Guard and control apparatuses for sliding compound miter saw

Abstract: A guard assembly (20) for a saw or other cutting device includes fixed (40) and movable guards (42) relatively pivotal by way of a linkage assembly (46) having two links (48,50) pivotally interconnected coaxially with a cam roller (52) engageable with a cam surface (54) for controlling relative guard movement. Other preferred features include a torsional coil guard return spring (70) and spring enclosure (72) that minimises interference with workpiece cutting depth, an arbor shaft cover retention fastener (69) that doubles, along with another caliper member, as a blade caliper set that prevents guard damage in the event of a bent or deflected blade or cutter, a drive assembly hold-down assembly for storage, and a horizontally-extending handle centred horizontally relative to the blade or cutter.

Description: The present invention relates primarily to a cutting device for performing cutting operations such as a power chop-type saw, miter saw, compound miter saws or other power operated equipment or machinery utilising a blade or other cutter for performing cutting operations on workpieces composed of wood, metal, plastic or other materials. More particularly, the present invention seeks to achieve various improvements in blade guard mechanisms for such power operated equipment, typically having a lower movable guard pivotally movable relative to a fixed upper guard between "closed" and "open" positions as the blade is pivotally moved between non-cutting and cutting positions. Preferred forms of the present invention also relate to improvements in blade or cutter arbor shaft covers and to blade or cutter calipers in conjunction with the guard mechanism, as well as to a blade or cutter hold-down arrangement for preventing operation of the saw when in a locked-down state. Still another preferred form of the invention includes advantageous improvements in the operator handle position, orientation and configurations that optimise the user's comfort and control of the blade or cutter when performing a wide variety of cutting operations. Saws and other apparatuses designed for cutting or performing other working operations on a workpiece typically include mechanisms for setting the saw blade or cutting tool in selected angular relationships with the workpiece when performing various cutting operations. Examples include chop-type compound miter saws adapted for allowing the user to selectively set the saw blade at any of a number of positions or modes for square cutting, miter cutting, bevel cutting, or even compound miter cutting in which combination miter angle and bevel angle cutting operations are performed on the workpiece. In addition, some operations, such as dado cutting, groove cutting, or shaping operations, for example, require the use of saw blades or other cutting or working devices of different shapes or sizes to be substituted for one another in order to perform the desired operation on the workpiece. In these instances, the saw or cutting device must be capable of cross-cutting or sliding movement of the blade or cutting tool in lieu of, or in addition to, chop-type engagement with the workpiece. In order to allow for the setting of miter and bevel angles, the saw blade, cutter or other working device is angularly adjustable with respect to both a horizontal base and a vertical fence against which the workpiece is positioned. The miter adjustment allows the saw blade, cutter or other working device to be angularly positioned with respect to the vertical fence while maintaining perpendicularity with the horizontal base. The bevel adjustment allows the saw blade, cutter or other working device to be angularly positioned with respect to the horizontal base while maintaining perpendicularity with the vertical fence. Various combinations of miter angles and bevel angles are accomplished by simultaneously adjusting the angularity of the blade with respect to both the horizontal base and the vertical fence. In any of these cutting operations whether they are performed on chop-type, cross-cut, or combination type devices, a blade guard mechanism must be capable of exposing a sufficient portion of the blade to perform the desired cutting operation, while at the same time adequately protecting the operator during cutting and when the blade is in an at-rest position. Such a guard mechanism also should preferably protect the guard from damage in the event of a bent or deflected blade or cutter during such operations, should prevent the blade or cutter from vibrating loose from or on its arbor shaft during such operations, and should allow for maximum user comfort and control when performing such operations. Preferably, undesired operation of the saw or other such device should be prevented when in a storage or inoperative state. Unfortunately, many conventional devices have proved to be deficient in meeting