PRODUCTIVITY ENHANCEMENT FOR BAND SAW

Abstract

Machine vision apparatus tracks a distinctive object in relation to a hazardous location on a work surface of a modified band saw in two, three, or four (3-D+T) dimensions, and calculates whether to send an “immediate shut-down signal” to the band saw. Cameras and an image processor are mounted on the band saw. The signal causes an integrated blade-arresting or stopping mechanism to immediately shift the idler wheel, removing blade tension and disconnecting the blade which is then braked to a complete, safe stop before an approaching blue-gloved hand can touch the blade.

Claims

1-16. (canceled)

17. A powered machine of a type wherein a human operator uses his or her hands to present material to a movable means for cutting or shaping the material; the means being located within a three-dimensional hazardous zone having a height, a width, and a depth and in a position in relation to a frame of the machine; wherein the machine is provided with integrated safety protection apparatus including (a) three-dimensional optical risk determining means responsive to an instantaneous position in three dimensions of the operator's hands, as compared to the known position of the hazardous zone, and (b) actuator means for immediately stopping motion of the cutting or shaping means in response to an output of said risk determining means indicating that the operator's hands are at risk of entering the hazardous zone, thereby rendering the machine safe.

18. The powered machine of claim 17, comprising a bandsaw (100); the movable cutting or shaping means comprises an exposed portion of an inextensible saw blade in the form of a band having cutting teeth along an edge and operatively disposed to pass over a first or driving wheel (114) driven by a motor (115), and over a second or idler wheel (113) while the blade is maintained under a tension during use thereby causing the blade to be coupled to both wheels by friction, wherein the three-dimensional optical risk determining means comprises: (a) illumination means (303, 304) directed to a volume viewed by a set of at least two spaced-apart imaging devices (118a, 118b) mounted upon a frame of the bandsaw; said field of view including a surrounding zone (406) containing the entire hazardous zone (405); image processing means operatively connected to receive images communicated from each said imaging device; said image processing means being programmed to supervise, when in use, the surrounding zone, to locate the position of the operator's hand or hands (401, 402) in each image and compare the at least two images in order to derive an instantaneous position in three dimensions of the operator's hand or hands within a surrounding supervised zone for which purpose the operator's hands are rendered identifiable by being enclosed, when in use, in flexible blue gloves; said image processing means being further programmed to calculate, when in use, a proximity of the operator's hand or hands with respect to the hazardous zone (405) in three dimensions and on establishing a state of risk, to send a SIGNAL along a communicating channel to the actuator means; (b) the actuator means includes means adapted to receive the SIGNAL from the communicating channel and at least one actuator capable, when in use, of halting motion of the saw blade before the worker's hand or hands enter the hazardous zone at any height.

19. The powered machine as claimed in claim 18, further wherein the three-dimensional optical risk determining means calculates the position of the operator's hand or hands over time from a series of images and is programmed to send the SIGNAL in an event of anticipating an approach of the operator's hand or hands to the hazardous zone, thereby causing the driven saw blade to cease motion before the worker's hand or hands enter any part of the hazardous zone.

20. The powered machine as claimed in claim 18, further wherein the three-dimensional optical risk determining means calculates a speed of the operator's hand or hands over time from a series of images beyond the surrounding zone, and is programmed to send the SIGNAL in an event of detecting a speed of over 3 metres per second thereby causing the driven saw blade to cease motion before the worker's hand or hands enter any part of the hazardous zone.

21. The powered machine as claimed in claim 18, wherein the actuator means includes a first actuator capable, when in use, of maintaining an axle supporting the second or idler wheel (113) in a first position that holds the blade under a working tension until the actuator means receives the SIGNAL, whereupon the first actuator causes the axle to move to a second position closer to an axle of the first or driving wheel, thereby removing tension from the saw blade and decoupling the blade from both wheels.

22. The powered machine as claimed in claim 20 wherein the axle supporting the idler wheel is maintained in position by an over-centre latch (604, 606, 607) held in place against a force imposed by tension within the saw blade by the first actuator (511).

23. The powered machine as claimed in claim 21 wherein the axle supporting the second or idler wheel is capable of being reset under a manually initiated self-resetting procedure thereby restoring tension in the saw blade.

