Abstract:
A power cutting tool, such as a table saw, comprising a sensing system for detecting certain conditions with respect to an exposed blade of the power cutting tool is disclosed. Several embodiments of the sensing system comprise at least one sensor located above the blade and positioned to (1) monitor one or more volume zones adjacent the blade, (2) detect when an object enters one or more of the zones, and (3) trigger a reaction system in response to the detection. Another embodiment uses an optical sensor to measure the height of objects approaching the blade to detect an increase in the height beyond a predetermined threshold. Still another embodiment uses an optical distance sensor to detect the occurrence of a work piece lifting from the table top which can indicate that a kick-back condition is imminent. The reaction system can be triggered when such a condition is detected.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to and hereby incorporates by reference U.S. provisional patent application Ser. No. 60/686,165, entitled “Overhead Sensing System,” filed 1 Jun. 2005, by W. H. Anderson et al. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention generally relates to sensing or detecting systems, and more particularly to sensing or detecting systems for power cutting tools. 
         [0003]    Detection or sensing systems have been developed for use with various kinds of manufacturing equipment and power tools. Such detection systems are operable to trigger some type of reaction mechanism when certain conditions are sensed or detected. For example, it is known to use a capacitive contact sensing system to detect contact between an operator and a blade of a table saw. In such systems, a signal is capacitively coupled to the blade and the signal on the blade is monitored to detect changes in the signal indicative of contact between the operator and the blade. Such capacitive sensing systems, however, are only practically able to detect contact between the operator and the blade. Such systems cannot practically detect the proximity of the operator to the blade. Detection systems that could detect when the operator or other object comes near the blade would be desirable. 
       SUMMARY OF THE INVENTION 
       [0004]    In one general aspect, the present invention is directed to a power cutting tool, such as a table saw, comprising a sensing system for detecting a condition with respect to an exposed, moveable blade of the power cutting tool. Several embodiments of the sensing system comprise at least one sensor located above the blade and positioned to (1) monitor one or more volume zones adjacent the blade, (2) detect when an object enters one or more of the zones, and (3) trigger a reaction system in response to the detection. 
         [0005]    According to various embodiments, the sensing system comprises an electrically conductive frame connected to the cutting platform (e.g., a table where the power cutting tool is a table saw). The frame may be spaced apart from and parallel to the cutting surface, and may surround at least a portion the blade. The sensing system also comprises an electrically conductive region (e.g. strip) on the cutting surface, facing the electrically conductive frame. When energized, a capacitive field extends between the electrically conductive strip and the electrically conductive frame. Changes in the field can indicate a condition relative to the blade, which can be used to trigger the reaction system. 
         [0006]    According to other embodiments, the sensing system comprises an optical energy detection system for detecting optical energy propagating between the frame and one or more detection zones on the cutting (or work) surface. The detection zone(s) may surround at least a portion of the blade. When two or more detection zones are used, the detection zones may be concentric around the blade. The detection zone may reflect light emitted from an emitter on the frame back to the frame for detection by a detector. Blockage of the optical energy path may indicate a condition relative to the blade, which can be used to trigger the reaction system. According to other embodiments, the detection zone(s) may comprise optical energy emitters or detectors. 
         [0007]    According to still other embodiments, the sensing system may comprise an optical energy emitter/detector pair positioned over the cutting surface of the cutting platform near the front of the blade. In this way, the height of objects near the front of the blade can be detected. An object that is too high may be used to trigger the reaction system. 