some or all of these objectives, or have required burdensome multiplicities of parts or components in order to achieve them. Thus, many of such conventional devices have also often been found to be heavy and overly complex, difficult and expensive to design, manufacture and maintain, as well as requiring large spaces in which to operate them. In some cases, meeting these objectives has also resulted in unduly limiting cutting capacities. EP 0538066 discloses a miter saw according to the preamble of claim 1. According to the present invention, there is provided a cutting device for performing cutting operations on a workpiece, said cutting device comprising: a base assembly for receiving the workpiece; a support assembly interconnected with said base assembly; a drive assembly including a motor, an arbor shaft rotatable about an arbor axis, and a cutting tool driven by said motor about said arbor shaft, said drive assembly being pivotally interconnected with said support for selective pivotal movement of said motor and said cutting tool relative to said support assembly between an at-rest position wherein said cutting tool is out of engagement with the workpiece when the workpiece is on said base and an operational position wherein said cutting tool is in a cutting engagement with the workpiece when the workpiece is on said base; a guard assembly including a fixed guard partially surrounding a cutting periphery of said cutting tool, a movable guard, said fixed guard being fixedly interconnected with said drive assembly, and said movable guard being pivotally interconnected with said drive assembly for pivotal movement about said arbor shaft between a closed position surrounding a predetermined portion of the cutting periphery of said cutting tool and an open position covering a lesser portion of the cutting periphery of said cutting tool than when in said closed position, and a linkage assembly for drivingly moving said movable guard between said closed and said open positions as said drive assembly is moved between said at-rest and said operational positions, respectively; and a locking mechanism for preventing pivoting downwardly the drive assembly; wherein said linkage assembly comprises: a first link having an inner end pivotally interconnected with said support at a fixed location thereon and an opposite intermediate end; a second link having an outer end pivotally interconnected with said movable guard and an opposite intermediate end pivotally interconnected with said intermediate end of said first link for pivotal movement relative thereto about an intermediate linkage axis; an intermediate roller rotatably interconnected with said intermediate ends of said first and second links for rotation about said intermediate linkage axis; and a cam surface fixed relative to said drive assembly and said fixed guard and engageable by said roller for rotation of said roller thereon. A return spring can be advantageously included in the guard linkage assembly for resiliently biasing the movable guard toward a normally closed position covering a maximum portion of the cutting periphery of the blade or cutter. Such return spring is preferably a torsional coil spring with one anchoring end or leg interconnected with the fixed guard or drive assembly (at a fixed location thereon) and an opposite end or leg interconnected with the movable guard (also at a fixed location thereon). An off-centre spring enclosure, which is radially offset relative to the arbor shaft, is preferably included for restricting radial expansion of the torsional spring to directions away from the workpiece (on opposite sides of the arbor shaft from the workpiece) in order to maximise the workpiece cutting depth capacity of the saw blade or cutter. Another optional but preferred feature of the invention is an arbor shaft cover that is pivotally interconnected with the fixed guard and that substantially prevents or minimises any tendency of the arbor shaft nut, screw or other blade-securing fastener to work loose on, or free of, the arbor shaft. Such arbor cover can be pivoted out of the way to allow blade removal or blade changing by way of a releasable cover retaining fastener at one end of the pivotal cover, with such retaining fastener also optionally being configured to extend axially inside the fixed guard when tightened so as to act as one of a pair of blade calipers axially spaced from opposite sides of the blade or cutter. Such calipers thereby prevent or substantially minimise damage to the fixed guard in the event of a bent or deflected blade or cutter. A hold-down strap member can also be included and be can pivotally interconnected with the saw's base for movement between a storage position and a hold-down position in releasable engagement with the saw's drive assembly in order to releasably secure the drive assembly in a lowered storage position relative to the base. Also, the operator handle