24. The powered machine as claimed in claim 20 further wherein the inextensible saw blade (101) is operatively disposed to pass through a brake assembly including a brake shoe, wherein a second actuator (706) operatively connected to the brake assembly (700, 701, 702) releases the brake assembly when activated thereby allowing the saw blade to pass, and when the second part of the safety protection apparatus receives the SIGNAL, the second actuator is deactivated, causing the brake assembly to close around and grip the blade, thereby stopping the saw blade by friction against the brake shoe (701).

25. The powered machine as claimed in claim 18 wherein the optical risk determining means is capable of initiating transmission of the SIGNAL within a time of 30 milliseconds after detection of a gloved hand approaching any part of the hazardous zone.

26. The powered machine as claimed in claim 23 wherein the actuator means is capable of capable of bringing the saw blade to a halt within a time of 40 milliseconds after receiving the SIGNAL.

27. The powered machine as claimed in claim 24, wherein the machine includes self-monitoring means for ensuring a safe maximum braking time is not exceeded; the self-monitoring means comprising a process of bringing the band saw blade up to an operating speed while monitoring saw movement speed, then generating the SIGNAL to cause the blade to stop, and verifying that the blade has stopped within a predetermined time limit.

28. The powered machine as claimed in claim 19, wherein the actuator means includes a first actuator capable, when in use, of maintaining an axle supporting the second or idler wheel (113) in a first position that holds the blade under a working tension until the actuator means receives the SIGNAL, whereupon the first actuator causes the axle to move to a second position closer to an axle of the first or driving wheel, thereby removing tension from the saw blade and decoupling the blade from both wheels.

29. The powered machine as claimed in claim 20, wherein the actuator means includes a first actuator capable, when in use, of maintaining an axle supporting the second or idler wheel (113) in a first position that holds the blade under a working tension until the actuator means receives the SIGNAL, whereupon the first actuator causes the axle to move to a second position closer to an axle of the first or driving wheel, thereby removing tension from the saw blade and decoupling the blade from both wheels.

30. The powered machine as claimed in claim 25, wherein the machine includes self-monitoring means for ensuring a safe maximum braking time is not exceeded; the self-monitoring means comprising a process of bringing the band saw blade up to an operating speed while monitoring saw movement speed, then generating the SIGNAL to cause the blade to stop, and verifying that the blade has stopped within a predetermined time limit.

Description

DRAWINGS

[0045] FIG. 1: is a diagram of a band saw with an idler wheel dropping mechanism.

[0046] FIG. 2: shows a modified band saw according to the invention, including safety means for the operator.

[0047] FIG. 3: is an oblique view of the lights and cameras for a 3D version of the invention.

[0048] FIG. 4: is a schematic of the protected areas upon the work surface 102.

[0049] FIG. 5 is an oblique view of a second idler wheel dropping mechanism.

[0050] FIG. 6: is an end elevation view of the second idler wheel dropping mechanism.

[0051] FIG. 7: is an elevation view of a caliper brake to stop the decoupled blade.

[0052] FIG. 8: is a block diagram of steps in example software.

[0053] FIGS. 9 as 9a, 9b and 9c are drawings from a video record, showing a response.

INTRODUCTION

[0054] A “video curtain” type of guard to protect a person against injury when using a modified hazardous machine is described. Machine vision apparatus uses overhead cameras to track the instantaneous location of a visually distinctive object over a machine work surface in at least two dimensions (X-Y) and assesses the risk of danger to that object in relation to a hazard at a fixed position on the surface. The visually distinctive object is declared in this Embodiment to be an operator's hand inside a blue glove. One improvement adds 3D (X-Y-Z) vision so that a protected volume is created. Another improvement tracks the movement of the object over time (X-Y-Z-T) and can anticipate if or when an object already detected but far from the hazard might inadvertently reach the hazard if it continues in its present path.

[0055] The machine vision means generates an “immediate shut-down signal” command (herein referred to as “SIGNAL”) and sends it to process control means within the hazardous machine. Action avoids injury and damage. This specification primarily refers to a band saw on which dismembered carcasses or parts are cut up by an exposed blade moving at a speed of typically 1400 feet per minute, as used industrially for butchering or rendering purposes in a meat or poultry plant. A skilled addressee will be aware that the concepts disclosed here can be applied to a variety of other hazardous machines such as in sawmills and presses, even noodle rollers.

[0056] FIG. 1 and a related description (see later) shows a first version of a band saw modified by provision of blade detensioning means, on reception of a SIGNAL. FIGS. 5, 6 and 7 and associated text describe a second version in more detail.

