Background Art A typical liquid filter has a tank divided horizontally into an upper tank and a lower compartment.

The upper tank receives dirty liquid to be filtered. A perforated plate or porous septum/screen separates the upper tank and the lower compartment. Filter media, such as a paper web, is driven across the perforated plate. A vacuum in the lower compartment induces liquid flow from the upper tank through the filter media and the perforated plate into the lower compartment. Such filters are used in connection with the filtration of machine tool liquid coolant in which cutting chips and other solid debris are filtered from the coolant by the filter media prior to being recirculated back to machine tools.

Filter media can take the form of disposable media (paper or roll) or a permanent or recleanable media belt. The permanent media belt is indexed peri- odically through the tank as the belt becomes clogged to advance a fresh segment onto the perforated plate. Each indexed segment is cleaned and recirculated back under

the tank and then over the perforated plate. Alterna- tively, a disposable media strip can be indexed periodi- cally, each segment of which is collected for disposal after use. Both permanent and disposable media may be used in combination with the disposable media overlying the permanent media.

Filter media is often driven by a drag con- veyor having a pair of spaced apart chain loops connect- ed by flights extending across the width of the media.

The flights carry the removed solids filtered by the filter media such as machining chips out of the tank.

The drag conveyor frictionally drives the permanent media belt. The weight of the chain loops and the flights of the drag conveyor bears on edges of the media belt to seal the same and create a frictional engagement to carry the media belt through the tank as the conveyor is periodically indexed. Only frictional engagement is used with disposable media.

A problem with frictionally driving the permanent media belt is that it is difficult to remove or replace the belt if it breaks during use. Another problem is the uneven wear on the permanent media belt.

What is needed is another pair of drive loops for driving the permanent media belt independently of the pair of drive loops driving the drag conveyor.

Summary Of The Invention Accordingly, it is an object of the present invention to provide a filter having a first pair of drive loops for driving a permanent filter belt and a second pair of drive loops for driving a drag conveyor.

It is another object of the present invention to provide a filter in which a drag conveyor and a permanent filter belt may be driven at the same or different speeds.

In carrying out the above objects and other objects, the present invention provides a filter appa- ratus including an upper tank for holding dirty liquid and having a perforated plate. A lower compartment is beneath the perforated plate for receiving liquid from the upper tank through the perforated plate. The filter apparatus further includes a permanent filter belt for filtering particulate from the dirty liquid. The permanent filter belt is arranged in a first circulating path across the perforated plate. A first pair of spaced apart drive loops are attached on respective sides of the permanent filter belt.

The filter apparatus also includes a drag con- veyor having a series of spaced apart flights. The drag conveyor is arranged in a second circulating path across the perforated plate. The permanent filter belt is positioned between the perforated plate and the flights of the drag conveyor across the perforated plate. A second pair of spaced apart drive loops are attached on respective sides of the flights.

A driving mechanism is operable with the first and second pairs of drive loops for indexing the per- manent filter belt and the drag conveyor along the respective circulating paths such that a fresh segment of the permanent filter belt is periodically indexed over the perforated plate while a dirty segment of the permanent filter belt is being cleaned and the flights of the drag conveyor are periodically indexed to carry away accumulated particulate filtered by the permanent filter belt.

Further, in carrying out the above objects and other objects, the present invention provides a method for moving the permanent filter belt and the drag conveyor of the above-described filter apparatus. The method includes attaching the permanent filter belt across a first pair of spaced apart drive loops and attaching the flights of the drag conveyor across a second pair of spaced apart drive loops. The first and second pairs of drive loops are then driven to move the permanent filter belt and the drag conveyor along the respective circulating paths such that a fresh segment of the permanent filter belt is periodically indexed over the perforated plate while a dirty segment of the permanent filter belt is being cleaned and the flights of the drag conveyor are periodically indexed to carry away accumulated particulate filtered by the permanent filter belt.

The advantages accruing to the present in- vention are numerous. For instance, the extra pair of drive loops makes it much easier to remove, repair, and replace the permanent filter belt.

These and other features, aspects, and em- bodiments of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings.

Brief Description Of The Drawings FIGURE 1 is a side elevational view of a filter embodying the present invention; FIGURE 2 is a top plan view of the filter shown in Figure 1; FIGURE 3 is a side view of the filter shown in Figure 1; FIGURE 4 is a cross-sectional view of the arrangement of the first and second pairs of chain loops of a filter embodying the present invention; FIGURE 5 is a bottom plan view of the arrange- ment of the first and second pairs of chain loops shown in Figure 4; FIGURE 5 is a view of the permanent filter belt of a filter embodying the present invention; FIGURE 7 is a top view illustrating the single connection between the segments of the permanent filter belt shown in Figure 6; FIGURE 8 is a cross-sectional view of the single connection between the segments of the permanent filter belt shown in Figure 7 along the line 8-8; and

FIGURE 9 is a schematic illustrating the driving arrangement for driving the first and second pairs of chain loops.