of the saw preferably includes a horizontally extending gripping portion that is generally centred laterally with respect to the plane of the blade or cutter. This contributes advantageously to workpiece visibility, ease of use, and operator control of the saw or other cutting device so equipped. An embodiment of a sliding compound miter saw will now be further described with reference to the accompanying drawings, in which: Figure 1 is a front perspective view of a sliding compound miter saw; Figure 2 is a front elevational view of the sliding compound miter saw shown in Figure 1; Figure 3 is a rear elevational view of the sliding compound miter saw shown in Figures 1 and 2; Figure 4 is a right-hand side elevational view of the sliding compound miter saw shown in Figures 1 through 3; Figure 5 is a partially exploded perspective view of a preferred blade guard mechanism in accordance with the present invention; Figure 6 is another partially exploded perspective view of the blade guard mechanism of Figure 5, revealing still further details of its preferred construction; Figure 7 is a partial exploded detail view of the movable portion of the guard mechanism shown in Figures 5 and 6, illustrating in more detail the guard-opening linkage arrangement; Figure 8 is a partial cross-sectional detail view of the lower guard return spring and spring enclosure arrangement of the guard mechanism of Figures 5 through 7; Figures 9a through 9c schematically illustrate the resilient flexing of the preferred torsional lower guard return spring at various movable lower guard positions for the preferred guard mechanism of Figures 5 through 8; Figures 10a through 10d are diagrammatic views, with parts removed or broken away, to schematically illustrate the operation of the linkage arrangement for controlling the lower guard movement between workpiece non-engagement and engagement positions for the blade or cutter of the saw illustrated in Figures 1 through 9; Figure 11 is a partial left-hand side view of the preferred guard mechanism, illustrating the blade arbor shaft cover in an operating position; Figure 12 is a partial exploded view, further illustrating the arbor shaft cover arrangement of Figure 11; Figures 13a and 13b are partial cross-sectional views, illustrating a blade caliper arrangement incorporated into the arbor shaft cover arrangement; Figures 14a and 14b are partial perspective views of a hold-down arrangement for the preferred sliding compound miter saw depicted in Figures 1 through 13; Figures 15a and 15b are partial front views of the guard locking mechanism for the sliding compound miter saw depicted in Figures 1 through 13; Figure 16 is a block diagram of a control circuit for operating a switched reluctance motor that drives the saw blade; and Figures 17a and 17b are partial right-hand side views of the back latch mechanism for the sliding compound miter saw depicted in Figures 1 through 15. Figures 1 through 17 depict exemplary embodiments of a sliding compound miter saw according to the present invention, which is shown in the drawings merely for purposes of illustration. One skilled in the art will readily recognise, from the following description, taken in conjunction with the accompanying drawings and claims, that the principles of the invention are equally applicable to compound miter saws and/or chop saws of types other than that depicted in the drawings. Similarly, one skilled in the art will readily recognise that the principles of the invention may also be applicable to other workpiece cutting, forming or shaping devices. In Figures 1 through 4, an exemplary sliding compound miter saw incorporating a cutter or blade guard mechanism, as well as other features according to the present invention, is designated generally by the reference numeral 10. The sliding compound miter saw 10 includes a base assembly 12, an angularly movable turntable or table assembly 14, an angularly movable housing assembly 16, a saw blade 18, a blade guard mechanism or assembly 20, a motor 22 drivingly connected to the saw blade 18 by way of a drive assembly 36, a handle arrangement 24, and a workpiece-supporting fence assembly 26. The table assembly 14 is secured to the base assembly 12 such that it can be rotated in order to provide adjustment for miter cutting of a workpiece 13 (shown in phantom lines in Figure 4). The rotation of the table assembly 14 changes the angle of saw blade 18 relative to the fence assembly 26 but maintains the perpendicularity of the plane of the saw blade 18 with the table assembly 14. A locking mechanism 28 can be activated in order to lock the table assembly 14 to the base assembly 12 at a desired miter-cutting position. The housing assembly 16 is secured to the table assembly 14 such that it can be pivoted with respect to the table assembly in order to provide adjustment for bevel cutting of the workpiece 13. The bevel pivoting of the housing assembly 16 changes the angle of the saw blade 18 relative to the table assembly 14 but maintains the perpendicularity of the saw blade 18 with respect to the fence assembly 26. A locking mechanism 30 can be activated in order to lock the housing assembly 16 to table assembly 14 at a desired bevel-cutting position. As can be appreciated by one skilled in the art, the adjustments for mitering and beveling can be performed separately or simultaneously in order to perform a compound miter and bevel cut. The housing assembly 16 also includes a support housing or assembly 32, which mounts a pair of support arms 34 for sliding movement with respect to the remainder of the housing assembly 16. The saw blade 18, the blade guard 20, the motor 22 and the handle 24 are all mounted to a drive assembly 36, which is pivotally interconnected with the support arms 34 and thus the support assembly 32. The pivoting of the drive assembly 36 downwardly towards the table assembly 14 operates to bring the saw blade 18 into a workpiece-engaging position and simultaneously open the blade guard 20 (as is described in more detail below) in order to cut a workpiece which is supported by the table assembly and the fence assembly 26. The sliding movement of the support arms 34 relative to the housing 16 permits the drive assembly 36 and thus the saw blade 18 to be pulled or pushed through the workpiece. Referring to Figures 1 through 8, the blade guard assembly 20 includes a fixed upper blade guard 40 and a movable lower blade guard 42. The movable guard 42 is interconnected for pivotal movement about an arbor shaft axis 45 of a blade arbor shaft 44 between a "closed" position, wherein the movable guard 42 covers a maximum portion of the cutting periphery of the blade 18, and an "open" position covering a minimum portion of the cutting periphery of the blade 18 in order to allow the blade 18 to perform cutting operations on the workpiece 13 and to allow for blade removal or replacement. The blade guard assembly 20 also includes a linkage assembly 46, which functions to pivot the movable guard 42 between its open and closed positions as the drive assembly 36 is pivoted by the operator about a pivot pin 38 (Figure 5) toward and away from the workpiece 13, respectively. This motion of the movable guard 42 with respect to the fixed guard 40 is further described below and is diagrammatically and schematically illustrated in Figures 10a through 10d (in which various parts of the compound miter saw are removed or broken away for clarity). The linkage assembly 46 includes a first link 48 having an inner end 56 pivotally interconnected with the support assembly 32 at a fixed location thereon. The linkage assembly 46 also includes a second link 50 having an outer end 58 pivotally interconnected with the movable guard 42, also at a fixed location thereon. The opposite intermediate ends of the first link 48 and the second link 50 are pivotally interconnected with each other and with an intermediate rotatable pivot and roller assembly 52. The roller assembly 52 is adapted to engage a cam surface 54 formed on the drive housing assembly 36 (and thus fixed relative to the fixed upper guard) for purposes of controlling the closing and opening movement of the movable guard 42 as the drive housing 36 and the blade 18 are raised and lowered, respectively, out of and into cutting engagement with the workpiece 13. The shape and position of the cam surface 54 are carefully chosen in order to determine and select the amount and rate of opening movement of the lower guard 42. These raised and lowered positions are diagrammatically illustrated in Figures 10a and 10c, respectively. Because the intermediate roller assembly 52 is free to move, along with the intermediate ends of the first link 48 and the second link 50, along the cam surface 54, the location of the intermediate roller assembly 52 is not fixed or restrained with respect to either the fixed upper guard 40 (which is fixed with respect to the drive assembly 36) or the movable lower guard 42. Thus, primarily for ease of blade changing, replacement or maintenance, the movable lower guard 42 can be manually pivoted by the user about the arbor shaft axis 45 in an overriding manner, independent and irrespective of the pivotal position of the drive assembly 36 and the blade 18. Two examples of this independent overriding movement of the movable lower guard 42 are shown in Figure 10b, wherein the movable guard 42 has been pivoted to a maximum open position with the drive assembly 36 in its upward, "at rest" position, and in Figure 10d, wherein the movable guard 42 has been independently and overridingly pivoted about the arbor shaft axis 45 to a maximum open position with the blade 18 and the drive assembly 36 in their downward, workpiece-engaging position. In both of these overridingly and independently pivoted positions of the movable lower guard 42, the intermediate roller