[0057] FIG. 2 shows a band saw incorporating a version of the invention, in which an operator (208) is standing in front of a work table (102) that has a conventional slot through which a toothed blade or band (101) passes. (118) indicates attached cameras and lights in general. (203) houses the idler wheel, now having a modified axle support. Items under the work table (115)—a motor, and (206)—a housing for a drive wheel, are conventional. The drive wheel itself is not shifted during action of this embodiment. This band saw is provided with a housing 204 to conceal the idler wheel dropping means (see later) and a housing (205) concealing the blade halting control equipment. Housing 204 also conceals blade tension resetting means (see FIGS. 5 and 6) so that work can be continued after resetting is done. Note that the same principle cam be applied to a band saw in which the motor is above the work surface and the idler wheel is below.

[0058] FIG. 3 shows a preferred location for two colour or blue-sensitive cameras (118a, 118b) (here called “L” and “R”) to collect the images to be analysed. These examples operate at a 6 millisecond (mS) frame rate and are mounted about 1 metre above the work surface. Each one is at a slight angle to either side of the blade 102 so that none of the work surface is hidden from both cameras. The lenses and cameras are selected to cover an area on the work table (102) of about 400 mm×400 mm. For good depth of field the camera lenses are stopped down so that a sufficiently sharp image has at least a 400 mm depth. For low noise with these cameras when the lenses are stopped down a white light of at least 1500 lumens on the surface is provided by LED lamps (303, 304) to each side of the cameras.

[0059] According to the invention, proximity detection for the operators' hands relies on the operator wearing gloves (401, 402) that are coloured blue, which is already a normal practice in the meat and poultry industry. Blue enhances contrast. Blue stands out from the red of muscle, the creamy white of bone, or the white of tendon and ligament. Therefore this specification will use “blue” as a term to describe a distinctive hue for use in at least the meat industry. Then the proximity detection problem becomes one of detecting the positions of blue objects in a field of view. The skilled addressee will be able to relate the following 3D description to a 2D, single camera version.

[0060] With reference to FIG. 4 showing an operator's view of the working area, the hazardous zone is defined as the zone occupied by the band saw blade (101). A virtual surrounding zone (405) within which detection of a blue glove causes the machine to stop is comprised of an arbitrarily determined safe distance of perhaps 50 mm from the blade to left, to right, toward the operator, and away from the operator. The machine vision equipment is intended to supervise the positions of blue objects (such as gloved hands 401 and 402) in a virtual supervised zone (406) extending over most or all of the entire work surface (102), and take action if any recognised object appears to be in a dangerous state; such as if the object is moving quickly.

[0061] As will be described below, frames of data take 20-30 milliseconds (mS) to be processed through a series of steps to make a SIGNAL or not, using a computer processor located in an equipment compartment attached to the band saw head. Physical halt of the blade should take up to 24 mS after receipt of the SIGNAL. The apparatus is designed to test the braking speed from time to time, employing a beam of light transmitted past the blade teeth where it is interrupted or modulated by the passing teeth as a transducer of blade motion. If the time to brake exceeds 40 mS the machine enters a disabled state and maintenance is requested. It will remain disabled until serviced. Both steps—connecting and braking—are initiated at the same time in the present embodiment since inherent physical delays provide that the brake does not try to work against the idler and drive wheels while stopping the blade.

[0062] Cameras (118a) and (118b) are mounted on the band saw frame as per FIGS. 2 and 3. The cameras' outputs are digitized and, as shown in block diagram FIG. 8, are separately processed in blocks (801) and (802) in order to discriminate “a relative amount of blueness only” in each pixel—while rejecting intensity variations as might arise within a shaded area. Such a simplified frame representing colour alone, independent of brightness, is convenient for subsequent processing. Suitable selection of working conditions; glove colour and lighting minimized a need for frame “cleaning” of any kind such as for noise cancellation. A recognised “object” to be tracked should comprise a contiguous array of blue pixels corresponding to both gloved hands if in the frame, or may represent each finger of the gloved hand. It may be suitable to use a central member of an edge of an X-Y array of nearest-to-hazard detected pixels—which would look like an arc facing the blade (101) if seen on a screen, to represent each object. (A line-based recognition technique, seeking speed, is described below).

