detent balls244act as a set of keys to positively mate the shutter flange182to the clutch plate202. The detent balls also provide a ramp for the detent holes242. This ramp feature provides the necessary resistance against clutch disengagement. Additionally, the ramp feature serves to “encourage” re-engagement of the instant clutch. The number of detent balls244used may vary according to the “break-point” desired for the particular clutch embodiment.

Two different sets of detent holes are used in the instant clutch. The first set188is present in a radial array with a specific radius “r” on the inside face10of the shutter flange182. These detent holes188are slightly larger in diameter than the detent balls244and are machined to a controlled depth, thus assuring that a pre-determined portion of the detent ball244protrudes beyond the face of the shutter flange182. These detent holes188receive and retain the detent balls244in their respective positions by means of dimensions such as their diameter and depth and by forces generated by the thrust washer208, wave spring(s)206, and clutch plate202biased against the detent balls244. The second set of detent holes242is present in the clutch plate202. These detent holes242are also machined in a radial array with the same specific radius “r,” but may have a diameter smaller than that of the detent balls244. This arrangement produces a specific and repeatable amount of partial engagement of a specific detent ball244to a detent hole242. The performance of the instant clutch may be dependent upon this particular engagement of balls244to detent holes242. In some embodiments, slots arranged in a radial array may be substituted for the round detent holes in the instant clutch plate.

Wave springs206force the clutch plate202against the detent balls244to thereby maintain clutch engagement or to effect clutch re-engagement. The wave springs206may be selected for a desired spring constant. The performance of the instant clutch may be highly dependent upon the force generated by the wave springs206.

Thrust washer204acts as a bearing surface to transfer and distribute axial forces generated by the wave springs206. Thrust washer204thus tends to more evenly distribute the concentrated “point” forces developed at the crests243of the wave spring(s)206. Thrust washers204,208,210may thus offer a degree of pre-load force adjustment for the wave spring(s)206, which may ultimately affect the breakpoint torque value for the clutch of this invention. Breakpoint adjustment may be accomplished, in part, by specifying certain thrust washer thicknesses, either individually or by creating specific thickness combinations using several thrust washers.

Though not considered an actual clutch component, the shutter end cap152is driven directly by the shutter drive pin214. By virtue of the securement of the shutter end cap152to the shutter flange182, driving the shutter end cap152opens or closes the instant shutter assembly.

A sensor magnet218may be present in the shutter drive pin214. Sensors134,136mounted within the instant UV module monitor the “open” or “closed” position of the instant shutter assembly by sensing proximity of the sensor magnet218.

During normal UV module operation, shutter drive forces originating in the shutter drive gear motor116are transferred to the shutter shaft160by a gear combination shown inFIG. 1. These forces, in turn, are transmitted via the detent balls244and detent holes242in the clutch plate202. The drive tab234, integral to the clutch plate202in one embodiment, is engaged in a slot226in the shutter drive arm200, effectively transferring drive torque from the clutch plate202to the shutter drive arm200. The shutter drive arm202also includes an integral drive pin214, which is engaged in a slot154in the shutter end cap152.

The detent holes242in the clutch plate202are smaller in diameter than the detent balls244. The smaller detent holes242allow the detent balls244to enter only partially into the detent holes242, thereby resulting in a carefully controlled amount of ball-to-hole engagement. This foregoing arrangement creates a specific “climb-out” angle of a detent ball244relative to the rim of the detent hole242. This “climb-out” angle directly affects the breakpoint torque of the clutch. The drive tab234on the clutch plate202is in continual engagement with the receiver slot226within the shutter drive arm200and the integral drive pin214on the shutter drive arm200is in continual engagement with a slot154in the shutter end cap152.

By means of the foregoing components, the drive forces originating at the shutter drive gear motor116are subsequently transmitted to open or close the instant shutter assembly150or to hold the shutter assembly150in either the open or closed positions. The instant clutch further provides the protection of a torque overload device. Additionally, the instant clutch functions in conjunction with the shutter end cap seal/bearing arrangement to provide sufficient freedom of motion to prevent gear train damage.

When the instant clutch is fully engaged as shown inFIG. 4, the clutch operates in a completely static condition. There is no relative motion between any of the clutch components, shutter shaft, or shutter end cap. The wave springs206constantly force the clutch plate202against the detent balls244embedded in the flange182of the shutter shaft160. In this “clutch engaged” condition, all detent balls244remain seated in detents242within the clutch plate202. A nominal over-torque condition may occur during a gear motor-powered shutter operation or by manipulating the shutter manually. In a nominal over-torque condition, the clutch plate detent holes242disengage from the balls244present in the flange182of the shutter shaft160. This disengagement is a result of the rims of the detent holes242in the clutch plate202“climbing” over the stationary detent balls244. During this period of disengagement and as shown inFIG. 12, the clutch plate202is minimally displaced axially away from the shutter shaft flange182. Except for friction forces induced by the wave springs206against the thrust washer204and detent balls244riding along the face236of the clutch plate202between detent holes242, drive forces are effectively reduced to a minimum amount at the shutter drive arm200. Stated otherwise, due to this small amount of internal friction, a disengaged clutch of this invention does not lend itself to be considered to be a true “free-running” type clutch. Even when the clutch is disengaged, a small amount of driving force may be produced by friction between the detent balls244and the clutch plate202.

When the shutter drive motor116is energized during a “disengaged” situation, the shutter shaft160continues to rotate relative to the shutter drive arm200. The detent balls244continually attempt to reengage the clutch plate202each time the clutch plate detent holes242are aligned with the detent balls244. Re-engagement occurs when two conditions are met: 1) the over-torque condition must be corrected; and 2) the rotary position of the clutch plate202must be so as to allow the detent balls244to realign with the detent holes242in the clutch plate202. Due to this characteristic of the clutch attempting to reengage intermittently, the clutch maybe classified as an “indexing” type. Other than the small displacement of the clutch plate202during disengagement, there is no other axial motion of any other component, except for the slight compression of the wave springs206and thrust washer204, that the wave spring206is biased against. The detent balls244remain in place in detent holes188in the shutter flange182. The frequency of reciprocation of the clutch plate202is thus not dependent on the number of detent balls244, but rather is dependent on the rotational speed of the shutter shaft160, relative to the shutter drive arm200(or vice versa) and on the number of detent holes242in the clutch plate202. Realignment orientation of the shutter drive arm200relative to the shutter shaft160is dependent only on the number of detent holes242in the clutch plate202. Realignment orientation is thus not dependent on the number of detent balls244employed, nor is it dependent on the number of detent holes188arrayed about the shutter drive flange182.

Axial displacement of the clutch plate202may be partially dependent on the size of the detent balls244in the shutter flange182relative to the size of the mating detent holes242in the clutch plate202and partially dependent on the depth of the detent holes188in the shutter shaft flange182. In practice, the amount of axial displacement may be a small fraction of the diameter of a detent ball. The actual nominal displacement range may be on the order of 0.025+/−0.015 inch.

Because numerous modifications of this invention may be made without departing from the spirit thereof, the scope of the invention is not to be limited to the embodiments illustrated and described. Rather, the scope of the invention is to be determined by the appended claims and their equivalents.