         [0008]    In another embodiment, an optical distance sensor is embedded in the cutting surface of the cutting tool near the back of the blade to detect the occurrence of a work piece lifting from the cutting surface, which can indicate that a kick-back condition is imminent. The reaction system can be triggered when such a condition is detected. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]    Various embodiments of the present invention are described herein by way of example in conjunction with the following figures, wherein: 
           [0010]      FIG. 1A  is a simplified perspective view of an embodiment of the present invention, particularly illustrating a capacitive overhead sensing system implemented in a table saw; 
           [0011]      FIG. 1B  is a simplified end view of the embodiment shown in  FIG. 1A ; 
           [0012]      FIG. 2A  is a simplified perspective view of another embodiment of the present invention, particularly illustrating an optical overhead sensing system implemented in a table saw; 
           [0013]      FIG. 2B  is a simplified end view of the embodiment shown in  FIG. 2A ; 
           [0014]      FIG. 3A  is a simplified perspective view of another embodiment of the present invention, particularly illustrating another optical overhead sensing system implemented in a table saw, wherein the system has more than one detection zone; 
           [0015]      FIG. 3B  is a simplified end view of the embodiment shown in  FIG. 3A ; 
           [0016]      FIG. 4A  is a simplified perspective view of another embodiment of the present invention, particularly illustrating another optical overhead sensing system implemented in a table saw; 
           [0017]      FIG. 4B  is a simplified end view of the embodiment shown in  FIG. 4A ; 
           [0018]      FIG. 5  is a simplified side view of another embodiment of the present invention, particularly illustrating an optical overhead sensing system implemented in a table saw, and particularly configured to measure the height of objects near the front of the blade; 
           [0019]      FIG. 6A  is a simplified perspective view of another embodiment of the present invention, particularly illustrating an optical sensing system implemented in a table saw, wherein the system is configured to detect a kickback condition; and 
           [0020]      FIG. 6B  is a simplified side view of the embodiment shown in  FIG. 6A . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The present invention is directed generally to a power cutting tool, such as a table saw, comprising a sensing system for detecting certain conditions with respect to the blade of the cutting tool. There are several embodiments disclosed herein that relate to overhead frame supports for sensing the presence of an object in close proximity to the rotating blade of a table saw. While the embodiments that are shown and described below are implemented in the environment of a table saw, it should be understood that they could also be implemented in other types of power cutting tools, such as miter saws, chop-saws, arm saws, band saws, etc. The use of an overhead frame structure enables accurate detection of the proximity of an object in the zones of detection. Other embodiments employ a structure mounted in the cutting surface of the power cutting tool in position to monitor the lifting of a work piece during cutting thereof by the table saw, with the lifting action often being indicative of an impending kick-back situation. 
         [0022]    The detection systems described herein may be used with a reaction system, such as those which either retract and/or stop the blade when certain conditions are detected. One such reaction system, which retracts the blade from the cutting zone when certain conditions are detected, is described in U.S. patent application Ser. No. 11/374,319, filed 13 Mar. 2006, which is hereby incorporated by reference. In addition to or in lieu of such a reaction system, the reaction system for the power cutting tool  10  may reduce the RPM of the motor spinning the blade when the certain conditions are detected. Additionally, the reaction system may sound an audible alarm when certain conditions are detected or provide a visual indication that the condition(s) has been detected. 
         [0023]      FIG. 1A  illustrates a power cutting tool  10  according to various embodiments of the present invention. In the illustrated embodiment, the power cutting tool  10  is a table saw comprising a table top or cutting surface  12 , a saw blade  14 , and a frame structure  16  above and spaced-apart from the cutting surface  12 . The frame structure  16  in the illustrated embodiment is part of a capacitive sensing system that also includes an electrically conductive strip  18  on the table top  12  in the shape of a rectangle that surrounds the blade  14 . The conductive strip  18  is preferably embedded in or bonded to the table top  12 , and is preferably formed with an electrically insulating top layer that may be formed or otherwise applied to a metal table top. The frame structure  16 , according to the illustrated embodiment, has a vertically oriented splitter  20  positioned behind the blade  14  that extends forwardly over a portion of the exposed blade  14 . The frame structure  16  may also include an electrically conductive upper frame  22  mounted to the splitter  20  that generally surrounds the blade  14  above the cutting surface  12 . In the illustrated embodiment, the upper frame  22  is rectangular and is preferably approximately the same size as the rectangular conductive strip  18  on the table top, but spaced away from the conductive strip  18  by a distance that varies in accordance with the height of the frame  16 , which may vary with the height of the blade  14 . This is because the splitter  20  is preferably connected to the frame structure of the blade assembly so that as the blade  14  is elevated or lowered, the splitter  20  maintains a relatively close spacing relationship with the blade  14  as shown in  FIG. 1A . Accordingly, the splitter  20  (and hence the upper frame  22 ) may move up and down with the blade  14 . Thus, the distance between the upper frame  22  and the rectangular conductive strip  18  can vary. 