[0063] Each pair of L and R frames are combined, and X and Y positions of corresponding shapes in each frame are compared. On taking viewing point separation into account this part of the image processor (803) computes a relative height or Z position for each shape. The objects are now located inside a three-dimensional (3-D) volume, meaning that the height of the exposed blade (101) in FIG. 2 is surrounded by a 3-D surrounding zone; entry into which by a recognized object causes the band saw to halt. 3-D processing techniques derived from left and right image comparisons are well-known to the reader skilled in the art.

[0064] Stored constants defining the actual hazard zone as a volume are compared with the located identifiable shapes in block (805), in order to determine the distance of the closest point of any one “blue object” or blue glove (401,402) to the hazard. In this description, the hazardous zone is defined as the zone occupied by the cutting teeth of the band saw blade (101). The invention protects gloved fingers from likely contact with the cutting teeth by stopping the blade immediately if an identified object (gloved finger or hand (401 or 402)) enters a cubic shape, the surrounding zone that is also as high in the Z axis from the table surface as is the height of the hazardous zone—the exposed blade. A cubic surrounding shape aligned along Z and Y axes is easier and quicker to process than a rounded or angled shape, although any shape could be represented in a lookup table. The surrounding zone is surrounded by a supervised zone.

[0065] It will be appreciated that meat to be sawn (403) has a relatively low proportion of visible blue content as seen by the cameras. (White areas, also having high blue, are matched by high red and high green content pixels). Therefore approach of meat alone to the blade (101) across the surrounding zone is not noticed and does not cause the band saw braking process to be activated.

[0066] According to this approach detection of an object having sufficient contiguous blue pixels that is located within the surrounding zone will immediately send the SIGNAL along channel 807, probably a wire, to operate two actuators (511 and 706) via conventional process control equipment. Computer “intelligence” allows the equipment to anticipate a problem and take action in advance in case a quickly moving hand hits the blade (101) before the blade can be brought to rest in a suitably controlled way. Perhaps a quick movement is unlikely. But accidents tend to happen in unpredictable ways. The invention is unlikely to protect an operator who does not use a distinctive glove—assumed herein to be blue.

[0067] One method for adding a time element is to maintain an (X-Y-Z-T) table of an appropriate number of the most recent X-Y-Z positions over time for each of n separately recognized objects. Each new record would displace the oldest record for each object. After adding each new record, the processor calculates a three dimensional vector to assess where the recognized object will be at a selected moment in the future, taking into account how long the band saw blade takes to be stopped. For example, if the vector, extrapolated forward beyond the present time by an example maximum braking time of 30 mS will transgress the hazardous zone or the surrounding zone, the SIGNAL is made, immediately bringing the blade to a halt.

[0068] Another method is to declare that any blue object detected outside the surrounding zone as moving at a predetermined dangerous speed of more than for example 3 metres per second will cause a SIGNAL to be made.

[0069] At this time one preferred method for speeding up processing is to dissect the X-Y planes from the cameras inside block 803 into a series of perhaps 16 separated virtual horizontal lines, as if the cameras were line scanners. Then the virtual analysis point simply travels along all lines, determining if the pixel at the point is blue or not, and stops travelling and reports a position in X, Y when the pixel is not blue. The actual positions of the lines in the Y axis is changed from frame to frame so that over a short period of time the entire frame is covered and the objects become defined by their edges. This dissection might not be required if faster processors were used.

[0070] Perhaps one image or pair can be taken in before the previous image, received 6 mS earlier, has been completely processed. A number of separate image analysis procedures may be maintained in parallel, like a round or perpetual canon in music; each frame (or pair of frames) being processed at one stage while other frames are at different stages. A processor with 4 cores, for example, could handle one analysis process image in each core, combining the SIGNAL outputs, and possible control-panel commands with an OR function.

[0071] In the Example, software is written in a high-level language such as C++ and care is taken to ensure that the operating system (which may be Windows®) is not able to interrupt this time-critical image analysis for non-relevant purposes. For example, interrupt priority settings that the operating system might use are set at a lower priority than this image analysis process. Safety requirements dictate that this apparatus is made “fail-safe” throughout—that is, if anything goes wrong, the blade is halted immediately. For example at the brake itself, power is continuously applied to solenoid (706) during normal use to pull a spring-loaded armature into the device and keep the brake off. If there is an interruption to power, the brake is applied. The image analysis software is written with checks in order to ensure that it will default to a safe basis in event of, for example, software or hardware failure. One way to maintain safe software is to include at least one independent “watchdog timer” perhaps in separately powered electronic hardware apart from the computer electronics itself, which will count up to a preset maximum and issue an immediate-halt SIGNAL if it is not reset to zero frequently by the software such as each time the program completes a software loop. Other means include maintaining and testing checksums, as will be known to a person skilled in the software arts.