Best Modes For Carrying Out The Invention Referring now to Figure 1, a liquid filter 20 in accordance with the present invention is shown. Fil- ter 20 includes a tank 22 provided with an upper tank 24 and a lower compartment 26. Upper tank 24 receives dirty liquid from a system requiring the return of filtered liquid for reuse in the system. A perforated plate 28 supported over tank floor 30 separates upper tank 24 from lower compartment 26. Perforated plate 28 is a metal screen or the like.

A permanent filter belt 32 interposes between upper tank 24 and perforated plate 28 to capture and retain contaminants from dirty liquid passing into lower compartment 26 through a segment of the filter belt overlying the plate. A pump 34 is connected to lower compartment 26 for generating a vacuum in the lower compartment to cause liquid to flow through permanent filter belt 32 into the lower compartment. The filtered liquid flows through pump 34 to the system for reuse (not specifically shown).

Permanent filter belt 32 is an endless belt arranged to recirculate along a first circulating path down the inside of tank entrance wall 36, above and across perforated plate 28, up the inside of inclined tank exit wall 38, out of tank 22, back across the space below-lower compartment 26, and back up the outside of tank entrance wall 36 prior to reentry into the tank.

Permanent filter belt 32 is supported on idler wheels 40 along the first circulating path to be freely movable therealong. A first pair of spaced apart endless drive loops 41 such as chain loops (as shown) or belt loops drives permanent filter belt 32. Chain loops 41 drive permanent filter belt 32 to periodically advance a fresh segment onto perforated plate 28.

A second pair of spaced apart endless drive loops 42 such as chain loops (as shown) or belt loops each adjacent one sidewall of tank 22 drives a drag conveyor 44. Drag conveyor 44 includes flights 46 extending across the width of tank 22 connecting chain loops 42.

Drag conveyor 44 is arranged to recirculate along a second circulating path in tank 22 so that flights 46 carry removed solids such as machining chips out of the tank. Drag conveyor 44 recirculates along the second circulating path down the inside of tank en- trance wall 36, above and across perforated plate 28, up the inside of inclined tank entrance wall 36, and back through the top portion of upper tank 24. Drag conveyor 44 is supported on idler wheels 48 along the second circulating path to be freely movable therealong.

In operation, permanent filter belt 32 is driven counter-clockwise along the first circulating path and drag conveyor 44 is driven clockwise along the second circulating path. Permanent filter belt 32 and drag conveyor 44 converge above tank 22 near tank entrance wall 36 at the point indicated by reference numeral 54. From point 54, permanent filter belt 32 and drag conveyor 44 travel along the same direction with

flights 46 of the drag conveyor 44 overlying the perma- nent filter belt. Permanent filter belt 32 and drag conveyor 44 travel from point 54 across perforated plate 28 with the permanent filter belt interposed between the perforated plate and flights 46 of the drag conveyor.

Dirty liquid from upper tank 24 is then fil- tered by permanent filter belt 32 and passes through perforated plate 28 into lower compartment 26. Perma- nent filter belt 32 is indexed to move a fresh segment over perforated plate 28 once the permanent filter belt becomes clogged with filtered particulate from the dirty liquid. Drag conveyor 44 is also indexed periodically so that flights 46 carry the filtered particulate away from perforated plate 28, up the inside of inclined tank entrance wall 36, and out of tank 22 at the point indicated by reference numeral 55.

Permanent filter belt 32 and drag conveyor 44 diverge at point 55 such that the permanent filter belt travels back through lower compartment 26 while the drag conveyor travels back through the upper portion of upper tank 24. Permanent filter belt 32 and drag conveyor 44 subsequently meet at point 54 and the process repeats such that a segment of the permanent filter belt and a portion of the drag conveyor are constantly over perfo- rated plate 28.

Filter 20 may further include a disposable filter strip 50 mounted in a roll 52 above tank 22 near tank entrance wall 36. Because permanent filter belt 32 and drag conveyor 44 meet at point 54, disposable filter strip 50 can be introduced between flights 46 and the permanent filter belt. Disposable filter strip 50 rests

on, and is carried by, permanent belt 32 as they togeth- er pass over perforated plate 28. In the event perma- nent filter belt 32 is removed, drag conveyor 44 then frictionally drives disposable filter strip 50. Dispos- able filter strip 50 then travels through tank 22 across perforated plate 28 and then out of the tank at point 55 where it may be collected for disposal.

Permanent filter belt 32 includes a porous flexible strip material of suitable durability, such as a synthetic or natural fiber woven fabric. Disposable filter strip 50 is a commercially available porous paper.

A wash station 56 positioned outside of tank 22 along tank exit wall 38 cleans permanent filter belt 32. Wash station 56 includes a scraper 58, a water nozzle 60, and an air nozzle 62 positioned over a collection trough 64.

A drive mechanism 66 includes a drive belt 68 for driving the first pair of chain loops 41 and the second pair of chain loops 42.