assembly 52, along with the intermediate ends of the first and second links 48 and 50, pivot upwardly out of contact with the cam surface 54. Referring primarily to Figures 5 through 9c, the linkage assembly 46 also preferably includes a return spring 70, which is preferably of the torsional coil spring variety shown in the drawings. The return spring 70 functions to resiliently and normally bias the movable lower guard 42 toward its "closed" position illustrated in Figures 1 through 4 and 10a. This return spring 70, along with the drive assembly return spring 37 shown in Figure 5, thus serve to resiliently bias both the movable lower guard 42 and the entire drive assembly 36 to the "at-rest" position shown in Figures 1 through 4 and 10a. Because the preferred return spring 70 is a torsional coil spring, it radially expands and contracts relative to the arbor shaft axis 45 as the movable guard 42 is pivoted about a lower guard axis 47 (see Figures 8, 9a-c, and 10a-d) between its "closed" and "open" positions, respectively. The drive assembly 36 is also preferably equipped with a return spring enclosure 72, shown in Figures 6 and 8 and diagrammatically illustrated in Figures 9a through 9c. The return spring enclosure 72 is radially offset with respect to the pivot axis 47 of the movable lower guard 42 in a generally upward direction, away from the saw's base assembly 12 and the workpiece 13. The offset return spring enclosure 72 is mounted on, or interconnected with, a drive assembly hub portion 74 (shown in Figure 6) of the drive assembly 36 and is thus fixed with respect to the fixed upper guard 40. The return spring 70 includes a fixed spring leg 76 (fixed relative to the spring enclosure 72 by way of its engagement with an opening 80 in the spring enclosure) and a movable spring leg 78 (movable with the movable lower guard 42 by way of its engagement with an opening 82 in the movable lower guard) at its ends. The return spring legs 76 and 78 are carefully placed and configured to prevent extreme bending of these legs as the spring expands and contracts. As is diagrammatically illustrated in Figures 9a through 9c, the radially offset configuration of the return spring enclosure 72 allows the return spring 70 to radially expand and contract to a greater degree in directions away from the saw's base assembly 12, and thus away from the workpiece 13, than in directions toward the workpiece 13. This feature minimises interference with the workpiece 13 during cutting operations and thus maximises the cutting depth capacity of the compound miter saw 10. Preferably, the spring enclosure 72 and the return spring 70 are placed inside the blade cavity rather than outside, to allow for more gearbox space. This further provides more space for the return spring 70 itself, which significantly extends spring life. Figure 9a diagrammatically depicts the movable lower guard 42 in its "closed" position, with the return spring 70 in its preloaded, maximum radially-expanded condition. Figure 9b illustrates the position of the movable lower guard 42 and the degree of radial expansion of the return spring 70 when the drive assembly 36 is lowered to a workpiece-engaging or cutting position. Figure 9c illustrates the position of the movable lower guard 42 and the minimal radially expansion condition of the return spring 70 when the movable lower guard 42 is manually and overridingly opened to its maximum extent. Referring to Figures 11 through 13, the drive assembly 36 of the compound miter saw 10 also preferably includes an arbor shaft cover 66 pivotally interconnected at one end by way of a pivot fastener 67 to the fixed upper guard 40. The opposite end of the arbor shaft cover 66 is releasably secured to the fixed upper guard 40 by way of a threaded retaining fastener 69 that passes through a slotted opening 68 in the arbor shaft cover 66. This allows the cover 66 to be selectively released and pivoted upwardly about the pivot fastener 67 relative to the fixed upper guard 40 to an "open" position, thus completely exposing the arbor shaft fastener 64 and allowing removal, replacement or maintenance of the blade 18. When the arbor shaft cover 66 is pivoted back to its "closed" position shown in Figure 11, it preferably covers at least one-half of the diameter of the arbor shaft 44 and prevents the arbor shaft fastener 64 from vibrating loose and falling free of the arbor shaft 44. Referring to Figures 13a and 13b, the arbor cover retaining fastener 69 can also optionally be configured to extend axially inside the fixed upper guard 40 to a position axially spaced from the blade 18 at a radial location well inboard of the cutting teeth of the blade 18 when the retaining fastener 69 is threadably tightened on the fixed guard 40, as is diagrammatically shown in Figure 13a. This configuration allows the retaining fastener 69 to act as a blade caliper, in conjunction with another blade caliper 71, while still allowing the fastener 69 to perform its arbor cover retaining function. The blade caliper 71 is fixed on the upper guard 40 and axially spaced from the opposite side of the blade 18, generally at the same inboard radial position as the retaining fastener/caliper 69. These calipers serve to substantially prevent, or at least minimise, damage to the fixed upper guard 40 in the event of a bent or deflected blade 18. As shown in Figure 13b, the retaining fastener 69 can be loosened to release the arbor shaft cover 66 for pivoting to its open position. It is preferable to provide a tab 66a on the arbor shaft cover 66. The tab 66a forces a user to withdraw the fastener 69 a sufficient amount to allow the arbor shaft cover 66 to be pivoted and clear the fastener 69. In addition, by withdrawing the fastener 69, the caliper is effectively disengaged, allowing for removal of the blade 18. The saw 10 can optionally be equipped with a hold-down member or strap 90, illustrated in Figures 14a and 14b. The hold-down strap 90 is pivotally interconnected with the base assembly 12, preferably on the turntable assembly 14. The hold-down strap 90 can be pivoted upwardly, as shown in Figure 14a, so that its hooked end 92 can be releasably engaged with the drive assembly 36, preferably at the pivot fastener 67 for the arbor cover 66, thus holding the drive assembly 36 in its downwardly pivoted position and preventing the drive assembly 36 (and thus the support arms 34 and the blade 18) from being slid completely inwardly toward the fence assembly 26 (Figures 1 through 4). When not required for saw storage, the hold-down strap 90 can be pivoted to its own storage position shown in Figure 14b, where it is out of the way during workpiece cutting or shaping operations. The strap 90 can be releasably retained in its storage position using any of a wide variety of well-known releasable retention arrangements. However, one arrangement currently contemplated is a strap 90 that is resiliently deflectable laterally, with the strap having a resilient bias in the rightward lateral direction as viewed in Figures 14a and 14b from the user's normal position. Thus, when it is desired to move the strap 90 from its use position shown in Figure 14a to its storage position shown in Figure 14b, the user merely deflects the resilient strap 90 leftwardly (against its rightward bias) so that the strap 90 can be pivoted downwardly, clear of a retention tab 94 on the turntable assembly 14. Once the strap 90 is pivoted downwardly past the retention tab 94, it can then be released by the user to resiliently deflect rightwardly to be releasably retained beneath the retention tab 94, as shown in Figure 14b. As mentioned above, other common releasable retention schemes can also alternatively be employed. Another feature of the invention is the back latch mechanism 300. Referring to Figures 4 and 17, there are two main components to the latch mechanism 300: the latch post 301 and latch hook 302. Preferably the latch post 301 will be placed on a stationary part, such as support housing 16. Conversely the latch hook 302 can be placed on a moving part, such as the drive assembly 34. Accordingly, the latch hook 302 would be pivotally attached to the drive assembly 34 with a pin 303. In addition, the latch hook 302 may be spring loaded via sprig 304 so that the hook 302 is biased towards clockwise rotation. A stop 305 would maintain the latch hook 302 in the proper position. Persons skilled in the art will recognise other alternative locations for these elements, as well as equivalent means. As shown in Figure 17a, when the drive assembly 34 is near the support housing 16, the drive assembly 34 can be latched via the engagement of the latch post 301 and the latch hook 302. A user needs only to move the drive assembly 34 back in order to engage the latch post 301. Accordingly, the latch post 301 would ride along an inclined ramp 302a on the hook 302, lifting the hook 302 until the latch post 301 is cleared. The latch hook 302 then rotates in a clockwise direction, "hooking" the latch post 301. The back latch mechanism 300 prevents a user from sliding the drive assembly 34 forward. In order to unlatch the drive assembly 34, a user needs only to pivot the drive assembly 34 downwardly slightly. As shown in Figure 17b, the latch hook 302 rotates with the drive assembly 34, leaving enough clearance to bypass the latch post 301 when the drive assembly 34 is slid forward. Another feature of the present invention is the blade guard lock mechanism 200. Basically, the lock mechanism 200 engages the blade guard assembly 20 so that the drive assembly 34 cannot be pivoted downwardly until the lock mechanism 200 is disengaged. As shown in Figures 2, 3, 4, and 15, the lock mechanism 200 includes an engaging portion 201, which preferably engages the movable guard 42, a paddle 202 for engaging and disengaging the lock mechanism 200, and a body 203 connecting the paddle 202 with the engaging portion 201. In addition, the paddle 202 may include an extension 204, which in turn includes a pin 205 mating with a handle extension 206. Accordingly, the lock mechanism 200 pivots about pin 205. As mentioned above, when the engaging portion 201 is engaged to the movable guard 42, the drive assembly 34 cannot be pivoted downwardly until the lock mechanism 200 is disengaged. In order to disengage the lock mechanism 200, a user would push the paddle 202 to pivot the lock mechanism 200 about pin 205 and out of engagement, allowing downward pivoting of the drive assembly 34. Preferably the lock mechanism 200 will be designed so that the user must push the paddle 202 in order to press the switch 210. It is also preferable to provide a spring 207 to bias the lock mechanism 200 towards an engaging position. Persons skilled in the art will recognise that the combination of the lock mechanism 200 with the back latch mechanism 300 will force a user to disengage the lock mechanism 200 in order to slide the drive assembly 34 forward. This is because the drive assembly 34 cannot be unlatched and slid forward unless it is pivoted downwardly. Further, the drive assembly 34 cannot be pivoted downwardly unless the lock mechanism 200 is disengaged. Persons skilled in the art will recognise that this result can be achieved with a minimum number of elements and thus lower manufacturing costs. Another feature of the invention is the motor 22. Typically, the motor 22 has been a universal motor, which may also employ a brake to shorten the coast downtime of the rotatably mounted saw blade. This is accomplished by reconnecting the universal motor into a short circuited generator. This is sometimes referred to as "regenerative" braking or "dynamic" braking. A separate circuit operated by a second contact of the switch engages and disengages the brake. Unfortunately, the optimum brush timing, or "brush lead" is different for a motor and a generator. Thus, braking the motor in the manner described above increases wear and tear on the motor brush and commutator. In addition, the braking action of a universal motor decreases sharply as the motor slows down, extending the total stopping time. A switched reluctance motor is used instead as the motor 22. Switched reluctance motors rely upon semiconductor switches and complex logic for operation. Such motors are also capable of braking, again relying upon those same semiconductor switches and logic. In addition, switched reluctance motors can be controlled to provide braking down to near zero speed, thus reducing total stopping time. As shown in Figure 16, a schematic control circuit is illustrated showing the switched reluctance motor 22 electrically connected to the electronic motor drive 211 and operated by the switch 210 in the handle 24 of the saw 10. As in prior art saws, the switch 210 may include first and second contacts. Thus, upon depression of the switch 210, the switched reluctance motor 22 is energised to drive the saw blade. Upon release of the switch 210, the second contact can be electrically connected to the electronic motor drive 211 to brake the switched reluctance motor 22. Alternatively, the electronic motor drive 211 can be configured to sense that the switch 210 is open, in other words, released, and then automatically brake the switched reluctance motor 22. Thus, the electronic motor drive 211 can be configured in any desired manner to work in conjunction with the switch 210 to brake the switched reluctance motor 22. Other variations are possible including the addition of a variable speed control to the switched reluctance motor 22. Another variation can include a soft start, i.e., relatively slow ramp up of motor speed, in the electronic motor drive 211 in order to reduce the strain on a gear reduction drive as well as reduce the starting in rush current to the switched reluctance motor 22. This is an advantage when long extension cords are used. From the foregoing, it will now be appreciated that the saw with switched reluctance motor eliminates wear and tear on brushes and commutators as in prior art universal motors as well as eliminates regenerative or dynamic braking associated with the universal motor. Wear and tear is substantially eliminated because switched reluctance motors rely upon semiconductor switches and complex logic to operate. Because switched reluctance motors are capable of braking, as a result of the semiconductor switches and logic, they can be controlled to provide braking down to near zero speed, thus reducing the total stopping time. The foregoing discussion discloses and describes merely exemplary embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognise from such discussion, and from the accompanying drawings and claims, that various changes, modifications, and variations can be made therein without departing from the scope of the claims.

Claims: A cutting device for performing cutting operations on a workpiece, said cutting device comprising: a base assembly (12) for receiving the workpiece; a support assembly (32) interconnected with said base assembly; a drive assembly including a motor (22), an arbor shaft rotatable about an arbor axis (45), and a cutting tool (18) driven by said motor about said arbor shaft, said drive assembly being pivotally interconnected with said support for selective pivotal movement of said motor and said cutting tool relative to said support assembly between an at-rest position wherein said cutting tool is out of engagement with the workpiece when the workpiece is on said base and an operational position wherein said cutting tool is in a cutting engagement with the workpiece when the workpiece is on said base; a guard assembly (20) including a fixed guard (40) partially surrounding a cutting periphery of said cutting tool, a movable guard(42), said fixed guard being fixedly interconnected with said drive assembly, and said movable guard being pivotally interconnected with said drive assembly for pivotal movement about said arbor shaft between a closed position surrounding a predetermined portion of the cutting periphery of said cutting tool and an open position covering a lesser portion of the cutting periphery of said cutting tool than when in said closed position, and a linkage assembly (46) for drivingly moving said movable guard between said closed and said open positions as said drive assembly is moved between said at-rest and said operational positions, respectively; and a locking mechanism (200) for preventing pivoting downwardly the drive assembly; characterised in that said linkage assembly comprises: a first link (48) having an inner end (56) pivotally interconnected with said support at a fixed location thereon and an opposite intermediate end; a second link (50) having an outer end (58) pivotally interconnected with said movable guard and an opposite intermediate end pivotally interconnected with said intermediate end of said first link for pivotal movement relative thereto about an intermediate linkage axis; an intermediate roller (52) rotatably interconnected with said intermediate ends of said first and second links for rotation about said intermediate linkage axis; and a cam surface (54) fixed relative to said drive assembly and said fixed guard and engageable by said roller for rotation of said roller thereon. A cutting device according to claim 1, wherein the locking mechanism comprises an engaging portion (201) movable between a first position engaging the movable guard and a second position not engaging the movable guard, so that the drive assembly cannot be pivoted downwardly when the engaging portion is in the first position. A cutting device according to claim 2, wherein the locking mechanism further comprises a paddle (202) connected to the engaging portion for moving engaging portion between the first and second positions. A cutting device according to any one of the preceding claims, wherein said movable guard is selectively pivotally moveable for overriding pivotal movement about said arbor shaft irrespective of the pivotal position of said drive assembly relative to said support assembly. A cutting device according to claim 4, wherein said roller moves out of engagement with said cam surface during said overriding pivotal movement of said movable guard. A cutting device according to any one of the preceding claims, wherein said linkage assembly further includes a return spring (70) resiliently biasing said moveable guard toward said closed position. A cutting device according to claim 6, wherein said return spring is a torsional coil spring surrounding said arbor shaft, said torsional coil spring having one end interconnected with said drive assembly at a fixed location thereon and an opposite end interconnected with said movable guard at a fixed location thereon, said torsional coil spring radially expanding when said drive assembly is moved toward said operational position and radially contracting when said drive assembly is moved away from said operational position. A cutting device according to claim 1, wherein said cutting device is a miter saw. A cutting device according to claim 1, wherein said cutting device is a compound miter saw.

Inventors: MEREDITH DARYL, O'BANION MICHAEL L, PRICE SCOTT, STUMPF WILLIAM R, MEREDITH, DARYL, O'BANION, MICHAEL L., PRICE, SCOTT, STUMPF, WILLIAM R.
Applicants: BLACK & DECKER INC, BLACK & DECKER INC.
Application year: 1998
Main classification: B27G19
IPC codes: B27G19