         [0024]    The upper frame  22  and the lower conductive strip  18  are preferably in parallel with each other, and are preferably of the same geometric shape with identical (or nearly identical) dimensions. In the illustrated embodiment, the upper frame  22  and the lower conductive strip  18  are both rectangular, although in other embodiments different shapes and/or dimensions may be utilized. 
         [0025]    The lower strip  18  and upper frame  22  are electrically energized relative to each other with a sufficient voltage to produce a capacitive field that extends between them, which is diagrammatically illustrated by the curved lines  24  in  FIG. 1B . The capacitive field is monitored so that if an object is brought into the capacitive field, the capacitance that is being monitored will necessarily change, which may be used to trigger the reaction system if the changes are sufficient to indicate a condition worthy of triggering the reaction system. It is known that a person&#39;s hand can produce capacitance changes that are different in magnitude and phase compared to that which is produced by a work piece, such as a piece of wood. Procesing circuitry in a control system (not shown) can differentiate between these two conditions and appropriately trigger the reaction system when a person&#39;s hand is detected in the field. 
         [0026]    The use of the overhead frame configuration, such as illustrated in  FIGS. 1A and 1B , not only senses proximity to the blade  14 , but can prevent a slip condition where an object may be prevented from contacting the blade because it is physically blocked from doing so by the frame  22 . It is also possible to sense conditions that should trigger the reaction system at a higher elevation above the table top  12  than can generally be achieved with a capacitive sensing apparatus embedded in the table. The presence of the splitter  20  also reduces the risk of a kick back condition. 
         [0027]    A second embodiment of a power cutting tool  10  according to the present invention is shown in  FIGS. 2A and 2B . This embodiment is similar to the embodiment of  FIGS. 1A-1B , except that in the embodiment of  FIGS. 2A-2B  the upper frame  22  includes a number of optical emitters  34  and optical detectors  36 . The embodiment of  FIG. 2A-2B  also does not require the lower conductive strip  18  of  FIGS. 1A-1B . Instead, the embodiment of  FIG. 2A-2B  may comprise a detection zone  32  on the table top  12  oriented around the blade  14  and facing the upper frame  22 . In this embodiment, the emitters  34  emit optical energy downward toward the table top  12 , which is reflected by the detection zone  32 , with the reflected optical energy detected by the detectors  36  on the upper frame  22 . As such, the detection zone  32  may comprise a number of reflectors that are capable of reflecting the optical energy from the emitters  34  back toward the upper frame  22  (and hence the detectors  36 ). The number of emitters  34  and detectors  36  is preferably sufficient to provide a generally continuous zone of detection around the blade  14 . 
         [0028]    The presence or absence of an object may be detected by the interruption of the light path between the emitters  34  and detectors  36 . Further, the capability of differentiating wood from a portion of the operator may be obtained by differential reflectance, optical back-scattering effects, or by the operator wearing a glove having a specific signature. With such a light circuit detecting capability, it is apparent that the proximity of the object to the blade  14  can be detected and used to trigger the reaction system if necessary. 
         [0029]    The wavelength of the optical energy may be in the visible, infrared or ultraviolet portions of the spectrum, or some other wavelength. Also, according to various embodiments, each emitter  34  and detector  36  pair may be implemented in a single integrated circuit device and it may be sufficient to provide a number of them around the frame  22  spaced at, for example, one to two inch intervals, although larger or smaller intervals may be utilized, or the spacing intervals may vary depending upon the location. In other embodiments, the emitters  34  may be located in the upper frame  22  and the detectors  36  located in the detection zone  32  or vice versa. 