Referring now to Figures 2 and 3, with con- tinual reference to Figure 1, tank 22 further includes a primary tank 80 mounted to one sidewall 82 of the tank. Primary tank 80 includes an upper compartment 84 and a lower compartment 86. A perforated plate 88 separates upper compartment 84 from lower compartment 86. Lower compartment 86 is connected to upper tank 24 at outlet portion 90.

In operation, upper compartment 84 receives dirty liquid to be filtered. The dirty liquid passes through perforated plate 88 into lower compartment 86. Perforated plate 88 is suitable for filtering large sized contaminants out of the dirty liquid. On the other hand, perforated plate 28 is suitable for fil- tering out much smaller sized contaminants. Accord- ingly, primary tank 80 provides a first stage of rough filtering and tank 22 provides a second stage of fine filtering.

Primary tank 80 includes a drag conveyor 92 driven by a third pair of spaced apart endless drive loops 94 such as chain or belt loops. Drag conveyor 92 includes flights 96 for carrying away from upper com- partment 84 the larger sized contaminants filtered out by perforated plate 88. A drive mechanism 98 includes a drive belt 100 for driving the third pair of chain loops 94.

Turning now to Figures 4-6, permanent filter belt 32 and the arrangement of first and second pairs of chain loops 41 and 42 are illustrated in further detail.

Permanent filter belt 32 includes a main filter section 101 and two spaced apart attachment portions 102 at each end of the main filter section. Disposable filter strip 50 may be interposed between permanent filter belt 32 and flights 46. Spaced apart grommets 104 run along attachment portions 102.

First pair of chain loops 41 includes grommet attachments 106 such as lugs or the like. Grommet attachments 106 are attached to links of each of chain loops 41 and are arranged periodically to extend in-

wardly therefrom into tank 22. Grommets 104 attach to grommet attachments 106 by screws 108 or the like such that permanent filter belt 32 extends between chain loops 41.

Flights 46 of drag conveyor 44 are attached across links of second pair of chain loops 42. As seen best in Figures 4-5, unlike the liquid filters of the prior art, permanent belt filter 32 is driven indepen- dently of drag conveyor 44. That is, permanent belt filter 32 is not attached or frictionally engaged with drag conveyor 44 or chain loops 42. Permanent belt filter 32 is directly attached to chain loops 41 which are dedicated for the sole use of the permanent belt filter.

Preferably, permanent belt filter 32 includes segments that are connected together at a single loca- tion. Accordingly, the length of permanent belt filter 32 may be shortened or lengthened by adjusting the segments accordingly and then connecting them together at the single location.

As shown best in Figures 7-8, permanent belt filter 32 includes segments 120 (a-b). Segments 120 (a-b) are connected together by a hinge pin 122. Hinge material 124 surrounds hinge pin 122. A resin/glue mixture section 126 supports hinge material 124 to main filter section 101 of segments 120 (a-b). A hook and loop fastener strip 128 is provided on segment 120a near hinge pin 122. A flap 130 attaches to strip 128 to connect segment 120b to segment 120a.

Referring now to Figure 9, a schematic il- lustrating drive mechanism 66 for driving first and second pairs of chain loops 41 and 42, respectively, is shown. Drive mechanism 66 includes a motor 140 having a drive shaft 142 for imparting rotary energy. Drive shaft 142 is connected to a drive sprocket 144. Drive belt 68, shown as a chain as shown in Figure 9, engages drive sprocket 144. Drive chain 68 couples a drag con- veyor shaft 146 and an idler shaft 148 to drive shaft 142.

Drive chain 68 engages a sprocket 150 attached to drag conveyor shaft 146 for driving the drag conveyor shaft in a given direction. A sprocket 160 is attached to drag conveyor shaft 146. Second pair of chain loops 42 engage sprocket 160 to move in the given direction when drive chain 68 drives drive conveyor shaft 146.

Similarly, drive chain 68 engages a sprocket 152 attached to idler shaft 148 for driving the idler shaft in the given direction. Idler shaft 148 includes an idler gear 154.

A gear 158 attached to permanent filter belt shaft 156 is operable with idler gear 154 such that drag conveyor shaft 146 and the permanent filter belt shaft rotate in opposite directions when driven by drive chain 68. A sprocket 162 is attached to permanent filter belt shaft 156. First pair of chain loops 41 engage sprocket 162 to move in a direction opposite the given direction when drive chain 68 drives permanent filter belt shaft 156.

As known to those of ordinary skill in the art, gears 154 and 158 may have different tooth configu- rations such that drag conveyor shaft 146 and permanent filter belt shaft 156 rotate in opposite directions at different speeds. Accordingly, permanent filter belt 32 and drag conveyor 44 may move at different speeds along their respective circulating paths. Of course, gears 154 and 158 may have the same tooth configurations such that shafts 146 and 156 rotate at the same speed.

Thus it is apparent that there has been provided, in accordance with the present invention, a filter having dual drive loops for driving a permanent media belt and a drag conveyor that fully satisfies the objects, aims, and advantages set forth above.

While the present invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifica- tions, and variations as fall within the spirit and broad scope of the appended claims.