[0072] The blade decoupling mechanism, controlled by the SIGNAL, will now be described.

[0073] FIG. 5 is an oblique view, and FIG. 6 is an end elevation view of the resettable mechanism to decouple the band saw blade (101) about an idler wheel in event of a dangerous situation. A skilled reader will realise that a band saw in which the motor and drive wheel are above the work surface and the idler wheel is located below can be modified according to the same principles in order to install a blade decoupling mechanism, since blade tension is a dominant force.

[0074] The blade (101—not shown here) passes around the idler wheel (113) and in normal use is maintained in substantial tension by the shaft (103) of the wheel, mounted on bearings inside block (502), being placed in a “tension position”. Block (502) can slide vertically along a pair of fixed rods (503, 504) anchored at each end in a fixed block (505, 506) and provided with end adjusting bolts such as 609. Block (502) is pressed up by pressure from compression springs 385 (507) around the rods, the springs being supported on a releasable, sliding block (508) which has been pushed up along the two rods by pneumatic actuators (509, 510), during a “Set and Recouple” process. The travel is controlled by a limit switch (not shown). On reaching a working position the catchblock (502) is locked in place by a tooth (604).

[0075] The analogue to the over-centre actuator of the early version as illustrated in FIG. 1 is a release mechanism for the catch block (601) and tooth (604) at one end and a pivot mount (602) at the other end; with pressure applied through spring 603). The SIGNAL from the machine vision unit or from an operator emergency stop button (not shown) causes actuator or solenoid (511) to push rod (605) down, so that beam (606) which is supported by pivot (607) at one end is pushed down and the support wheel (608) at the other end is pushed over centre, removing support from the tooth (604) on block (601). Tension in the band of the band saw gives rise to a release force applied to tooth (604) along a vector that is down and to the right. The now unsupported tooth (604) releases the block (508). The idler wheel (113) on its shaft (103) supported by block (502) rapidly falls over a short distance, sufficient to take tension off the saw band (101—not shown in FIG. 5 or 6) and decouple the saw band from the rim of the idler wheel (113) so that braking can immediately take place (see in relation to FIG. 7). The rate of idler wheel acceleration is significantly greater than the force of gravity (g) because of the tension in the band and because of released compression in springs (506, 507), in combination with the mass of the idler wheel alone.

[0076] A skilled addressee will appreciate that other permutations of the apparatus such as to hold and then release the idler wheel may be created. This mechanism is compact and is quick to operate.

[0077] FIG. 7 illustrates an effective blade braking mechanism used in company with the decoupling mechanism to bring the blade (101 which is shown diagrammatically in part of this drawing as a dashed line) to a halt. The mechanism is securely mounted toward the rear of the band saw housing and acts upon the blade (101) as it rises up toward the idler wheel after turning around the drive wheel. A caliper brake uses a securely fixed metal block (700) mounted on a rigid base as one shoe. A pivotally mounted brake shoe (701) of metal can press the sides of the blade, but not the teeth, against block (700) thereby causing substantial friction without imposing any significant curvature on the blade, and without touching the teeth. It has been estimated that about 200 J of power is taken from the moving blade and dissipated as heat within the block over 24-30 milliseconds (mS) and over about 10 mm of blade length during a braking action. There would be much more power to transfer, and a much longer braking process, if the idler wheel, drive wheel and motor also had to be slowed to a stop through the saw blade with this brake. There may be residual friction between the blade and the still spinning driver and idler wheels. Those parts may be stopped more quickly such as by application of other brakes (not shown) and by disconnecting the motor (115) from a supply of electricity or applying reverse power to the motor.

[0078] A powerful solenoid (706) is normally ON during use and holds the brake in a released state. When de-energised by the SIGNAL, rod 705 is pushed up against block 702 by spring pressure (spring 710). That block is pivotally mounted by pivot (703) so that second pivot (704) which holds the brake shoe moves up and in an arc toward the position of blade (101), forcing the brake shoe into frictional contact with the blade. Usually the solenoid remains de-energised for sufficient time to ensure that all motion has stopped and the blade will not start to move if the brake is released too soon. The dissipated power may cause the brake to stick in place, depending on any coating over the blade. Brass is a currently preferred brake shoe material, since steel tends to form welds. In this version a pneumatic release actuator (709) is placed above the brake assembly in order to extend a rod (708) toward the brake shoe mount (704) under process control when the actuator is operated during a “reset” procedure and force the brake to open. Motion of the rod (708) can be monitored by a limit switch (not shown) so the control apparatus can sense whether or not the brake has actually been released.

[0079] Turnbuckle 610 and arm 611 are part of an idler wheel angle trimming assembly used to ensure that the blade runs true.

[0080] An alternative version of the idler wheel dropping mechanism is now described.

[0081] Reverting to FIG. 1, a modified band saw (100) of the type used in the meat industry and in boning-out rooms, comprises a horizontal working surface (102) through which is passed a vertically directed cutting edge produced by passage in a first direction (down) of a metal tooth-bearing band (101). The band is a closed loop passing around a large motor-driven driving wheel (114), returns along a path remote from the working surface and closes a loop around a large idler wheel (113), above the working surface. Usually the driven wheel and motor (115) are under the working surface and the idler wheel is above. As always, the driving and idler wheels have parallel axes of rotation and are mounted at an inter-axis spacing that provides, during normal use, that the metal band (101) is maintained in elastic tension while not extended into a region of ductile flow.

[0082] FIG. 1 includes an example mechanism including an “over-centre” mount made of sets of two articulated levers as (107) and (108), inside a housing shown by dashed lines. The over-centre mount is tripped by an electrical signal energising the solenoid actuator (111), to pull shaft (109) to the right, and as a result to physically move idler wheel (113) by its shaft (103) downward and closer to the drive wheel (114). This motion includes an “over-centre” mechanism implicit in the knuckled joints between beams (107, 108) and the second pair, that support bearings (104, 105) of the shaft (103). As a result of moving idler wheel (113) downward and closer to the drive wheel (114), tension in the blade that gave rise to static friction that coupled the saw blade (101) to the driver wheel (114) and the idler wheel (113) is removed and the blade can be stopped by a braking means (not shown) without having to stop the spinning wheels (113, 114) and motor armature (inside 115).

[0083] If a solenoid (111) is employed, it may be energised for example by passing a half-cycle of mains power through the winding using a thyristor as a control means, thereby pulling shaft (109) to the right, past the over-centre point of balance. A preferred solenoid is designed for a powerful impulse, such as to not reach magnetic saturation when driven in that way. The weight of the wheel (113) plus the tension in the blade (101) assists the downward progress of shaft (103) and may accelerate its motion beyond that provided by gravity alone.

[0084] There may be residual friction between the blade and the still spinning driver and idler wheels. Those parts may take some seconds to come to a halt, and may be stopped more quickly such as by application of brakes and by disconnecting the motor (115) from a supply of electricity or reversing it if it is suitable for such operation.

[0085] In this version, the band saw can be reset after an incident is over and after the motor and idler have certainly stopped (when current though solenoid (111) has ceased), is to manually push the handle (112) to the left as referred to FIG. 1, so that the shaft (103) resumes its higher, over-centre alignment parallel to the axis of rotation and the cutting blade is again stretched into frictional contact with the two wheels.

[0086] Inclusion of process control means allows a systematic check list to be used at each station and for each shift or change of operator, in order to raise the level of safety provided. For example the blade can be brought up to speed and the duration of a stopping procedure can be checked by machine, to ensure that the band saw is safe. A display screen driven by the computer may be made to show the state of the check list and what must next be done, although during normal operation the screen may simply show a brand name or be blank. The list can include “show me your blue gloves” for example, just in case an operator intends to work bare-handed.

[0087] A check list could be wired into an interlock that prevents the motor from starting until for example it has proven that it is in fact capable of detecting and responding to presence of a blue area inside any designated zone. The blade would not be activated at this time. But if a new operator wanted to become confident with the band saw, the moving blade and the braking system can be operated in a test situation without harm.

[0088] Details of an “action plan” for responding to every signal that warns of a transgression of a hazardous zone or any proportional response to other movements (without actually generating a SIGNAL) may require human elements including worker's union requirements to be considered. The device is capable of reporting every movement to a monitoring device so that a manager is made aware of a tired operator's rising rate of transgressions of the safe zones.

Variations

[0089] Blue has been specified as a desirable glove colour for this machine vision process because blue gloves are already in wide use as a safety measure for visual purposes; because blue matches a channel of an RGB camera, and because a predominantly blue light is distinct for machine vision purposes from red, yellow, and white light as returned from meat products under white light. A fluorescent “dayglow yellow” glove is one of many possible alternatives.

[0090] The ubiquitous band saw has been described here. A “motor on top” version is a simple conversion of the FIGS. 2-8 embodiment. Other powered cutting tools used in the meat industry, including circular saws, are susceptible of like improvement.

[0091] By use of “graded proximity”, whether incremental or not, the incident detector may be arranged to respond in a graded manner to a severity of any incident, by making use of computational procedures. As the operator's body or hand gets closer to the moving knife, severity is graded as more intense.

Results

[0092] See FIGS. 9a, 9b and 9c, drawn from stills, which show three consecutive frames showing the reaction of the apparatus as described in FIGS. 2-8 to a fast-approaching blue-gloved hand. These were was filmed with an Iphone 5®, assumed to have a frame rate of 33 mS per frame. A test blade bearing painted cross-stripes and no teeth was operated. The frame in FIG. 9a does not show any visible braking response in the machine and no markings on the blade can be seen. The hand was 4-5-5 cm from the blade. The original of the next frame used for FIG. 9b showed that braking had started because the rear section of the band had become deviated sideways, but again, and no markings on the blade can be seen. The original of the last frame in FIG. 9c showed the cross stripes drawn on to the blade as partially sharp and partially blurred; the blade had halted during the exposure.

Advantages

[0093] Part 1: Detection means. Advantages of this invention over the prior art include: [0094] (1) It is a “video curtain” kind of protection requiring no changes be made to the way that the hazardous equipment is used and no physical obstructions are added. [0095] (2) The object to be optically sensed is already widely used—namely a flexible (rubber or latex) blue glove. Unlike prior-art use of conductive gloves for which actual contact is a pre-requirement for a braking operation and for which a connecting wire might fail, a blue glove is a fail-safe option. “Check-list” functions may be included in software. [0096] (3) Hand injuries are avoided by anticipating contact; either by simply detecting that a gloved hand is within a dangerous zone as assessed in an X-Y plane; better by use of a three-dimensional protected area using 3-D processing and a pair of cameras to derive position in an X-Y-Z volume, and in addition by evaluating movement of the detected object across the image into a course taken in the future (X-Y-Z-T), so that even a quick accidental movement of the gloved hand is properly assessed and protection is applied if a risk of injury is determined. [0097] (4) Stopping the blade using the apparatus carries no penalty because the blade is not damaged as a result of the sudden stop. [0098] (5) The operator benefits from working under the copious white light used to illuminate the scene. [0099] (6) Computer processing is inherently capable of anticipating and grading any incident particularly to determine if an immediate-halt signal must be made. Signs of a tired or otherwise dangerous operator as actual blade stoppages or near misses; one by one or as a summary can be related to a manager through an intranet. Fatigue, illness, or the like can make a particular person unusually susceptible to injury on particular days. [0100] (7) The present invention reduces injury, reduces insurance costs, and reduces down time as a result of inadvertently caused injury to skilled operators. [0101] (8) Band saws in educational establishments teaching wood work to children would benefit from this safety apparatus.

[0102] Part 2: Braking means. Advantages of this invention over the prior art include: [0103] (9) that the blade of the bandsaw is disengaged from rotating parts of the band saw (including idler wheel, drive wheel, shaft and motor armature) thereby reducing the mass that has to be brought to a rapid stop. That allows a faster halt, even while the wheels are still spinning, with lower requirements imposed on brakes. In particular the integrity of the blade itself is not affected. Blade replacement is not required. If the blade was to break, flying parts may cause injury or damage or contaminate the food materials being dismembered. [0104] (10) that the mechanically resettable mechanism is not complex and, being comprised of mechanical parts and solenoids, is compatible with the capabilities of most service organizations. [0105] (11) That the invention allows a cutting machine to be used by an experienced operator without impediment as would be caused if a physical guard was placed around the band saw blade or gloves connected to wires had to be used.

[0106] Finally it will be understood that the scope of this invention as described and/or illustrated herein is not limited to the specified embodiments. Those of skill will appreciate that various modifications, additions, known equivalents, and substitutions are possible without departing from the scope and spirit of the invention as set forth in the accompanying claims.