Brake positioning system

A saw is disclosed having a detection system adapted to detect a dangerous condition between a person and a saw blade, and a brake adapted to stop the saw blade in response to detection of the dangerous condition. The saw further includes a brake positioning system that allows the brake to be positioned in at least two different operable positions to accommodate at least two different blade diameters. The saw may include a system to detect brake-to-blade spacing.

FIELD

The present invention relates to safety braking systems and more particularly to a brake positioning system for use in a fast acting safety brake system.

BACKGROUND

Various active safety systems have been developed to prevent injury to a user if they approach or come into contact with a dangerous portion of a machine. Such systems typically include two components: a detection portion and a braking portion. U.S. Pat. Nos. 3,785,230 and 4,026,177 to Lokey describe one such system. The system of Lokey uses a detection system that detects dangerous proximity of a part of a user's body. The system relies on a radio-frequency proximity detection. When the detection system detects a dangerous condition, a solenoid is triggered to shift a brake into engagement with the blade. Because the system of Lokey does not wait for contact to occur, the relatively low brake actuation speed provided by a direct-acting solenoid may be adequate to prevent injury. However, in a system that relies on contact detection, the braking time must be minimized. Even in proximity-based systems, it is beneficial to reduce braking time to minimize the chance of injury.

In a system that utilizes a brake to stop the machine, the spacing between the brake and the portion of the machine to be braked—typically a cutter or saw blade—can lead to significant delays in brake action. For instance, a solenoid may supply a few pounds of Rio force over an eighth of an inch. With a relatively light brake of 150 g, a solenoid capable of generating 10 pounds of force takes five milliseconds to move the brake an eighth of an inch. Thus, it is important that the brake be located as close as possible to the portion of the machine to be stopped. However, where the brake contacts the blade directly, the position of the brake may need to be adjustable to accommodate variations in blade size.

DETAILED DESCRIPTION

A machine that may incorporate a brake positioning system according to the present invention is shown schematically in FIG.1and indicated generally at10. Machine10may be any of a variety of different machines adapted for cutting workpieces, such as wood, including a table saw, miter saw (chop saw), radial arm saw, circular saw, band saw, jointer, planer, etc. Machine10includes an operative structure12having a cutting tool14and a motor assembly16adapted to drive the cutting tool. Machine10also includes a safety system18configured to minimize the potential of a serious injury to a person using machine10. Safety system18is adapted to detect the occurrence of one or more dangerous conditions during use of machine10. If such a dangerous condition is detected, safety system18is adapted to engage operative structure12to limit any injury to the user caused by the dangerous condition.

Machine10also includes a suitable power source20to provide power to operative structure12and safety system18. Power source20may be an external power source such as line current, or an internal power source such as a battery. Alternatively, power source20may include a combination of both external and internal power sources. Furthermore, power source20may include two or more separate power sources, each adapted to power different portions of machine10.

It will be appreciated that operative structure12may take any one of many different forms, depending on the type of machine10. For example, operative structure12may include a stationary housing configured to support motor assembly16in driving engagement with cutting tool14. Alternatively, operative structure12may include a movable structure configured to carry cutting tool14between multiple operating positions. As a further alternative, operative structure12may include one or more transport mechanisms adapted to convey a workpiece toward and/or away from cutting tool14.

Motor assembly16includes one or more motors adapted to drive cutting tool14. The motors may be either directly or indirectly coupled to the cutting tool, and may also be adapted to drive workpiece transport mechanisms. Cutting tool14typically includes one or more blades or other suitable cutting implements that are adapted to cut or remove portions from the workpieces. The particular form of cutting tool14will vary depending upon the various embodiments of machine10. For example, in table saws, miter saws, circular saws and radial arm saws, cutting tool14will typically include one or more circular rotating blades having a plurality of teeth disposed along the perimetrical edge of the blade. For a jointer or planer, the cutting tool typically includes a plurality of radially spaced-apart blades. For a band saw, the cutting tool includes an elongate, circuitous tooth-edged band.

Safety system18includes a detection subsystem22, a reaction subsystem24and a control subsystem26. Control subsystem26may be adapted to receive inputs from a variety of sources including detection subsystem22, reaction subsystem24, operative structure12and motor assembly16. The control subsystem may also include one or more sensors adapted to monitor selected parameters of machine10. In addition, control subsystem26typically includes one or more instruments operable by a user to control the machine. The control subsystem is configured to control machine10in response to the inputs it receives.

Detection subsystem22is configured to detect one or more dangerous, or triggering, conditions during use of machine10. For example, the detection subsystem may be configured to detect that a portion of the user's body is dangerously close to, or in contact with, a portion of cutting tool14. As another example, the detection subsystem may be configured to detect the rapid movement of a workpiece due to kickback by the cutting tool, as is described in U.S. Provisional Patent Application Ser. No. 60/182,866, the disclosure of which is herein incorporated by reference. In some embodiments, detection subsystem22may inform control subsystem26of the dangerous condition, which then activates reaction subsystem24. In other embodiments, the detection subsystem may be adapted to activate the reaction subsystem directly.

Once activated in response to a dangerous condition, reaction subsystem24is configured to engage operative structure12quickly to prevent serious injury to the user. It will be appreciated that the particular action to be taken by reaction subsystem24will vary depending on the type of machine10and/or the dangerous condition that is detected. For example, reaction subsystem24may be configured to do one or more of the following: stop the movement of cutting tool14, disconnect motor assembly16from power source20, place a barrier between the cutting tool and the user, or retract the cutting tool from its operating position, etc. The reaction subsystem may be configured to take a combination of steps to protect the user from serious injury. Placement of a barrier between the cutting tool and teeth is described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,206, entitled “Cutting Tool Safety System,” filed Aug. 14, 2000 by SD3, LLC, the disclosure of which is herein incorporated by reference. Retraction of the cutting tool from its operating position is described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,089, entitled “Retraction System For Use In Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, the disclosure of which is herein incorporated by reference.

The configuration of reaction subsystem24typically will vary depending on which action(s) are taken. In the exemplary embodiment depicted inFIG. 1, reaction subsystem24is configured to stop the movement of cutting tool14and includes a brake mechanism28, a biasing mechanism30, a restraining mechanism32, and a release mechanism34. Brake mechanism28is adapted to engage operative structure12under the urging of biasing mechanism30. During normal operation of machine10, restraining mechanism32holds the brake mechanism out of engagement with the operative structure. However, upon receipt of an activation signal by reaction subsystem24, the brake mechanism is released from the restraining mechanism by release mechanism34, whereupon, the brake mechanism quickly engages at least a portion of the operative structure to bring the cutting tool to a stop.

It will be appreciated by those of skill in the art that the exemplary embodiment depicted in FIG.1and described above may be implemented in a variety of ways depending on the type and configuration of operative structure12. Turning attention toFIG. 2, one example of the many possible implementations of safety system18is shown. System18is configured to engage an operative structure having a cutting tool in the form of a circular blade40mounted on a rotating shaft or arbor42. Blade40includes a plurality of cutting teeth (not shown) disposed around the outer edge of the blade. As described in more detail below, braking mechanism28is adapted to engage the teeth of blade40and stop the rotation of the blade. U.S. Provisional Patent Application Ser. No. 60/225,210, entitled “Translation Stop For Use In Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, the disclosure of which is herein incorporated by reference, describes other systems for stopping the movement of the cutting tool. U.S. Provisional Patent Application Ser. No. 60/225,058, entitled “Table Saw With Improved Safety System,” filed Aug. 14, 2000 by SD3, LLC, and U.S. Provisional Patent Application Ser. No. 60/225,057, entitled “Miter Saw With Improved Safety System,” filed Aug. 14, 2000 by SD3, LLC, the disclosures of which are herein incorporated by reference, describe safety system18in the context of particular types of machines10.

In the exemplary implementation, detection subsystem22is adapted to detect the dangerous condition of the user coming into contact with blade40. The detection subsystem includes a sensor assembly, such as contact detection plates44and46, capacitively coupled to blade40to detect any contact between the user's body and the blade. Typically, the blade, or some larger portion of cutting tool14is electrically isolated from the remainder of machine10. Alternatively, detection subsystem22may include a different sensor assembly configured to detect contact in other ways, such as optically, resistively, etc. In any event, the detection subsystem is adapted to transmit a signal to control subsystem26when contact between the user and the blade is detected. Various exemplary embodiments and implementations of detection subsystem22are described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,200, entitled “Contact Detection System For Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, and U.S. Provisional Patent Application Ser. No. 60/225,211, entitled “Apparatus And Method For Detecting Dangerous Conditions In Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, the disclosures of which are herein incorporated by reference.

Control subsystem26includes one or more instruments48that are operable by a user to control the motion of blade40. Instruments48may include start/stop switches, speed controls, direction controls, etc. Control subsystem26also includes a logic controller50connected to receive the user's inputs via instruments48. Logic controller50is also connected to receive a contact detection signal from detection subsystem22. Further, the logic controller may be configured to receive inputs from other sources (not shown) such as blade motion sensors, workpiece sensors, etc. In any event, the logic controller is configured to control operative structure12in response to the user's inputs through instruments48. However, upon receipt of a contact detection signal from detection subsystem22, the logic controller overrides the control inputs from the user and activates reaction subsystem24to stop the motion of the blade. Various exemplary embodiments and implementations of control subsystem26are described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,059, entitled “Logic Control For Fast Acting Safety System,” filed Aug. 14, 2000 by SD3, LLC, and U.S. Provisional Patent Application Ser. No. 60/225,094, entitled “Motion Detecting System For Use In Safety System For Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, the disclosures of which are herein incorporated by reference.

In the exemplary implementation, brake mechanism28includes a pawl60mounted adjacent the edge of blade40and selectively moveable to engage and grip the teeth of the blade. Pawl60may be constructed of any suitable material adapted to engage and stop the blade. As one example, the pawl may be constructed of a relatively high strength thermoplastic material such as polycarbonate, ultrahigh molecular weight polyethylene (UHMW) or Acrylonitrile Butadiene Styrene (ABS), etc., or a metal such as aluminum, etc. It will be appreciated that the construction of pawl60will vary depending on the configuration of blade40. In any event, the pawl is urged into the blade by a biasing mechanism in the form of a spring66. In the illustrative embodiment shown inFIG. 2, pawl60is pivoted into the teeth of blade40. It should be understood that sliding or rotary movement of pawl60might also be used. The spring is adapted to urge pawl60into the teeth of the blade with sufficient force to grip the blade and quickly bring it to a stop.

The pawl is held away from the edge of the blade by a restraining mechanism in the form of a fusible member70. The fusible member is constructed of a suitable material adapted to restrain the pawl against the bias of spring66, and also adapted to melt under a determined electrical current density. Examples of suitable materials for fusible member70include NiChrome wire, stainless steel wire, etc. The fusible member is connected between the pawl and a contact mount72. Preferably, fusible member70holds the pawl relatively close to the edge of the blade to reduce the distance the pawl must travel to engage the blade. Positioning the pawl relatively close to the edge of the blade reduces the time required for the pawl to engage and stop the blade. Typically, the pawl is held approximately {fraction (1/32)}-inch to ¼-inch from the edge of the blade by fusible member70, however other pawl-to-blade spacings may also be used within the scope of the invention.

Pawl60is released from its unactuated, or cocked, position to engage blade40by a release mechanism in the form of a firing subsystem76. The firing subsystem is coupled to contact mount72, and is configured to melt fusible member70by passing a surge of electrical current through the fusible member. Firing subsystem76is coupled to logic controller50and activated by a signal from the logic controller. When the logic controller receives a contact detection signal from detection subsystem22, the logic controller sends an activation signal to firing subsystem76, which melts fusible member70, thereby releasing the pawl to stop the blade. Various exemplary embodiments and implementations of reaction subsystem24are described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,056, entitled “Firing Subsystem For Use In Fast Acting Safety System,” filed Aug. 14, 2000 by SD3, LLC, U.S. Provisional Patent Application Ser. No. 60/225,170, entitled “Spring-Biased Brake Mechanism for Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, and U.S. Provisional Patent Application Ser. No. 60/225,169, entitled “Brake Mechanism For Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, the disclosures of which are herein incorporated by reference.

It will be appreciated that activation of the brake mechanism will require the replacement of one or more portions of safety system18. For example, pawl60and fusible member70typically must be replaced before the safety system is ready to be used again. Thus, it may be desirable to construct one or more portions of safety system18in a cartridge that can be easily replaced. For example, in the exemplary implementation depicted inFIG. 2, safety system18includes a replaceable cartridge80having a housing82. Pawl60, spring66, fusible member70and contact mount72are all mounted within housing82. Alternatively, other portions of safety system18may be mounted within the housing. In any event, after the reaction system has been activated, the safety system can be reset by replacing cartridge80. The portions of safety system18not mounted within the cartridge may be replaced separately or reused as appropriate. Various exemplary embodiments and implementations of a safety system using a replaceable cartridge are described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,201, entitled “Replaceable Brake Mechanism For Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, the disclosure of which is herein incorporated by reference.

While one particular implementation of safety system18has been described, it will be appreciated that many variations and modifications are possible within the scope of the invention. Many such variations and modifications are described in U.S. Provisional Patent Application Ser. Nos. 60/182,866 and 60/157,340, the disclosures of which are herein incorporated by reference.

A brake positioning system according to the present invention is shown generally at800in FIG.3. Cartridge80and brake pawl60are typically pivotally mounted on a large pin802. The cartridge and pawl are fixed together until the brake is fired, at which time the brake pawl is shoved rapidly into the blade. The motion of the blade and geometry of the pawl then cause the blade to drive deeply into the pawl creating tremendous deceleration. Pin802is sufficiently large, typically 0.75 inches, to absorb the impact of deceleration without damage. The large diameter of pin802also reduces the chance that it will fracture brake pawl60during braking. The pivotal mounting of the cartridge on the pin permits the spacing between the blade and the face of the brake pawl to be adjusted by rotating the cartridge around the pin. The brake position system serves to establish and maintain the proper spacing between the face of the pawl and the perimeter of blade40.

In its simplest form, brake positioning system800incorporates a fixed pin804to position cartridge80, and thereby brake pawl60. This arrangement is generally sufficient where the size of the blade is known and sufficiently fixed for all blades that might be used. Pin804is arranged parallel to pin802to allow cartridge80to be slid onto both pins simultaneously. A flexible snap clip806snaps over the edge of cartridge80to retain it on the pins. When the cartridge is to be removed, the clip is lifted away from the cartridge, and the cartridge is slipped off of the pins. A clearance pin808is preferably mounted at a fixed radius from the arbor axis, 5{fraction (1/16)}thinches for instance, to insure that no larger blade than will clear the pawl will fit on the saw. The clearance pin is preferably located at a just slightly smaller radial position from the arbor than the nearest portion of the pawl so that the blade will contact the pin prior to contacting the pawl. Alternatively, the pin may take the form of a curved arc that is sufficiently large to insure that at least one tooth of the blade will engage it.

An adjustable brake positioning system800is shown inFIGS. 4-6. Brake positioning system800includes a plurality of positioning teeth812formed on the back of cartridge80. A corresponding plurality of positioning teeth814are formed on a cartridge mounting surface816. The teeth preferably have a pitch of approximately {fraction (1/32)}nd to ¼thof an inch. The teeth are spaced so that relatively small adjustments can be made by selecting where to engage the teeth. A curved wall818is formed along part of the inside front edge of the cartridge. The curved wall818is positioned to engage the perimeter of the blade just prior to the positioning teeth engaging each other as the cartridge is slipped onto pin802. This insures that the pawl will be spaced back from the blade by at least the distance the wall projects forward from the pawl—typically {fraction (1/16)}thto ⅛thinch. Once the positioning teeth are engaged, the rotational position of the cartridge is fixed. The cartridge is then slid the rest of the way onto the pin. Snap clip806retains the cartridge against mounting surface and in proper position. A tab820formed on the edge of the cartridge extends over the blade. The tab blocks the blade from being removed unless the cartridge is partially disengaged and rotated back away from the blade. Thus, the tab insures that the blade cannot be removed and replaced with a new blade without resetting the position of the cartridge. It can be seen that by making the cartridge pivotal on pin802, adjustable positioning of the brake pawl relative to the blade is simplified.

Because of the importance of establishing correct pawl-to-blade spacing, it may be desirable to incorporate a spacing detection system to insure correct spacing. One example of such a system is shown at824in FIG.7. System824includes an electrode826located on the face of the pawl adjacent the blade. As described in U.S. Provisional Patent Application Ser. No. 60/225,200, titled “Contact Detection System for Power Equipment,” and U.S. Provisional Patent Application Ser. No. 60/225,211, titled “Apparatus and Method for Detecting Dangerous Conditions in Power Equipment,” both filed Aug. 14, 2000, in one contact detection system suitable for use with the present invention, an electrical signal is applied to the blade via a drive electrode. This signal can be picked up by electrode826and monitored to ensure that it has an amplitude in a predetermined range. In particular, the amplitude detected by electrode826will fall off rapidly with distance from the blade. Therefore, by monitoring the detected amplitude, proper spacing can be verified. The system preferably deactivates or prevents initial actuation of the machine if the detected spacing is outside normal range. The user is then signaled to make appropriate adjustment. Electrode826may take many forms, including capacitive plates, optical sensors, magnetic sensors, etc.

An alternative brake positioning system800is shown in FIG.8. The position system ofFIG. 8utilizes a snap catch830with a rib832facing the cartridge. The catch is mounted to cartridge support surface816and is biased to push against the cartridge. The end face of the cartridge includes a groove834adapted to receive rib832. In use, the cartridge is slipped over pin802while rotated back from the blade. Once the cartridge is fully installed on the pin, it is rotated forward until rib832snaps into groove834. A small ledge836projects over the edge of cartridge80when the rib is engaged in the groove to prevent the cartridge from vibrating off along the axis of the pin. Once the cartridge is fired, the user can lift tab838to disengage the rib and allow the cartridge to rotate back. The backward rotation can be used to release any remaining pressure from the actuation spring, if any, in the cartridge.

FIG. 9shows another brake positioning system800. In the system ofFIG. 9, cartridge80includes a recess850formed on one side. A spring latch852is positioned to engage recess850as cartridge80is rotated back away from the blade. The latch is positioned to locate the face of the pawl approximately ⅛thof an inch away from the perimeter of the blade, although different spacing could of course be used. The user can remove the cartridge by lifting the latch, rotating the cartridge forward until it clears the latch and then sliding the cartridge off pin802. As described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,201, titled “Replaceable Brake Mechanism for Power Equipment,” filed Aug. 14, 2000, when the cartridge is fired, the pawl will normally be somewhat embedded on the blade and biased toward the blade by a spring66. A release pin756is removable to release the back of the spring and remove the biasing pressure. This allows the pawl to be loosened from the blade more easily and eliminates the pressure on the blade that would otherwise make removal of the blade more difficult.

Logic controller50may also be configured to monitor the pawl-to-blade spacing. Many cutting tools such as saw blades do not have precisely uniform dimensions. As a result, when a new blade is installed on a saw, for example, the pawl may no longer be correctly spaced from the blade. An incorrectly positioned pawl may slow the stopping speed of the pawl or prevent the pawl from stopping the blade. Therefore, to ensure the blade is stopped with uniform braking speed, it may be necessary to adjust the position of the pawl whenever a blade is replaced. Configuring logic controller50to detect incorrect blade-to-pawl spacing, as described above and as described in U.S. Provisional Patent Application Ser. No. 60/225,059, entitled “Logic Control For Fast Acting Safety System,” provides an additional level of assurance that a user is protected against accidental contact with the blade.

It will be appreciated that there are many ways in which incorrect spacing between blade40and pawl60may be detected. One such way is described above in connection withFIGS. 5 and 7. As another example,FIG. 10illustrates a pawl945having a capacitive system for detecting correct pawl spacing. Similar to pawl40shown inFIG. 2, pawl945may include a portion946that is beveled or otherwise shaped to quickly and completely engage the teeth of a cutting tool. In addition, pawl945includes a pair of generally parallel, spaced-apart arms947which extend beyond portion946. Arms947are disposed to extend on either side of the blade, without touching the blade, when the pawl is in place adjacent the blade. Each arm includes a capacitor plate electrode826disposed on the inside surface of the arm adjacent the blade. Conductive leads949run from each plate826to suitable blade detector circuitry.

Capacitor plates826are positioned on arms947such that, when the pawl spacing is within a desired range, the blade extends between the two capacitor plates. It will be appreciated that the capacitance across plates826will vary depending on whether the blade is positioned between the sensors. The blade detector circuitry is configured to drive an electrical signal through conductive leads949and to detect changes in the capacitance across the plates. Suitable circuitry that may be used with pawl945is well known to those of skill in the art. One exemplary pawl-to-blade spacing detection circuit was discussed above and is shown in FIG.7. An electrical signal applied to the blade can be picked up by either or both of plates826and monitored to insure that the signal has an amplitude in a predetermined range. By monitoring the detected amplitude, proper spacing can be verified. If the proper signal is not detected, a circuit, such as circuit824inFIG. 7, conveys an error signal to logic controller50, which prevents operation of machine10until proper pawl-to-blade spacing is detected. Other examples include circuits similar to the exemplary contact detection circuits described in U.S. Provisional Application Ser. No. 60/225,200 entitled “Contact Detection System for Power Equipment.”

Capacitor plates826can optionally be shaped to detect when the pawl is too close to the blade as well as not close enough. Alternatively, two pairs of capacitor plates may be positioned on the pawl: one pair to detect if the pawl is too close to the blade, and the other pair to detect if the pawl is too far from the blade. In any event, the detector circuitry is configured to transmit an error signal to logic controller50, which then takes appropriate action.

While exemplary automatic pawl spacing detection systems have been described above, it will be appreciated that there are many possible variations within the scope of the invention. For example, both capacitor plates may be positioned on the same side of the blade rather than on opposite sides. The plates and/or blade detection circuitry may be separate from the pawl. In the latter case, for example, the plates and detection circuitry may be mounted on a separate electronics board associated with the pawl. Alternatively, the plates may be replaced with one or more light-emitting diodes and detectors such that, when the pawl is properly positioned, the blade obstructs the optical path between the diodes and detectors. Other methods of detecting the proximity of the blade to the pawl are also possible. As a further option, plates826may function as charge plates44,46as well as pawl-spacing detectors. In addition, a plate may be mounted on beveled face of a pawl, such as on face946of the pawl shown in FIG.10. This plate can be used to detect the drive input signal used for contact detection. The amplitude of the signal detected at the plate will be inversely proportional to the space between the sensor and the teeth of the blade. If this signal does not have an amplitude over a given threshold, the system would interpret this as indicating that the pawl face is not close enough to the blade.

In embodiments where portions of safety system18are mounted in a replaceable cartridge80, the correct blade-to-pawl spacing may be detected by measuring the blade-to-cartridge spacing. For example, capacitor plates826may be placed on cartridge housing82rather than on a pawl itself.

INDUSTRIAL APPLICABILITY

The present invention is applicable to power equipment, and specifically to woodworking equipment such as table saws, miter saws, band saws, circular saws, jointers, etc.

It is believed that the disclosure set forth above encompasses multiple distinct inventions with independent utility. While each of these inventions has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein Rio are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the inventions includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. No single feature, function, element or property of the disclosed embodiments is essential to all of the disclosed inventions. Similarly, where the claims recite “a” or “a first” element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.