         [0030]    A third embodiment of the cutting tool  10  is shown in  FIGS. 3A and 3B . This embodiment is similar to the embodiment of  FIGS. 2A and 2B  except that in the embodiment of  FIGS. 3A-3B  multiple detection zones  32 A and  32 B are used. The detection zones  32 A and  32 B may be generally concentric to one another relative to the blade  14 . The inner zone  32 A may be configured to operate with a first emitter/detector combination  34 ′- 36 ′, whereas the second zone  32 B may operate with a second emitter/detector combination  34 ″- 36 ″. It should be understood that if the detection zones  32 A and  32 B are reflecting surfaces (e.g. if the detection zones  32 A,  32 B comprise reflectors to reflect optical energy back toward the frame  22 ), they are preferably angularly oriented in the table top  12  to reflect the light back to the appropriate detector. Also, it should be apparent that if the detectors do not operate on the principal of reflection and are mounted in the table top  12 , the emitters  34 ′,  34 ″ may have a sufficiently narrow emitted beam so that a detector located in the detection zone  32 B will not detect emitted light from emitters that are directed to the zone  32 A and vice versa. Alternatively, there can be an emitter in the frame  22  that provides a broad beam of light to detectors in both zones  32 A and  32 B, and detectors in each of the zones  32 A,  32 B could independently detect the absence of emitted light, which may indicate that something is in one or both zones  32 A and  32 B. 
         [0031]    Assuming that the emitter/detector combinations are operable to detect the presence of an object, the embodiment of  FIGS. 3A-3B  enables the approach velocity of the object to be detected by calculating the time difference between the outer zone  32 B and inner zone  32 A. This can be used to provide different reactions for penetration into different zones. In this regard, the reaction system can issue an audio warning before it triggers stoppage or retraction of the blade in response to penetration of different zones. 
         [0032]    A fourth embodiment of the power cutting tool  10  is shown in  FIGS. 4A and 4B . In this embodiment, the frame  22  includes, for example, a relatively small end portion  56  at the forward end of the splitter  20 . A number of optical energy emitters (not shown) may be located in the end portion. In this embodiment, it is preferable that the detection zones  32 A and  32 B have optical energy detectors (not shown) located in the table top  12 , although it is possible to have a number of mirrors located along the zones  32 A- 32 B configured to reflect energy back toward detectors located in the end portion  56 . However, because the blade  14  can still typically be raised or lowered in most table saws, if there are mirrors embedded in the table top  12  in the zones  32 A and  32 B, the angle of reflection would necessarily change as the blade elevation is changed. 
         [0033]    In this embodiment, there preferable is a sufficient number of emitters to direct light toward all of the detectors and any one of the detectors could provide a detector signal indicating the presence of an object during operation in the sensing zone around the blade  14 . Having the detectors in the end portion  56 , while possible, provides a greater engineering challenge than locating the emitters in the detection zones  32 A and  32 B. 
         [0034]    A fifth embodiment of the cutting tool  10  is shown in  FIG. 5 . In this embodiment, a single optical emitter/detector pair  37  is connected to the splitter  20  above the table. An optical energy beam is directed downwardly from the emitter onto the work piece  62  and the height of the work piece  62  above the table  12  can be effectively measured based on the return signal detected by the detector. As the work piece  62  is moved into the blade  14 , any substantial detected increase in the height can be interpreted as an undesired object on top of the work piece  62  that can be used to trigger the reaction system. 
         [0035]    A sixth embodiment of the cutting tool  10  is shown in  FIGS. 6A and 6B . This embodiment does not have an overhead sensing structure like the previous embodiments. In this embodiment, an optical distance sensor  60 , such as, for example, an optical mouse, is embedded in the table  12  at a location near the rear reach of the blade  18 , with the optical distance sensor  60  positioned to monitor a work piece  62  as it is being cut. If the optical distance sensor  60  detects that the work piece  62  is rising from the surface  12 , this is an indication that a kick-back situation may be occurring. The detection of the work piece rising preferably triggers the actuation of the reaction system. It should be understood that the embodiment of  FIGS. 6A and 6B  does not include a splitter. In this regard, it should be understood that the embodiment of  FIG. 6  could be used in combination with one of the overhead detecting embodiments shown in  FIGS. 1-5  or it could be used separately and independently from the other embodiments. 
         [0036]    While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims.