Panel saw with safety device to avoid injury during cutting

Abstract

The present invention relates to a circular saw, in particular a panel saw, comprising a support surface for a workpiece having a saw blade slot, a main drive motor arranged below the support surface for bringing the saw blade into a rotational movement, a saw blade holder connected to the main drive motor for transmitting the rotational movement and comprising a saw blade bearing unit and a saw blade flange mounted by the saw blade bearing unit for rotation about the saw blade axis and designed to be connected to the saw blade in a fixed manner under tension, a height adjustment device comprising a height actuator and a transmission element connected to the saw blade holder, arranged and designed to set the spacing between the saw blade holder and the support surface, and an electronic interface for inputting the protruding height of the saw blade.

Description

[Technical Field]

[0001] The present invention relates to a circular saw including a support surface for supporting a workpiece and having a saw blade slot, a main drive motor arranged below the support surface for rotating the saw blade, a saw blade holder connected to the main drive motor for transmitting the rotational movement and comprising a saw blade bearing unit and a saw blade flange mounted by the saw blade bearing unit for rotation about the saw blade axis and designed to be connected to the saw blade so as to be fixed in torsion, a height adjustment device comprising a height actuator and a transmission element connected to the saw blade holder and arranged and designed to set the spacing between the saw blade holder and the support surface, an electronic interface for inputting the projection height of the saw blade, a control device connected by signals to the electronic interface and the height actuator and designed to operate the height actuator so that the projection of the saw blade input via the user interface is set by the height actuator, and a protection device having a monitoring device for recording dangerous situations and for quickly lowering the saw blade in dangerous situations.

[0002] A circular saw is a machine tool used to make straight cuts in boards, sections, bars, and planks. Circular saws can be configured as relatively small DIY saws for occasional use by amateurs, as handy circular saws for mobile use on construction sites, or as panel saws for use in carpentry shops and similar professional applications.

[0003] A panel saw is a specialized machine tool used in carpentry shops and other industrial or artisanal workshops to cut wood, materials with similar physical properties, plastics, minerals, and light metals to size. A panel saw generally features a support surface that supports the workpiece and a saw blade that projects from the support surface through a slot and rotates around a saw blade axial shaft located below the support surface to make the sawing cut. To make the sawing cut, the workpiece can be pushed relative to the saw blade axial shaft. For this reason, in a typical panel saw used in an artisanal workshop, the workpiece can be moved against the support surface, particularly the slide portion of the support surface, with a small force, while the saw blade axial shaft remains stationary while the sawing cut is made. Unlike a table saw, where the operator operates from the front and can grip and push the workpiece on both sides of the saw blade, the operator stands to the side of the saw blade. [Background technology]

[0004] An alternative embodiment of the panel saw is one in which the workpiece is fixed so as to be stationary on a support surface and the saw blade is arranged on a translatable saw blade unit to perform the sawing cuts, in which case the saw blade is set to move in a translational manner to perform the sawing cuts. Panel saws are generally already known from EP2 527 069 A1, DE20 2009 007 150 U1 or WO2012 / 159956 A1.

[0005] Panel saws are characterized by high cutting quality and precision, and are capable of sawing at high capacities. This allows them to cut through solid wood and very thick workpieces. For this purpose, panel saws can be fitted with saw blades of different diameters, ranging from 10-15 cm to very large circular saw blades, for example with a diameter of 55 cm.

[0006] Despite the traditional safety devices, such as a guard that covers the saw blade from above and also serves to eject sawdust, and a push rod that can push small workpieces close to the saw blade, and despite the fact that panel saws are often used by skilled operators who have received special training in using the machine, accidents involving operators being cut on the panel saw blade are frequent. Such injuries usually take the form of amputation of a part of a finger, a finger, or a hand.

[0007] The inventors have discovered that these injuries can be caused by a variety of incorrect or accidental work procedures. A common cause is inadvertently removing cuttings from around the saw blade while moving the hand quickly around the blade, resulting in contact with the blade and injury. Other causes include the hand slipping off the workpiece while pushing it forward, or careless user actions such as tripping, working under time pressure, or poor coordination when multiple operators are working on the panel saw.

[0008] To prevent such injuries, active safety devices have been proposed in place of traditional passive safety devices. The American manufacturer SawStop®'s system, based on the difference in the conductive and capacitive behavior of wood and body parts at the saw blade, uses contact between the saw blade and a body part as a trigger to distinguish it from contact between the saw blade and a workpiece. Its purpose is to stop the saw blade as quickly as possible, thereby preventing serious injury. This system has been shown to be able to prevent serious injuries in certain use situations. However, a drawback of this system is that sudden braking generally involves irreparable damage to the saw blade, and the detection system makes it impossible to prevent serious injury in certain accidents, especially when a body part approaches the saw blade quickly. This protective system is described, for example, in EP1 234 285 B1, WO2017 / 210091 A1, and US2014 / 0331833 A1.

[0009] The inventors have discovered that attempting to prevent injury solely through saw blade braking encounters physical limitations. First, the kinetic energy stored in a saw blade rotating at high speeds requires substantial braking force, which cannot be exerted without damaging the saw blade to avoid certain accident situations. This is particularly true when using large saw blades, whose large moment of inertia causes the saw blade to store too much energy for soft braking. The inventors have discovered that in a typical panel saw application, the braking force required to brake a 550 mm diameter saw blade with a braking time of 10 ms is approximately 1500 kW, while the braking force required to brake a 250 mm diameter saw blade is only approximately 300 kW, even though the smaller saw blade is driven at approximately twice the speed of the larger saw blade.

[0010] It has been proposed at various times to lower the saw blade in a rapid motion, instead of braking it, thereby bringing it into a position below the workpiece support surface and thus preventing any part of the user's body from coming into contact with the saw blade. However, here too, a large mass must be moved in a very short time, and in particular with a very high initial acceleration, which entails problems in terms of the generation of energy and forces for such acceleration, as well as in terms of the load on all the guide and bearing parts of the panel saw.

[0011] A safety device also intended for use with circular saws is generally known from US 9,702,916 B2. In this case, a dangerous situation is recognized by calibration and SNR calculation. When a dangerous situation occurs, the motor is stopped and a locking mechanism of the cutting tool is applied to stop the circular saw blade.

[0012] WO2017 / 059 473 A1 discloses a method for detecting human tissue in the vicinity of a tool by recording periodic changes in capacitance.

[0013] A safety system for a circular saw is already known from US 2016 / 0279754 A9. Listed among alternative or additional detection means and active means are contact with or proximity to the saw blade as a criterion for detecting a dangerous situation, and saw blade stopping and lowering as active means in a dangerous situation.

[0014] A safety system for a circular saw is already known from WO 2016 / 145 157 A1, in which contact or proximity of a body part with the saw blade is registered by capacitive measurement. Here, proximity of a body part stops the motor, whereas contact ignites a pyrotechnic braking device. The detection of the dangerous situation is carried out capacitively.

[0015] WO2015 / 091 245 A1 discloses an optical detection system for recording skin tone and the proximity of a body part to a saw blade, which is calculated from the skin tone. The reaction mechanism is described as stopping or lowering the saw blade. A dangerous situation is detected by triggering criteria of the body part approaching below a certain distance or exceeding a certain approach speed.

[0016] It is already known from US 2014 / 0 090 948 A1 to determine a dangerous situation when a body part approaches a saw blade by recording the temperature by infrared light. The speed of the object is recorded, including the direction and speed of movement. Depending on the speed recorded in this way, it is decided whether the drive is stopped or the brake is activated.

[0017] WO2013 / 046 522 A1 describes a system that uses triple sensors to monitor a danger zone and stops the saw blade when an object enters the danger zone. Only objects that reflect electromagnetic waves to a certain extent are recorded, and an example is given of an RFID tag attached to the tip of the thumb of a work glove. In a dangerous situation, an alarm signal is output in parallel with the stopping of the saw blade.

[0018] WO 2014 / 164 964 A1 describes a workpiece record that records the type of material of the workpiece in order to optimize the resulting cutting parameters. The speed of the circular saw blade is adjusted based on these parameters. The workpiece is recorded by a material sensor along its geometric length in the cutting direction, and the speed is reduced at the end of the cut, thereby reducing the risk of splinters and the associated injury to the operator.

[0019] US 2011 / 0 226 105 A1 describes various safety devices for circular saws, both for detecting dangerous situations and for taking action when a dangerous situation occurs. It discloses various sensor systems for recognizing dangerous situations and describes various actions for avoiding the dangerous situation. These include stopping the saw blade, lowering the saw blade, forming a protective shield around the saw blade (airbag), and acoustic or optical signals. The lever shown in FIG. 16 is intended to cover the saw blade cut in a dangerous situation, but does not appear to be a reliably effective safety device from a technical standpoint when the tool engages the workpiece.

[0020] US2009 / 0 301 275 A1 discloses a method for detecting body parts using electromagnetic waves with wavelengths between 400 nm and 1500 nm, and for preventing dangerous situations by covering and stopping the saw blade. The document also describes detecting a hand within a dangerous area as a trigger event.

[0021] A panel saw safety system in which rapid lowering of the saw blade is also implemented as a safety measure is already known from EP 3 403 762. In this system, the sawing unit with the attached saw blade is held in position by powerful magnets and against a pretensioning spring. When the safety device is activated, the polarity of these magnets is reversed, resulting in a vertical downward acceleration of the sawing unit. In principle, this system can be used to rapidly lower the saw blade, but the need for functional components such as magnets and pretensioning springs increases the mass of the sawing unit that must be moved for rapid lowering. As a result, considerable kinetic energy is generated during lowering. This results in significant loads on all bearing elements and guides of the panel saw, despite the complex buffering mechanism. This can cause the safety system to fail after a certain number of activations and can affect the precision and accuracy of the panel saw.

[0022] A safety device for a circular saw with a stopping or lowering of the circular saw blade is already known from DE 10 2007 062 996 A1. A dangerous situation is recognized by recognizing a body part and its direction of movement in the dangerous area, and separately the observation and comparison of two different movements is described.

[0023] DE 10 2008 001 727 A1 describes a protection device which in principle involves detection by a sensor, in particular a distance sensor, and an action which lowers the saw blade into a protection position.

[0024] DE10 2009 054 491 A1 describes a safety device for a circular saw that shuts down when the operator's specially designed gloves are detected. The position of the gloves is determined by recording electromagnetic radiation in the ultraviolet range, and when the gloves enter the danger zone, a guard covers the circular saw blade.

[0025] DE20 2010 004 458 U1 describes a safety system in which a sensor system records body parts in the front entrance area. The recognition of dangerous situations is carried out according to the standard, and the actions taken to prevent the dangerous situation include shielding the circular saw blade or lowering the saw blade below the table.

[0026] DE20 2011 101 566 U1 describes a device for quickly lowering a circular saw blade to avoid dangerous situations.

[0027] To date, none of the systems presented in these feasibility and fundamental studies have been shown to be viable for use on any type of circular saw, including professional panel saws, and have not been put into practical use. The inventors have discovered that there are several reasons for this. First, for use on any type of circular saw, particularly on commercial panel saws, a safety system must have high user acceptance, judged first in terms of operational safety and second in terms of operational efficiency. A safety system that significantly slows the work process, operates unreliably because it does not recognize typical hazardous situations that arise in professional use, or repeatedly erroneously operates because safe operating procedures are mistakenly recognized as hazardous situations, cannot be used on professional panel saws because, due to a lack of user acceptance, it will either not be purchased at all or will fail during everyday use after the initial experience of a defect.

[0028] Furthermore, professional panel saw users expect safety systems to be inexpensive to operate, especially when the system operates preventatively by activating in the event of a dangerous situation and allowing the panel saw to be quickly restarted after the protective device has been activated.

[0029] A typical requirement for all circular saws, especially professional panel saws, is that the safety system must function to accommodate all the various uses of the circular saw. This includes, among other things, the use of large saw blades at high speeds, sawing through very thick solid wood and boards, sawing through a variety of materials including light metals, working with or without gloves, and operating the panel saw with multiple users. Panel saw safety systems must be designed to address typical accident scenarios that occur on panel saws; a transfer from a system that reduces the risk of accidents on, for example, a table saw is already impossible due to the very different operator working postures and the way the workpiece is guided (two hands on one side of the saw blade for a panel saw, and two hands on both sides of the blade for a table saw).

[0030] Finally, a safety system suitable for use on a circular saw must also function reliably, even during rapidly repetitive work processes that often last hours or even an entire day while the saw is in operation, so that the protective system can obtain the approval that is customary or required in many countries by professional organizations, such as industry associations or certification bodies. Summary of the Invention

[0031] Against this background, the object of the present invention is to propose a circular saw, in particular a panel saw, suitable for professional use of the circular saw, with a system for protecting the operator from injuries on the saw blade. The present invention also proposes an improved protection system for protecting the operator from injuries during situations where there is a risk of injury (here understood as use, setup, maintenance or cleaning) in machine tools where there is a risk of injury, i.e. where the operator's hands may come into close proximity to tools that are at risk of injury during operation. Such machine tools may in particular be machine tools for material removal, shaping or reshaping processes, such as band saws, milling machines, lathes, electrical discharge machines, folding machines, bending machines, casting systems such as injection molding machines, cutting machines or welding machines.

[0032] This object is achieved according to the invention by a circular saw comprising: The circular saw includes: a support surface for a workpiece having a saw blade slot; a main drive motor arranged below the support surface for rotating the saw blade; a saw blade holder connected to the main drive motor for transmitting the rotational motion, the saw blade holder comprising a saw blade bearing unit and a saw blade flange mounted by the saw blade bearing unit so as to be rotatable about the saw blade axis and designed to be connected to the saw blade so as to be fixed under tension; a height adjustment device comprising a height actuator and a transmission element connected to the saw blade holder, the height adjustment device being arranged and designed to set the spacing between the saw blade holder and the support surface; an electronic interface for inputting a protruding height of the saw blade; a control device connected by signals to the electronic interface and the height actuator, and designed to operate the height actuator so that the protruding height of the saw blade input via the user interface is set by the height actuator; and a protection device for rapidly lowering the saw blade in a dangerous situation, the protection device being connected by signals to the monitoring device and the height actuator, and designed to operate the height actuator to rapidly lower the saw blade holder when a dangerous situation is recorded by the monitoring device.

[0033] The circular saw proposed according to the present invention is characterized by the fact that the saw blade is rapidly lowered by an actuator, and for this purpose, the same actuator, i.e., a height actuator, is used, which also serves to set a specific working height of the saw blade during normal operation. It is known in principle that the protrusion height of the saw blade above the workpiece support surface can be set for circular saws, and in some modern circular saws, this is also possible by motorized adjustment using a height actuator. As a result, the saw blade can be moved to the ideal protrusion for high-quality cutting of workpieces of a certain thickness. Various drives can be used as height actuators. It is customary and well-known that the height of the saw blade is set by an electric drive, e.g., an electric motor, which sets the height of the saw blade via mechanical elements, raising and lowering the saw blade unit and bearing.

[0034] According to the present invention, the height actuator serves both to set the protrusion height of the saw blade above the workpiece support surface and to rapidly lower the saw blade below the table in a dangerous situation. For this purpose, the height actuator is activated by both the circular saw's control device, which sets the protrusion, and the protection device, which activates the height actuator for rapid lowering of the saw blade. Setting the protrusion height of the saw blade and rapid lowering of the saw blade should be understood to mean that the entire saw blade unit, including, for example, the saw blade's bearing around the saw blade axis and, if necessary, the drive that rotates the saw blade, is adjusted in height and rapidly lowered when the safety system is activated. In other designs, it is also possible for only a portion of the saw blade, such as the saw blade's bearing unit, to be raised and / or lowered.

[0035] In the case of a circular saw according to the present invention, the use of a height actuator for rapid lowering avoids, on the one hand, the need to install additional components to achieve rapid lowering. It also avoids the need to decouple the height setting from such additional components so that rapid lowering can be performed with a separate safety actuator, thereby avoiding the need to operate against the height actuator required to set the protrusion height. Another advantage is that activation of the height actuator allows for direct control of the lowering of the saw blade from the working position to the safety position, while simultaneously controlling the movement with the assistance of the height actuator. These advantages are achieved because the height actuator, with its necessary precise actuation, provides corresponding control for precise height setting. The inventors have discovered that the height actuator can also be designed and operated so that both a strong initial acceleration and controlled braking of the lowering movement are achieved by the height actuator. As a result, rapid lowering significantly reduces the load on the circular saw, and rapid lowering does not result in damage to the precision bearings and guides of the circular saw, even when using large saw blades with a diameter of up to 550 mm or more.

[0036] A saw blade holder is understood as a rotatably mounted fixing option for a saw blade that has the necessary properties for guiding and torque-transmitting anchoring of the saw blade. The saw blade holder includes a saw blade bearing unit configured as a plain bearing, a rolling bearing, or other bearing to allow the saw blade to rotate about the saw blade axis. It also includes a saw blade flange that is rotatably mounted about the saw blade axis by the saw blade bearing unit and serves to hold the saw blade. The saw blade flange can be specifically designed here to hold the saw blade by clamping, screwing, or other positive locking means. This can be done, for example, by clamping the saw blade between two flange discs, by fixing the saw blade in a bayonet connection, or by screwing the saw blade in with several screws, etc.

[0037] The height adjustment device comprises, on the one hand, a height actuator and, on the other hand, a transmission element, where a height actuator is understood here as an electric drive element, for example an electric motor, a fluid drive, etc. A mechanical element, such as a spindle drive, a piston rod, a lever linkage, etc., which converts the movement caused by the height actuator into a height adjustment of the saw blade holder, serves as the transmission element.

[0038] The circular saw further includes a controller connected to an electronic interface for inputting the saw blade projection height. The electronic interface can be a user-operable input device, such as a keypad, touch screen, or voice recognition unit, or can be configured as a data interface for remote transmission of operating parameters. The controller generally comprises an electronic control system programmed to control various functions of the circular saw. According to the present invention, the controller is designed to operate a height actuator to set an appropriate saw blade projection height based on at least the projection height input via the interface or parameters from which such projection height can be derived.

[0039] The protective device according to the invention helps to quickly lower the saw blade in a dangerous situation, thereby preventing contact between the saw blade and parts of the user's body. A component of the protective device is a monitoring device that records dangerous situations. This monitoring device can have various designs, for example, it can be configured as an optical monitoring device that records the area around the saw blade with a capture device and determines the movement of the body part and its dangerous position by image evaluation. Other options for the monitoring device can include a capacitive sensor or an infrared sensor located adjacent to the saw blade to detect the approach of a body part.

[0040] If a dangerous situation is identified by the monitoring device, rapid lowering of the saw blade can be controlled by the height actuator as a direct measure, or possibly as a downstream measure prior to a first or further measure, such as a warning, first safety measure, etc. For this purpose, the height actuator is typically activated to strongly accelerate the saw blade vertically downward. Once the saw blade has been lowered and the danger has been eliminated, this rapid vertical movement can be braked again by a corresponding activation of the height actuator to mitigate the downward movement with the assistance of the height actuator. After the lowering has been performed and the dangerous situation has been eliminated, the height actuator can be activated again to raise the saw blade to its original sawing position. As a result, rapid restoration of the working position of the circular saw after the safety activation is achieved without the need for additional components or adjustment devices, and the safety activation does not cause any unnecessary delay in the working process of the circular saw.

[0041] According to the present invention, the actuation of the height actuator is performed by the circular saw's control unit on the one hand and the circular saw's protective device on the other. The control unit can receive signals from the protective device, be an integral part of the protective device, or part of the control unit can be an integral part of the protective device. In principle, control tasks on the circular saw, both in terms of setting normal operating parameters and implementing protective measures to avoid accidents, can be performed by a central control unit or by two or more separate, possibly redundant, control units. The protective device can also include an evaluation unit, which, among other things, detects and evaluates potential dangerous situations. Such an evaluation unit can be formed, for example, by two separate computer units to perform independent and autonomous monitoring functions.

[0042] According to the present invention, on the one hand, the setting of the protrusion height of the saw blade above the workpiece support surface as a normal operating parameter is performed by the height actuator, and on the other hand, the rapid lowering of the saw blade is also performed by the height actuator. It should be understood that this rapid lowering is performed at a higher movement speed of the saw blade than when setting the protrusion height of the saw blade. This is advantageous for both the required objectives, i.e., on the one hand, accurate setting of the desired protrusion height and on the other hand, the quickest possible lowering of the saw blade, and also helps to handle the components of the circular saw gently, since unnecessarily high accelerations are avoided during the process of setting the normal operating parameters, in this case the protrusion height of the saw blade. For the rapid lowering of the saw blade, the protective device thus activates the height actuator at a higher movement speed than for reducing the protrusion height of the saw blade by actuation from the circular saw control device during the process of setting the operating parameters during normal operation.

[0043] According to a first preferred embodiment, the height actuator is an electric servomotor. The inventors have found that an electric servomotor, which is a component of a servodrive, is suitable for ensuring precise setting of the protruding height of the saw blade, while also being able to apply the power required for rapid lowering of a large saw blade to a safe position. The servomotor preferably serves as a transmission element via a spindle drive. Such a spindle drive advantageously converts the rotational movement of the servomotor into the translational movement required for raising and lowering the saw blade holder. This translational movement is suitable for both precise setting of a specific height and high acceleration for rapid lowering.

[0044] According to a further preferred embodiment, the protection or control device activates the height actuator in a first operating mode to set the protruding height of the saw blade, activates the height actuator in a second operating mode to rapidly lower the saw blade, activates the height actuator in a third operating mode, preferably to return the saw blade to its original protruding height after rapid lowering, and in a fourth mode, preferably to set the height actuator to set the blade changing position, the circular saw further having a braking device for frictionally or positively fixing the blade changing position, and the protection or control device is further designed to activate the braking device after the blade changing position has been set by the height actuator to fix the blade changing position.

[0045] According to this advancement, the circular saw is designed to operate the height actuator in two different operating modes. In the first operating mode, the protruding height of the saw blade is set, and the height actuator is activated to precisely position the saw blade shaft at a specific height. In the second operating mode, the height actuator is activated to rapidly lower the saw blade. Here, the control objective is not to precisely position the saw blade shaft at a specific height, but to lower the saw blade in the shortest possible time to avoid injury to the user. Therefore, the speed of movement of the height actuator in the second operating mode is greater than the speed of movement in the first operating mode. In particular, the height actuator can be operated at maximum power in the second operating mode to achieve rapid lowering. Furthermore, in the second operating mode, the downward acceleration of the height actuator can be controlled, and the height actuator can be activated to brake the lowering motion and prevent a strong impact at the end of the motion.

[0046] Preferably, a third operating mode is also provided, in which the height actuator, after the rapid lowering, returns to the normal operating state with the saw blade at the same protruding height as before the rapid lowering. In this third operating mode, the previously stored position of the saw blade shaft is again approached. This approach occurs in the same manner and at the same speed as in the first operating mode. In this third operating mode, the circular saw is immediately returned to the normal operating state after the rapid lowering, allowing the operator to continue sawing with the circular saw.

[0047] Finally, a fourth operating mode is preferably provided in which the height actuator is driven to activate the blade change position. In this fourth operating mode, the brake device is additionally activated as soon as the saw blade reaches this blade change position. The blade change position must allow the user to remove the saw blade from the saw blade holder and secure another saw blade to the saw blade holder. This is typically done with the saw blade holder in a lowered position. In principle, the height actuator can be designed to controllably maintain a specific position, thereby resting the saw blade shaft at a specific height. Such a controlled position allows the protruding height of the saw blade to be set and maintained, for example, in the first operating mode. In particular, initiating and maintaining such a position is possible, for example, by using a servo motor as the height actuator.

[0048] In the blade change position, operating in the fourth mode, the user must grasp and remove the saw blade. For safety reasons, to avoid injury due to control errors in the height actuator's positioning, it is preferable to fix this position not by means of controlling the height actuator, but by a braking device separate from the height actuator. The braking device can act frictionally on the height actuator, a transmission element such as a spindle, or other guide element that guides the saw blade in vertical adjustment to fix the position of the saw blade axis. Alternatively, a positive braking device can be provided that actually mechanically locks the saw blade in the change position.

[0049] According to a further preferred embodiment, it is provided that the saw blade holder and the saw slot are designed to receive a saw blade having a diameter of 350 mm or more, preferably 400 mm or more or 450 mm or more, and that the protection device is designed to activate the height actuator and actuate the saw blade in the event of a rapid lowering from a position with an original protrusion height above the support surface to a lowered position with a final protrusion height of the saw blade above the support surface that is smaller than the original protrusion.

[0050] It should be understood that, according to the invention, this embodiment can essentially be configured independently of whether the protection device activates the height actuator or not. Equally effectively and alternatively, instead of the height actuator, another type of actuator can be activated to provide rapid lowering. In this case, the circular saw would have two independent actuators, one responsible for setting the protruding height of the saw blade and the other responsible for realizing rapid lowering of the saw blade.

[0051] This aspect of the present invention is based on the inventors' discovery that when the diameter of the saw blade exceeds 350 mm, 400 mm, 450 mm, or 500 mm, rapid lowering of the saw blade completely below the workpiece support surface is often impossible due to structural or power limitations. Depending on the size of the circular saw and the structural design of the saw blade unit, a problem arises in that complete lowering of the saw blade becomes impossible once a certain maximum size is exceeded. The problem here is not only that rapid lowering is not well-suited to achieving complete lowering purely geometrically, but also that when lowered to the maximum possible geometric limit, a hard impact can terminate the rapid lowering, potentially damaging the circular saw due to its high inertia, especially in the case of large saw blades. However, the inventors recognize that these limitations are not a reason to disable the protective device for larger saw blades or to limit circular saws with corresponding accident prevention features to saw blades below the maximum size.

[0004] The inventors have discovered that, on the one hand, due to the circular contour of the circular saw blade, in the case of vertical lowering, a distance between the body portion horizontally approaching the saw blade and the saw blade contour that is greater than the distance lowered by the saw blade shaft is already generated by the initial distance covered vertically by the saw blade shaft. This results from the arrangement of the saw blade shaft below the workpiece support surface and the resulting orientation of the tangent around the circumference of the circular saw blade.

[0052] This "conversion" can be understood as converting a small vertical downward movement into a large horizontal distance, allowing the horizontal distance between the body part approaching the saw blade and the outer periphery of the saw blade to be changed quickly enough to avoid an accident, even in the case of a large saw blade. At the same time, the rapid descent clearly alerts the user to the danger and prompts them to change or stop the dangerous movement of the body part, thereby reliably avoiding an accident in many cases. A partial descent can also be used to brake before the end of the geometrically determined movement using the descent actuator, in particular the height actuator, to avoid a strong impact at the end of the movement.

[0053] In particular, it is preferred to connect the partial lowering movement of a large saw blade with a simultaneous rapid braking of the saw blade rotation, so that the saw blade initially forms a horizontal distance from the body part, thereby avoiding injuries due to the partial rapid lowering, and when the partial lowering state of the circular saw blade is reached, it can be achieved that the saw blade is stopped from rotating so as to avoid serious cut injuries even when a body part comes into contact with the saw blade.

[0054] According to a further preferred embodiment, it is provided that the protection device is designed to activate the height actuator for rapid lowering in an acceleration phase in which the saw blade holder is accelerated downwards to the lowering speed, and then in a braking phase in which the saw blade holder is braked from the lowering speed.

[0055] According to this embodiment, the movement of the circular saw blade during rapid descent includes at least two phases. In the first phase, the saw blade is accelerated vertically downward by the height actuator, thereby accelerating from a standstill to a downward velocity. After this acceleration phase, or possibly immediately after this acceleration phase, the height actuator is activated by a protective device for a braking phase. In this braking phase, the height actuator slows the downward movement to prevent a strong impact at the end of the downward movement. In this braking phase, the saw blade holder can be controlled to brake and stop before the end of its movement. Alternatively, the braking phase can be controlled so that when the end of the movement is reached, the saw blade holder still has residual speed that is absorbed by a corresponding stop device, damper, buffer, or the like. The transition between the acceleration phase and the braking phase can be performed by a time control system or a movement control system, and a constant speed phase can also be provided between these two phases. In principle, the braking phase is initiated when the saw blade no longer protrudes above the workpiece support surface, i.e., when it has completely descended below the workpiece support surface. However, for large saw blades, the braking phase can also begin while the saw blade is still protruding above the workpiece support surface to avoid a strong impact at the end of travel, especially if the saw blade is so large that it does not descend completely below the workpiece support surface.

[0056] It is further preferred that the protective device is designed to activate the height actuator for transition from the acceleration phase to the braking phase as soon as the deceleration calculated from the calculated braking distance and the current descent speed of the saw blade exceeds a predetermined maximum deceleration (where the calculated braking distance is calculated by subtracting the current descent depth from the predetermined maximum descent depth of the saw blade), or as soon as the calculated braking distance is less than 50 mm (where the calculated braking distance is calculated by subtracting the current descent depth from the predetermined maximum descent depth of the saw blade), and / or as soon as the saw blade axis is below the support surface by a distance of at least half the diameter of the saw blade, if the height adjustment device has an adjustment travel at least 50 mm greater than half the diameter of the saw blade.

[0057] According to this embodiment, the transition from the acceleration phase to the braking phase is initiated according to three alternative criteria. It is understood that in one alternative embodiment, only one of these three criteria is implemented in the control system, and the transition between the acceleration phase and the braking phase is set only according to this alternative. In a second alternative embodiment, two or all three criteria are stored in the control system, and the calculation of when the transition from the acceleration phase to the braking phase will occur is performed synchronously during descent or with the help of pre-specified geometric values ​​such as the saw blade diameter, the saw blade protrusion height, and the maximum travel distance. In this second alternative embodiment, the braking phase is initiated as soon as one of the criteria is met.

[0058] While the calculated braking distance limit can be 50 mm, it should be understood that other limits, such as less than 25 mm, 30 mm, 40 mm, 60 mm, 70 mm, 80 mm, 90 mm, or 100 mm, can alternatively be used, depending on the design of the height adjustment device. Furthermore, the braking distance limit can be determined depending on parameters such as the diameter or weight of the saw blade, so that a variable limit is used to account for the kinetic energy generated when the saw blade is accelerated downward. This criterion ensures that, under typical operating parameters of a circular saw, i.e., typical circular saw blade diameters and blade projection heights, a sufficiently gradual braking of the rapid descent from the acceleration phase is achieved, thereby avoiding damage to the circular saw's guides and bearings caused by the rapid descent.

[0059] The present invention has been described above with respect to the rapid lowering of a circular saw blade using a height actuator. It should be understood that the present invention and the above-described aspects of the movement control, in addition to their application to circular saws, can also be used with other machine tools, where, if a dangerous situation for an operator caused by the tool is identified, the tool, which poses a risk of injury, must be removed from the danger zone as quickly as possible. In the case of such other machine tools, actuators provided for purposes other than tool setting, feed, or advancement, can also be advantageously activated for the rapid safe movement of such a tool to a safe position, appropriately designed to perform both an accurate tool setting operation and a rapid safe movement. Thus, for example, a milling tool can be rapidly moved away from a danger zone and away from the operator.

[0060] In this sense, the present invention also includes a safety device for a machine tool, The device is - Tools that may present a risk of injury and - an adjustment actuator coupled to the tool to effect the movement of the tool required to machine the workpiece; - an electronic interface for inputting the tool position; - a control device connected by signals to the electronic interface and to the adjustment actuator and designed to operate the adjustment actuator so that the tool position input via the user interface is set by the adjustment actuator; - a monitoring device for recording dangerous situations and a protective device for initiating safety measures, such as quickly removing the tool in a dangerous situation, The protection device is preferably connected to the monitoring device and the adjusting actuator by a signal and is designed to activate the adjusting actuator for a rapid displacement movement of the tool when a dangerous situation is registered by the monitoring device.

[0061] The above and following descriptions apply equally to this aspect, where the adjustment actuator corresponds to the height actuator, the tool corresponds to the saw blade or saw blade holder, the tool position corresponds to the saw blade height, and the rapid displacement movement corresponds to the rapid lowering.

[0062] The protective device may also implement other safety measures, such as enclosing, shielding or stopping the tool movement, pretensioning, releasing or reducing pressure, for example in the case of machine tools that do not allow rapid displacement movements of the tool or where this does not result in a reduction in the risk, thereby reducing or completely avoiding the risk to the operator.

[0063] According to a further preferred embodiment or an independent further aspect of the present invention, it is provided that the protective device is designed to receive the saw blade diameter and the saw blade protrusion height via the input interface and to identify a danger area around the saw blade located within a monitoring area monitored by the protective device from the saw blade diameter and the saw blade protrusion height, wherein the control device specifies the danger area to be larger when the saw blade diameter is large than when the saw blade diameter is small and / or the control device specifies the danger area to be larger when the saw blade protrusion height is large than when the saw blade protrusion height is small, and the protective device is designed to determine within what period of time the user's hand will enter the danger area from the position and movement of the user's hand recorded by the protective device in the monitoring area, and to execute rapid lowering of the saw blade if the determined period is less than a predetermined warning time.

[0064] It should be understood that this embodiment can be configured in connection with the circular saw or machine tool described above, provided that the protection device is connected by a signal to the monitoring device and the height actuator and is designed to activate the height actuator for rapid lowering of the saw blade holder when a dangerous situation is registered by the monitoring device. However, in a similar and alternative manner, it may be configured differently, in which the protection device activates a separate actuator for rapid lowering, and in this case the height actuator does not perform the dual function of setting the saw blade extension height and rapid lowering, but instead only performs the setting of the saw blade extension height.

[0065] This advancement is based on the insight that the practicality and relevance of a protective device require that the number of malfunctions be minimized, while at the same time ensuring a sufficient degree of safety from cuts in all operating conditions. The inventors have identified the following parameters as influencing this: the saw blade diameter, which in other machine tools generally refers to the tool dimensions, and the saw blade protrusion, which in other machine tools generally refers to the tool position. The function will be explained below using the saw blade diameter and protrusion height as examples. Therefore, first of all, in actual use, tasks involving cutting guide movements, in which the user must pass their hand next to the saw blade and move it close to it, are often performed, for which reason smaller saw blades and smaller protrusion heights are generally used. In contrast, large saw cuts are often performed using large saw blades and large protrusions, resulting in high energy consumption and high pressure from the user. As a result, for delicate work using a small saw blade or blade projection height, the protective device will only need to trigger a rapid lowering when the body part is closer to the saw blade than when using a larger saw blade or blade projection height.

[0066] The inventors have further discovered that smaller saw blades and smaller saw blade overhang heights can be lowered more quickly and with less energy expenditure than larger saw blades and / or saw blades with larger saw blade overhang heights, due in part to the lower inertia of these saw blades and in part to the shorter distance these saw blades must be lowered to be fully hidden below the workpiece support surface. For the same reason, smaller saw blades and / or saw blades with smaller saw blade overhang heights can be lowered more quickly with the same energy expenditure than larger saw blades and / or saw blades with larger saw blade overhang heights.

[0067] To equip such a professional circular saw according to the present invention with a practical protective device, a monitoring area in which a user's body part, e.g., the user's hand, is recorded is monitored by the protective device, and a risk area of ​​variable size is defined within this monitoring area. This risk area describes a bounded space or bounded surface related to one or more risk locations, such as the teeth of the saw blade or the point where the circumference of the saw blade contacts the workpiece support surface or the upper surface of the workpiece. If monitoring of the user's body part determines that, starting from the recorded position, this body part moves into the risk area within a predetermined pre-warning time, this identification triggers a rapid descent. It should be understood that the risk area is essentially used as a direct injury triggering criterion for assessing a dangerous situation. This does not exclude the possibility, for example, of defining a larger pre-warning area within the monitoring area and using the calculated intrusion of a body part into this pre-warning area to generate a pre-warning signal in the context of a cascade reaction of the protective device. The invention essentially consists in defining the size of the danger zone depending on at least one dimension of the tool and / or depending on at least one distance of the tool from the fixed position at which the danger is avoided or reduced, so that the protective device according to the invention can ensure that the operator is not injured even in the case of large tools and / or when the tool is moved a long distance from the fixed position.

[0068] According to the invention, the danger zone is not in principle understood only in the sense of a physical space or a physical surface, but can instead also be implemented by a corresponding adaptation of the pre-warning time, which here represents a period that is compared with the calculated time that the body part will reach the danger point, and if this period is shorter than the pre-warning time, a rapid descent is triggered. In this alternative, starting from the danger point as defined above, the pre-warning time is adapted, for example, depending on the diameter and / or protruding height of the saw blade. Thus, in the first case, the definition of the space or surface defining the danger zone is selected to be larger when the saw blade diameter or protruding height is large than when the corresponding saw blade diameter or protruding height is small, in order to ensure the practical sensitivity of the protective device; in the case of an alternative definition of the danger zone, such geometric limits are not moved, and instead the advance warning time is increased when the saw blade diameter / saw blade protrusion is large, so that a rapid descent is already triggered if the current position and movement of the body part would result in contact with the saw blade within a longer time than would be set in the case of a small saw blade diameter or small saw blade protrusion.

[0069] In addition to the saw blade diameter and protruding height, other parameters can also be taken into account to adjust the size of the danger zone or the advance warning time. For example, the position, speed, and acceleration of the body part can be used to calculate when a body part will reach the saw blade or a danger point on the saw blade. The danger zone or advance warning time can be expanded or contracted accordingly to ensure a sufficient safety buffer. The angle between the tangent to the workpiece support surface or the periphery of the saw blade at a point above the workpiece and the workpiece support surface can also be determined and taken into account. This tangent angle affects the speed at which the horizontal distance between the body part and the saw blade changes, relative to the vertical descent of the saw blade. In principle, a large tangent angle is disadvantageous for the rapid creation of horizontal distance by the saw blade's descent, while a small tangent angle is advantageous because a large horizontal distance can already be created between the body part and the saw blade after a short descent. Therefore, the danger zone or advance warning time for a small tangent angle can also be selected to be smaller than for a large tangent angle. Finally, the speed of the saw blade can also be taken into consideration when determining the size of the danger zone or the advance warning time, especially in the case of large saw blades that cannot be lowered completely below the workpiece support surface, since the braking of the saw blade to a rotational stop can also be taken into consideration in the safety design for these large saw blades, and this braking process can be longer or shorter depending on the speed.

[0070] According to a further preferred embodiment, the saw blade holder is connected to the main drive motor by a multi-ribbed belt tensioned to a belt tension by a self-adjusting belt tensioning device, the main drive motor is a three-phase AC motor, and the control or protection device is designed to simultaneously brake the main drive motor for the purpose of rapid lowering by injecting DC current, injecting the braking DC current at a predetermined current level during an initial braking phase and reducing the braking DC current after a predetermined braking time, and the belt tensioning device is designed to set the belt tension to between 90% and 100% of the upper limit of a predetermined belt tension adjustment range.

[0071] This embodiment is suitable to serve as an extension of the embodiment in which the height actuator is activated by the protective device, or as an independent aspect representing an advantageous embodiment of the protective device when the protective device activates a separate actuator for rapid descent.

[0072] This embodiment provides for the saw blade rotation to be stopped in parallel, i.e., simultaneously, in advance, or with a delay, during rapid lowering. It also provides for the saw blade to be driven by the main drive motor via a multi-ribbed belt. This type of drive has proven effective in terms of transmittable speed and torque, as well as quiet operation. However, such multi-ribbed belts have the disadvantage that they can slip when particularly large torques are applied to the belt pulley, resulting in no torque transmission or only reduced torque transmission. Therefore, a self-adjusting belt tensioning device is provided that tensions the multi-ribbed belt to a belt tension that allows for powerful braking by injecting a braking current into the drive motor. As a result, there is no need to provide an additional brake on the circular saw; instead, braking force is introduced via the main drive motor by corresponding operation of the three-phase AC motor. It should be understood that this embodiment can also be applied to other machine tools and tools in which the tool is driven via a belt drive or otherwise via static friction, as is the case, for example, with band saws having such a transmission means between the tool itself (saw band) and a driven drum on which the saw band is looped, or to the further machine tools mentioned above.

[0073] More preferably, the level of DC current injected into the three-phase AC motor for braking purposes is reduced starting from an initial level after an initial braking phase, either after a preset braking time or when the speed of the main drive motor drops below a certain level. This reduction in braking DC current prevents the build-up of an enhanced braking effect due to slippage of the multi-ribbed belt throughout the braking phase, which would otherwise result in a significant reduction in braking torque transmission due to sliding friction between the multi-ribbed belt and the belt pulley compared to static friction typically present between the multi-ribbed belt and the belt pulley.

[0074] It is particularly preferred that the belt tension be set between 90% and 100% of a predetermined belt tension limit. Multi-ribbed belts generally have a predetermined upper belt tension limit, and should not be tensioned beyond this limit, as this may result in damage. The drive torque for operating a circular saw can generally be reliably transmitted at a belt tension of less than 90%, e.g., less than 85% or even less than 80% of this maximum belt tension. However, it is advantageous for the purpose of rapid braking of the saw blade if the multi-ribbed belt is tensioned more strongly and maintained in the above-mentioned range of more than 90% of the maximum belt tension by a tensioning device.

[0075] It is further particularly preferred if the protection device comprises a monitoring device with an image capture device and an image evaluation device, the image evaluation device being connected to the height actuator by means of a signal in order to activate the height actuator when a dangerous situation is identified for rapid lowering of the saw blade holder.

[0076] Such a monitoring device with an image capture device and an image evaluation device allows, on the one hand, reliable monitoring of the movements of body parts in the vicinity of the circular saw blade, and, on the other hand, particularly advantageous designation of the monitoring area and the monitoring zone can be carried out by calculating the pre-warning time, expanding or reducing the monitoring zone depending on different parameters.The monitoring device can in principle be used on all types of machine tools where there is a risk of injury, in particular in combination with and as part of protective devices of the above-mentioned type.

[0077] A further aspect of the invention is a circular saw comprising: a support surface for a workpiece having a saw blade slot, a main drive motor arranged below the support surface for rotating the saw blade, a saw blade holder connected to the main drive motor for transmitting the rotational movement, the saw blade holder comprising a saw blade bearing unit and a saw blade flange mounted for rotation about the saw blade axis by the saw blade bearing unit and designed to be connected to the saw blade in a fixed manner under tension, a monitoring device arranged and designed to lower the saw blade holder when a dangerous situation is identified by the monitoring device and for recording the dangerous situation, and a protection device for rapidly lowering the saw blade in a dangerous situation, the protection device comprising: a height adjustment device comprising a height actuator and a transmission element connected to the saw blade holder, the monitoring device comprising an image capture device and an image evaluation device, the image evaluation device being connected to the height actuator by a signal for actuating the height actuator when a dangerous situation is identified for rapid lowering of the saw blade holder.

[0078] According to this aspect, a circular saw with a protective device for preventing work accidents is proposed to prevent cuts to a user's body part. Here, image capture is performed to identify whether a body part is approaching the saw blade in a dangerous manner. For this purpose, the image capture device records and monitors a monitoring area, and when a body part is identified therein approaching a dangerous spot on the saw blade or a dangerous area around the saw blade based on the position, movement speed, and / or acceleration determined for the body part, the image capture device can activate a height actuator to quickly lower the corresponding saw blade.

[0079] It should be understood that this circular saw can basically be developed using the technical aspects and development means described above. Furthermore, it should be understood that this aspect of the present invention, in addition to its application to circular saws, can also be used in other machine tools in which dangerous situations caused by the tool must be identified for the operator. Consequently, the subject of the present invention is also a machine tool with a protective device for avoiding work accidents to prevent cuts to the user's body parts, in which image capture is performed to identify whether the body part is approaching the tool in a dangerous manner. For this purpose, the image capture device records and monitors a monitoring area, and if a body part is identified in this monitoring area approaching a dangerous spot on the tool or a dangerous area around the tool based on the position, movement speed, and / or acceleration determined for the body part, safety measures such as quickly removing / shielding / braking the tool can be triggered.

[0080] It is further preferred that the image capture device comprises a first camera and a second camera, and that the image evaluation device comprises a first image evaluation unit and a second image evaluation unit, the first camera and the second camera being arranged spaced apart from each other above the workpiece support surface of the circular saw or machine tool and each having a recording direction facing towards the workpiece support surface, the first camera being connected by a signal to the first image evaluation unit, the first image evaluation unit being designed to receive image data from the first camera and process the data by means of first evaluation software to identify whether a dangerous situation exists, the second camera being connected by a signal to a second image evaluation unit designed to receive image data from the second camera and process the data by means of second evaluation software to identify whether a dangerous situation exists, the first evaluation software being different from the second evaluation software and / or the first image evaluation unit being different from the second image evaluation unit.

[0081] According to this embodiment, the image capture device is formed by at least two cameras spaced apart from one another, each of which performs image capture of an area of ​​the workpiece support surface. The two areas captured by the two cameras can partially or completely overlap, or can be separated from one another and thus combine to form the entire monitoring area. The image evaluation device also comprises first and second image evaluation units, the first image evaluation unit being associated with the first camera and the second image evaluation unit being associated with the second camera. This results in independent image capture and evaluation using separate image capture units (cameras) and separate image evaluation units, which is advantageous because a failure or malfunction of one camera or one image evaluation unit does not render the entire protection device inoperable. In particular, if the immediate danger area around the saw blade is advantageously captured redundantly by both cameras, independent and redundant monitoring of this danger area can be achieved by the image capture device and the image evaluation device.

[0082] Here, it is particularly preferred that the first evaluation software has a first operating system running on the first image evaluation unit and a first image evaluation algorithm running on the first image evaluation unit, and the second evaluation software has a second operating system running on the second image evaluation unit and a second image evaluation algorithm running on the second image evaluation unit, and that the first image evaluation unit and the second image evaluation unit are different from each other, or the first operating system and the second operating system are the same from each other and the first image evaluation algorithm and the second image evaluation algorithm are different from each other, or the first operating system and the second operating system are different from each other and the first image evaluation algorithm and the second image evaluation algorithm are the same from each other, or the first operating system and the second operating system are different from each other and the first image evaluation algorithm and the second image evaluation algorithm are different from each other.

[0083] According to this development, the hardware, operating systems, and / or software of the two image evaluation units are different from each other to provide redundancy that guarantees reliability. To this end, the first evaluation software on the first image evaluation unit and the second evaluation software on the second image evaluation unit are different, and / or the first image evaluation unit or the second image evaluation unit is different from each other. This difference can be achieved in the hardware of the image evaluation device or in the software installed on the image evaluation device, i.e., the operating system or evaluation software, or both. This difference is advantageous because systematic errors that could cause misrecognition, failure, or partially inaccurate evaluation of a dangerous situation do not necessarily occur synchronously in both image evaluation systems in parallel. Instead, redundancy that increases the reliability of the evaluation is achieved by the different hardware and / or different software.

[0084] It is further preferred here that the image evaluation device is designed to evaluate image data from the monitoring area and image data from the danger area, the danger area being located within the monitoring area and including a danger spot where a user may be injured on the saw blade, and that surface units within the danger area are captured by the first camera or the second camera with a greater number of pixels than surface units of the same size within the monitoring area.

[0085] According to this advancement, different resolutions are achieved between the danger zone and the monitoring zone surrounding the danger zone by means of the camera design, camera placement, or camera sensor plane configuration. As a result, the amount of data to be evaluated for monitoring body parts within the monitoring zone and the danger zone is reduced, and the objects within the monitoring zone are imaged at a lower resolution than within the danger zone, thereby achieving the required resolution for each danger level. This allows for efficient and rapid image evaluation, thereby enabling risk analysis performed in real time by image evaluation, and thus ensuring accident prevention, even when multiple body parts within the monitoring zone or danger zone need to be evaluated simultaneously.

[0086] It is further preferred if the image evaluation device is designed to receive operating parameters of the circular saw or machine tool and to vary the size of the danger zone depending on the operating parameters of the circular saw or machine tool.

[0087] As explained above, the size of the danger zone can be expressed as the length of the advance warning time. This danger zone or advance warning time can be varied based on the operating parameters of the circular saw. For example, a larger danger zone or a longer advance warning time can be selected for a larger saw blade, a larger saw blade protrusion, and / or a higher saw blade speed than for a smaller saw blade diameter, a smaller saw blade protrusion, and / or a lower saw blade speed. Additional operating parameters can also be taken into account to adapt the size of the danger zone. For example, the motor current of the circular saw blade's drive motor can be used to determine the current cutting force of the saw blade, which is a measure of the pressure exerted by the user. Consequently, a larger pressure exerted by the user can be considered, particularly in relation to the risk of the user's hand accelerating quickly in the event of slippage, which increases the risk of injury. Consequently, the danger zone can be enlarged / the advance warning time can be extended as a preventative measure.

[0088] It is particularly preferred here that the operating parameters include the diameter of the saw blade used and the saw blade protrusion height of the saw blade used above the workpiece support surface, or corresponding parameters of the machine tool, and that the image evaluation device is designed to identify, from the saw blade diameter and the saw blade protrusion height, the entry points and / or exit points of the saw teeth located on the outer periphery of the saw blade into or from the workpiece support surface as danger points, and to arrange danger areas in a predetermined shape around one or both of the danger points.

[0089] According to this development, one or two danger points corresponding to the intersection of the circumference of the circular saw blade with the workpiece support surface are determined from specific operating parameters, namely the diameter of the saw blade used and the protruding height of the saw blade. Instead of the workpiece support surface, the workpiece top surface can also be used, which can be determined, for example, from the input workpiece thickness and the recorded position height of the guard placed on the workpiece. The danger points thus determined serve to accurately identify the danger area. Particularly for small saw blades or small protruding saw blades, this calculation can prevent a rapid lowering trigger from occurring when a hand approaches the saw blade in a non-hazardous situation, as would occur if the danger area were specified as a fixed surface area around the saw blade. Particularly for large saw blades, potentially with a large protruding saw blade above the workpiece support surface, this further enables precise identification of danger points and more accurate recognition of dangerous situations from there, resulting in fewer false triggers and more reliable triggering in the event of an actual dangerous situation. Finally, when the upper surface of the workpiece is used to identify the danger spot, accurate identification of the actual danger spot is achieved even when the saw blade is tilted, in which case this danger spot can be horizontally offset relative to the saw groove and located above the workpiece support surface.

[0090] It is further preferred that the operating parameters include the diameter of the saw blade used and the protruding height of the saw blade used above the workpiece support surface, and that the image evaluation device is designed to define a larger danger zone when the saw blade diameter is large than when the saw blade diameter is small, and / or is designed to determine the tangent angle between the tangent at the periphery of the saw blade at the workpiece support surface and the tangent angle to the workpiece support surface from the saw blade diameter and the protruding height, and that when the tangent angle is large the danger zone is defined larger than when the tangent angle is small.

[0091] According to this development, one, two, or three additional parameters are taken into account to determine the size of the danger zone. On the one hand, it is taken into account that a saw blade with a large diameter descends more slowly than a saw blade with a small diameter, and similarly, a saw blade at a position of large saw blade projection descends more slowly than a saw blade at a position of small saw blade projection. Furthermore, the tangent angle also plays a role in accident avoidance, because with a small tangent angle, a considerable horizontal distance is already formed between the body part approaching the saw blade and the danger point even when the vertical descent distance is small, whereas with a large tangent angle, the ratio between the horizontal distance and the vertical descent distance created between the saw blade and the body part is unfavorably small, so that even over the first few centimeters of the descent movement, a favorable large horizontal distance between the body part and the saw blade cannot be achieved.

[0092] It is further preferred that the image evaluation device is designed to identify a dangerous situation when the body part of the user recognized by the image capture device is positioned such that the guard is located between the part of the body part and the image capture device, in particular when the guard is located in the optical path between the first camera or the second camera of the image capture device and the part of the body part.

[0093] This embodiment provides that a rapid lowering is triggered as soon as the body part recognized by the image evaluation is located below the guard surrounding the circular saw blade, which is advantageous because, on the one hand, the body part is approaching the saw blade in a critical manner, and, on the other hand, further movement of the body part below the guard can no longer be reliably determined by the image capture device, so that the presence of a dangerous situation can no longer be reliably recognized.

[0094] It is further preferred that the circular saw includes a height-adjustable guard that is positioned above the workpiece support surface and partially surrounds the saw blade, the guard then being movable from a position above the saw blade slot to a position next to the saw blade slot, the image evaluation device is designed to identify the contour or part of the contour of a virtual guard when the guard is moved from its position above the saw blade slot, and the image capture device is designed to identify a dangerous situation when a body part of the user recognized by the image capture device is positioned such that the contour or part of the contour is located between a part of the body part and the image capture device, in particular when the contour or part of the contour is located in the optical path between the first camera or the second camera of the image capture device and the part of the body part, and it is preferred that the image evaluation device is designed to determine the position of the guard or the circular saw includes a position sensor that records the position of the guard.

[0095] Basically, the guard is intended to surround the saw blade when the circular saw is in use and only rise high enough to allow the workpiece to pass under the saw blade. However, in some applications, particularly when cutting hollow objects, it is unavoidable to rotate the guard away. This increases the risk of injury, and also removes the area immediately surrounding the saw blade from the guard's protection. Therefore, it is advantageous if, when the guard is rotated away, a virtual area is defined around the circular saw blade that corresponds to the area normally covered by the guard, and if a body part is positioned in this virtual area, a rapid lowering is triggered. This allows a body part to be immediately aware of a dangerous situation and avoid injury, even when the guard is in a remote position.

[0096] It is further preferred here in particular that the width of the virtual guard is greater than the area covered by the saw blade protruding above the workpiece support surface as seen by the camera. This development is particularly advantageous in the case of an inclined position of the saw blade, i.e., when the rotation axis of the saw blade is arranged non-parallel to the workpiece support surface, thereby making angled or miter cuts.

[0097] It is further preferred that the circular saw further includes a height-adjustable guard positioned above the workpiece support surface, partially enclosing the saw blade, and a guard height sensor designed to determine the height of the guard above the workpiece support surface, and the control device is designed to form a height comparison value based on a comparison of the guard height above the workpiece support surface determined by the guard height sensor with the saw blade protrusion height, and to output a warning signal if the height comparison value exceeds a predetermined height comparison threshold.

[0098] According to this embodiment, the height positioning of the guard and the saw blade protrusion height of the circular saw blade are compared by reading the two values ​​from the corresponding sensors. This comparison allows for a plausibility test to be performed, which helps to recognize whether the height position of the guard has been incorrectly adjusted, resulting in an excessively large gap between the top of the workpiece and the bottom edge of the guard. In such cases, a warning signal can be output to notify the user of the incorrect guard setting. To avoid a dangerous situation, the saw blade can be quickly lowered. This can particularly occur if the user does not correct the guard position despite the previous warning signal and instead continues sawing, which can be recognized, for example, based on the saw blade rotation or motor current.

[0099] According to a further preferred embodiment, the image capture device includes a first camera and a second camera, the first camera having a first image capture surface with a first area centroid located on a first side of the saw blade slot on the workpiece support surface, and the second camera having a second image capture surface with a second area centroid located on a second side of the workpiece support surface opposite the first side of the saw blade slot, and the spacing between the first area centroid and the saw blade slot is smaller than the spacing between the second area centroid and the saw blade slot.

[0100] According to this embodiment, image capture is performed using two cameras spaced apart from each other, each capturing a surface on the workpiece support surface and positioned to the left and right of the saw blade slot. This avoids as much as possible the field of view being obscured by the saw blade or a guard above the saw blade, while ensuring that the monitoring area and the danger area around the saw blade are properly captured by the image capture device. The centers of the two image capture areas are preferably located at different distances from the saw groove. This results in asymmetry in the camera placement and image capture direction, but this is not critical in terms of the possibility of an object obscuring the area between the workpiece support surface and the camera.

[0101] Here, it is further preferred that the first image capture surface and the second image capture surface overlap with an overlap region, the overlap region covering the saw blade slot and preferably having a surface size equal to or greater than 50% of the surface size of the first image capture surface.

[0102] The capture planes of the two cameras overlap, and this overlap area is located in the area of ​​the saw blade. This overlap allows reliable, redundant capture of the immediate danger area around the saw blade by both cameras. This configuration is provided in accordance with the present invention for circular saws, band saws, and other types of saws, as well as other machine tools where there is a risk of obscuration corresponding to the camera's field of view.

[0103] According to a further preferred embodiment, the protective device is designed to perform an initialization process in which the hands of each user of the circular saw or machine tool are recorded by the monitoring device, which initialization process must be performed at least once, preferably daily, before the first sawing or machining procedure to be performed, and the protective device performs a quick lowering of the saw blade or a safety measure if the monitoring device recognizes hands in the monitoring area that were not recorded in the preceding initialization process.

[0104] According to this embodiment, the protective device of the circular saw is configured, on the one hand, during an initialization process to record one or more user's hands that will be monitored by the protective device during subsequent use of the circular saw. This initialization process is necessary for reliable operation of the circular saw to avoid the possibility of a body part that cannot be reliably recorded by the protective device appearing in the monitoring area and the user or any additional users joining him / her mistakenly assuming that the protective device is performing the function of monitoring such body part. Therefore, if a hand that has not been recorded during the initialization process is recognized in the monitoring area, a warning signal is output or the saw blade is quickly lowered to avoid a dangerous situation with the hand not secured by the protective device.

[0105] It is further preferred that the protection device comprises an optical signalling device designed to emit a first signal when the protection device is in an operable state and / or when a hand is recognised that does not represent a dangerous situation, and to emit a second signal when a hand is recognised that is in a dangerous situation that, if further moved, is expected to develop into a dangerous situation within a time period of less than 1 second, in particular less than 0.5 seconds.

[0106] This advance is based on the insight that an essential prerequisite for the usefulness of a protective device is that the user can trust its functional capabilities and its current monitoring function, and that these functional capabilities and monitoring functions must be identifiable to the user, or that the protective device must be able to detect when it is not performing these functions. To this end, a corresponding signaling device is provided that notifies the user of an activated state or a recognized state in which the hand is not in a dangerous condition with a first type of signal, and signals a pre-warning stage indicating that the body part recognition and dangerous situation assessment are functionally activated with a second type of signal. As a result, the user is informed of an abnormality in the protective device. The signaling device can be formed, in particular, by an optical signal located on the guard of the circular saw. A further function of such a signaling device is that a third type of signal can be used to signal the rotating saw blade.

[0107] According to a further preferred embodiment or a further independent aspect of the present invention, the protective device is provided such that the hand recorded by the image capture device is converted into a two-dimensional hand projection onto the workpiece support surface, and the position of the hand projection, the movement speed of the hand projection, and the vector portion of the acceleration in the direction of the danger point are determined, thereby determining the hand position, the hand movement speed in the direction of the danger point, and the hand acceleration in the direction of the danger area, and from the projected position, the projected movement speed, and the projected hand acceleration, it is determined within what period the hand will reach the danger point, and if this period is less than a predetermined advance warning time, a rapid lowering of the saw blade or a safety measure is executed, the advance warning time being preferably predetermined from the protruding height of the saw blade above the workpiece support surface and / or the saw blade diameter.

[0108] It should be understood that this embodiment can be used independently of or in combination with a height actuator that operates both for height setting and rapid lowering. This embodiment is more independent of the machine tool design and is generally suitable for machine tools where there is a risk of injury.

[0109] In this embodiment, the presence or absence of a dangerous situation is determined based on the position of the hand on the workpiece support surface, the movement speed toward the danger zone, and the projection of the hand's acceleration toward the danger zone. To this end, a two-dimensional projection of the hand onto the workpiece support surface is recorded using a capture device, and an image assessment of the dangerous situation is determined based on this projection. The vector components of the movement speed and the acceleration of the projection of the hand toward the danger zone are determined. This danger zone can be, for example, the intersection of the periphery of the saw blade with the workpiece support surface, or the position where the saw blade is closest to the user, i.e., the position where the saw blade teeth enter the workpiece support surface from above. Two or more danger zones can also be calculated, such as the rear intersection between the periphery of the saw blade with the workpiece support surface, or, in some cases, the intersection between the periphery of the saw blade with the top surface of the workpiece being cut by the saw blade. If it is determined that the time it takes for the hand to reach the danger zone is less than a predetermined advance warning time, the saw blade is quickly lowered because, if the hand moves further, the saw blade would no longer be able to be lowered below the workpiece support surface before coming into contact with the hand. Here, the advance warning time can be predetermined within a fixed value range. However, the advance warning time can also be variably predetermined by using relevant parameters for calculating the advance warning time as the period during which the saw blade is lowered to avoid a hazard. These parameters can be, for example, the protrusion height and / or diameter of the saw blade above the workpiece support surface, since a larger saw blade diameter or a larger protrusion height requires a longer advance warning time than a smaller saw blade diameter or a smaller protrusion height in order to still reliably lower the saw blade to avoid cuts. Further parameters (additionally or alternatively) can be taken into account when calculating the advance warning time, such as the tangent angle between the saw blade circumference and the workpiece support surface at the intersection of the saw blade circumference and the workpiece support surface.Because horizontal spacing between approaching hands occurs more quickly when the saw blade descends vertically at a small tangent angle than at a large tangent angle, the advance warning time is calculated here as being longer for large tangent angles and shorter for small tangent angles.

[0110] Finally, it is further preferred that the circular saw has an emergency switch-off operating element connected to the protection device by a signal, and that the protection device is designed to perform a rapid lowering of the saw blade when the emergency switch-off operating element is activated and to stop all drive elements of the circular saw when the rapid lowering is complete.

[0111] Machine tools such as circular saws are generally equipped with emergency stop switches, which are routinely specified in many national health and safety regulations. Here, an emergency switch-off operating element is intended to ensure the shutdown of all structural elements of the circular saw that could potentially pose a danger to the user and, accordingly, to cut off the main power supply to the circular saw. However, potentially dangerous situations can often be prevented in practice by cutting off the main power supply only with a time delay, for example, when the saw blade is still rotating at a high rotational speed for a relatively long time after the drive motor has stopped. Therefore, it is preferable to connect the activation of the emergency switch-off operating element to a rapid lowering of the saw blade, which requires a corresponding energy supply to the actuators still required for this for a short period of time after activation of the emergency switch-off operating element. Therefore, according to this development, it is provided that the emergency shut-off operating element is not used to immediately shut down the entire circular saw, so that rapid lowering can no longer be performed, but instead, this shutdown is performed only after the saw blade has been rapidly lowered, thereby creating a particularly safe state of the circular saw in a particularly short time.

[0112] It should be understood that the circular saw according to the present invention can be particularly configured as a panel saw, for which the safety system according to the present invention is particularly well suited due to its fast cutting cycle, large saw blade diameter and protruding height, and high saw blade speed. However, the protective device according to the present invention is also suitable for other machine tools that present potential hazards. For example, it can be used for plunge saws, table saws, or miter saws, which are often used portable on construction sites in the building industry and where the protective device according to the present invention can be used advantageously due to the environmental conditions. It is also possible to use the protective device on processing machines in the food processing industry, such as band saws. Dangerous situations for the operator can be recognized with the help of the protective device according to the present invention, and the band saw can be quickly stopped as a protective measure, for example. [Brief explanation of the drawings]

[0113] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

[0114] [Figure 1] FIG. 1 is a perspective view of a panel saw according to the present invention, seen obliquely from above the front. [Figure 2] FIG. 2 is a plan view of the workpiece support surface of a panel saw, showing a schematic representation of the monitored and dangerous areas. [Figure 3] FIG. 3 is a cross-sectional side view showing the line of sight from the monitoring device. [Figure 4] FIG. 4 is a front view of the panel saw, showing the line of sight from the monitoring device. [Figure 5] FIG. 5 is a perspective view of the saw blade unit of the panel saw in an inclined position, seen obliquely from above and rear left. [Figure 6] FIG. 6 is a perspective view of the saw blade unit of the panel saw in a non-tilted position, seen obliquely from above and rear left. [Figure 7] FIG. 7 is a perspective view of the saw blade unit of the panel saw in the blade replacement position, seen obliquely from above and rear left. [Figure 8]FIG. 8 is a schematic side view of a panel saw with a large saw blade and a small saw blade, showing the small saw blade protrusion height. [Figure 9] FIG. 9 is a schematic side view of a panel saw with a large saw blade and showing a large saw blade protrusion height. [Figure 10] FIG. 10 is a schematic plan view of the workpiece support surface showing the danger points and the hand approaching the saw blade. DETAILED DESCRIPTION OF THE INVENTION

[0115] The basic structure of a panel saw will first be described with reference to Figure 1. The panel saw includes a machine base body 10 on which a workpiece support surface 20 is placed. A carriage 30 is mounted on the machine base body for horizontal translational movement. The upper surface of the carriage 30 is a component of the workpiece support surface 20 and is flush with the workpiece support surface 20. A cross-cut table 40, which can translate together with the carriage, is fixed to the carriage 30. A cross-cut fence 41 is tiltably and repositionably arranged on the cross-cut table and is mounted on length stops 42a, b for longitudinal displacement, thereby allowing the cutting angle and cutting length of the workpiece to be placed thereon to be set.

[0116] A saw groove 21 is arranged in the workpiece support surface 20, and a saw blade 50 extends vertically through the saw blade 50. The saw blade 50 is mounted so as to be rotatable about a saw blade axis located within the machine body 10 below the workpiece support surface.

[0117] A vertical support 60, to which a guard 70 is fixed via a first cantilever arm 71, is fixed to the machine body 10. The guard 70 surrounds the saw blade 50 from above, and the circumferential angle of the enclosure can be changed by adjusting the height of the guard. Furthermore, the guard can move laterally to follow the tilt of the saw blade around a horizontal axis lying in the sawing direction. On the one hand, the guard 70 serves to cover the saw blade 50 for safety during operation, and on the other hand, sawdust generated during cutting is sucked through the guard by an appropriate suction device.

[0118] A user interface 80 is arranged on a second cantilever arm 81. The user interface 80 includes a display 82 for displaying machine parameters, information about the sawing cut and the position of the workpiece on the workpiece support surface. Various operating units are further arranged on the operator interface 80, including, inter alia, an emergency stop button 83.

[0119] A monitoring system with two cameras 90a,b is located on a third cantilever arm 91. The monitoring system is positioned above the saw blade so that the cameras 90a,b view the periphery of the saw blade with their line of sight directed vertically downwards towards the workpiece support surface.

[0120] 2 shows a monitoring area 100 that is recorded by the cameras 90a, b and monitored by the evaluation device. The monitoring area 100 is rectangular and surrounds a danger point 101 located in its center. The danger point 101 is the intersection of the saw blade periphery at the leading edge of the saw blade facing the workpiece before cutting and the workpiece support surface, and is the point where the saw teeth located on the saw blade periphery usually enter the workpiece support surface from above. The monitoring area 100 includes a fixed part located on the machine body 10 of the workpiece support surface and a movable part located on the carriage of the workpiece support surface.

[0121] A similarly rectangular surface portion 102 around the circular saw blade defines a guarded area of ​​the workpiece support surface from the monitoring area. This area 102 is shielded by the guard and therefore cannot be monitored. If a body part registered in the monitoring area 100 enters this demarcated portion 102, this represents a dangerous situation and appropriate action will be taken, as described below.

[0122] The danger zones 103a-c are located entirely within the monitoring area, separate from the delimited area 102, and are arranged as circles surrounding the danger point 101. The size of the danger zone can be varied, as symbolized by the three dashed circles 103a-c in FIG. 2, one of which delimits the danger zone. The size of the danger zone, in this example the diameter of the circle delimiting the danger zone, is specified based on operational parameters and body part operational parameters and depends on both adjustable machine parameters, such as the diameter and protruding height of the circular saw blade, and constantly changing operational and use parameters, such as the position and type of movement of the operator's hands, as will be explained in more detail below.

[0123] It should be understood that other shapes may be used as alternatives to the illustrated rectangular shape of the monitored area and circular shape of the danger area, for example, curved, elliptical, figure-eight shaped, or other delimited areas.

[0124] FIG. 3 is a side view showing the viewing angles of two cameras 90a, b. As can be seen, each of the two cameras has a viewing angle 90a', 90b' with a line of sight perpendicular to the workpiece support surface 20, resulting in camera capture areas 91a, b. The camera capture areas 91a, b overlap at a central area 91c that includes the entire saw blade and saw blade slot 21. Because of the guard 70, within this overlap area 91c, only two areas on the left and right sides of the guard can be monitored by one of cameras 90a, b, while the small area 91b between them cannot be monitored by either camera. This area 91d represents a section of the monitoring area corresponding to the sectioned area 102 in FIG. 2, and a different monitoring method is applied.

[0125] The cameras 90a, b are arranged on the left and right of a saw blade plane 92 in which the saw blade lies in the case of a horizontally arranged saw blade shaft, on a camera axis 93 arranged perpendicular to this saw blade plane. In this way, the line of sight of the front camera 90a is closer to the saw blade plane in the cutting direction than the line of sight of the rear camera 90b, and therefore the two cameras are arranged asymmetrically with respect to the saw blade plane.

[0126] 4 shows the field of view of the cameras 90a, b in a front view. As can be seen, the cameras 90a, b are looking downwards along vertical lines of sight 90a", 90b", in each case. The camera axis 93 on which the two cameras are arranged is here located at a height approximately perpendicularly above the danger zone of the medium-sized saw blade, with a horizontal distance of approximately 150 mm in front of the saw blade axis. In the view according to FIG. 4, the workpiece is fed from the right side, guided through the saw blade 50 in the feed direction Z to the left, and cut. The vertical lines of sight 90a", 90b" are therefore offset forward with respect to the saw blade axis SBA, which is opposite to the feed direction Z. As a result, the cameras are shifted forward (to the right in FIG. 4) with respect to the saw blade axis SBA and therefore monitor a wider area in front of the saw blade than behind it.

[0127] FIG. 5 is a perspective view of a saw blade unit of a panel saw according to the present invention. The saw blade unit is essentially positioned below the workpiece support surface 20 within the machine body 10. The entire saw blade unit can be tilted about a horizontal-vertical imaginary tilt axis SA that extends in the sawing direction, longitudinally through the saw blade slot, and at the height of the workpiece support surface 20. As a result, the saw blade axis SBA, and thus the saw blade, can be tilted so that the path of the saw blade through the saw blade slot does not change at each tilt position. FIG. 5 shows the saw blade unit in a tilted position in which the saw blade axis is not parallel to the workpiece support surface and therefore does not move horizontally. In principle, the saw blade unit of a panel saw according to the present invention can be configured to tilt on one side or both sides. In the case of one-side tilting, the saw blade unit can be tilted in only one direction about the tilt axis, starting from a position with a horizontally positioned saw blade axis. In the case of bilateral tilting, the saw blade unit can be tilted in both directions about the tilt axis, starting from a position with a horizontal saw blade axis.

[0128] The saw blade unit further comprises a saw blade drive motor 110 having an output shaft to which a lower V-ribbed belt pulley is fixed, which is driven via a V-ribbed belt by an upper V-ribbed belt pulley fixed to a saw blade shaft 151. The saw blade shaft is mounted on a saw blade bearing unit 120 so as to be rotatable about the saw blade shaft. A saw blade flange 152 to which the saw blade 50 is fixed is further arranged on the saw blade shaft.

[0129] The entire unit consisting of the saw blade drive motor 110, saw blade bearing unit 120, and saw blade flange 152 is mounted so as to be vertically displaceable by a linear bearing consisting of two linear guide rails 140a, b fixed to the saw blade unit frame 130 and linear guide shoes guided by the rails. The protrusion height of the saw blade from the saw blade slot 21 above the workpiece support surface 20 can be set by this vertical displacement. Because the linear guides are fixed to the saw blade unit frame 130, which is tilted together with the saw blade unit, this setting can be set at each tilt position of the saw blade unit.

[0130] Furthermore, a servo motor 160 that drives a spindle drive device 161 is fixed to the frame 130 of the saw blade unit. The servo motor is fixedly attached to the saw blade unit frame 130. A spindle plate 162 that moves up and down as the spindle rotates along its longitudinal axis is guided on the spindle 161 driven by the servo motor. The saw blade bearing unit 120 and the saw blade drive motor 110 are connected to the spindle plate 162. Therefore, by driving the spindle 161, the saw blade bearing unit 120 can be displaced vertically along the linear guide rails 140a, b together with the saw blade drive motor 110.

[0131] The servo motor 160 is operated for such displacement purposes, on the one hand, to set the saw blade protrusion height desired by the user for the sawing procedure. This saw blade protrusion height is typically selected to be approximately the saw blade tooth height greater than the thickness of the workpiece to be cut when a separation cut is being made. In contrast, when a groove is being cut, the saw blade protrusion is set to be the same as the groove depth. To accurately set the saw blade protrusion height, the servo motor is operated at a slow setting speed, for example, about 5 cm / s.

[0132] The servo motor 160 can also be operated for rapid lowering. In this case, the servo motor serves to lower the saw blade in the shortest possible time to avoid dangerous situations caused by a body part approaching the saw blade and to prevent the approaching body part from being injured by the saw blade. In this case, the servo motor operates at a very high, particularly maximum allowable, driving force, thereby rapidly accelerating the saw blade downward. For such rapid lowering, the servo motor achieves a movement speed of the saw blade bearing unit of 0.5 m / s or more, particularly 1 m / s or more, and the servo motor and spindle drive are preferably designed to generate a lowering speed of 2 m / s or more or 4 m / s or more. As a result, the saw blade can be lowered at a sufficiently high speed to reliably prevent contact between the body part and the saw blade, even when the body part approaches the saw blade at high speed.

[0133] During rapid descent, the servo motor first operates to generate maximum downward acceleration of the saw blade bearing unit to which the saw blade is fixed. After a certain amount of travel, before reaching the end stop of the spindle drive, the servo motor is decelerated again, thereby braking the rapid vertical downward movement of the saw blade and saw blade bearing unit. This deceleration is performed by a negative acceleration, i.e., a braking acceleration, which is sufficient to decelerate the vertical downward movement of the saw blade and saw blade bearing unit, preferably to zero speed, but at least to a low speed, until the end of the spindle drive is reached. As a result, a strong shock at the end of the displacement movement is avoided.

[0134] FIG. 6 shows a perspective side view of the saw blade unit from the left, and FIG. 7 shows a perspective view of the upper part of the saw blade unit from the front, right, and top. A lower support plate 180 is fixed to the upper housing wall of the saw blade drive motor 110. A stack of compression springs 182, consisting of multiple leaf springs, is supported around a threaded bolt 181 extending vertically upward. The stack of compression springs supports an upper support plate 183, which is fixed to the saw blade bearing unit 120, with a compressive spring force. Therefore, the stack of compression springs 182 applies a biasing force to a V-ribbed belt 184 that moves between an upper belt pulley 185 attached to the saw blade bearing unit 120 and a lower belt pulley 186 fixed to the output shaft of the saw blade drive motor 110 (see FIG. 7). The V-ribbed belt 184 can be pretensioned to a high tension by loosening two screws 188a and 188b arranged in slots. This pretension can be fixed by tightening the two screws 188a, b and will not change over long periods of operation as the V-ribbed belt 184 will not stretch substantially.

[0135] 7 shows the saw blade bearing unit 120 in the blade change position. In this blade change position, the saw blade unit is lowered with the aid of the servo motor 160 and spindle 161 to a point where a saw blade having the largest allowable diameter can be removed from or placed on and clamped into the saw blade holder 190 attached to the saw blade bearing unit 120 so that it can rotate about the saw blade axis SBA. The blade change position is actuated by the servo motor 160 in response to a corresponding operator input and is locked by a locking brake (not visible) internal to the servo motor, thereby ensuring that the blade change position is maintained securely. This avoids the risk of injury to the operator when changing the saw blade.

[0136] 8 is a schematic diagram of two different sizes of saw blades 250a, b with a small saw blade protrusion height S1, showing the direction in which the workpiece is guided from right to left in the feed direction Z during sawing.

[0137] FIG. 9 is a schematic diagram of a large saw blade 250a having a large saw blade protrusion height S2.

[0138] As can be seen in Figures 8 and 9, different positions of the danger point, defined as the intersection of the saw blade circumference and the workpiece support surface at the front side of the saw blade, result from these different saw blade sizes and saw blade protrusion heights. The most forward danger point 260 occurs for the large saw blade 250a with the large saw blade protrusion height S2 (Figure 9). When the large saw blade is lowered to the small saw blade protrusion height S1, a second danger point 261 occurs behind this danger point 260 in the workpiece feed direction. If a small saw blade 250b is used instead of the large saw blade 250a, the danger point 262 of this small saw blade 250b with the same (smaller) saw blade protrusion height S1 is now shifted further in the workpiece feed direction Z.

[0139] Figure 10 is a schematic diagram illustrating the calculation of the user's hand position and movement. This calculation is performed by projecting the hand onto the workpiece support surface and by referencing an XY coordinate system centered at a point on the workpiece support surface that is vertically above the saw blade axis and located within the cutting plane. The Y axis here is parallel to the workpiece support surface and passes through the plane in which the saw blade axis is located at the desired title position. The X axis corresponds to the intersection of the workpiece support surface and the cutting plane.

[0140] In this case, the angle φ between the Y axis and the direction of hand movement Hand is calculated as follows:

number

[0141] Hand movement speed v Hand is calculated as follows:

number

number

number

[0142] Then, from these calculation data, the calculated hand velocity v Hand but the maximum velocity v can be preset as, for example, 2 m / s. max and whether the magnitude of the angle δ is less than or equal to a preset tolerance angle, which may be, for example, 30°, thereby identifying whether an injury to the hand on the saw blade will occur within a time shorter than the advance warning time required to lower the saw blade in time to avoid such injury.

number

number

Claims

1. In particular, a circular saw that is a panel saw, a support surface for the workpiece having a saw blade slot; a main drive motor disposed below the support surface for rotating the saw blade; a saw blade holder coupled to the main drive motor for the purpose of transmitting rotational motion, the saw blade holder comprising a saw blade bearing unit and a saw blade flange mounted for rotation about the saw blade axis by the saw blade bearing unit and designed to be coupled to the saw blade so as to be fixed under tension; a height adjustment device including a height actuator and a transmission element connected to the saw blade holder, the height adjustment device being arranged and designed to set a spacing between the saw blade holder and the support surface; an electronic interface for inputting the protrusion height of the saw blade; a control device connected by signals to the electronic interface and the height actuator and configured to operate the height actuator such that the protrusion height of the saw blade input via the user interface is set by the height actuator; a protection device for quickly lowering the saw blade in a dangerous situation, the protection device having a monitoring device for recording the dangerous situation; a protection device connected to the monitoring device and the height actuator by a signal, and designed to activate the height actuator to quickly lower the saw blade holder when a dangerous situation is recorded by the monitoring device; Circular saw.

2. the height actuator is an electric servo motor; 2. The circular saw of claim 1.

3. The protective or control device is in a first mode of operation, actuating a height actuator to set a protrusion height of the saw blade; in a second mode of operation, actuating the height actuator to rapidly lower the saw blade; In a third mode of operation, preferably, the height actuator is actuated to return the saw blade to its original saw blade extension height after the rapid lowering; In a fourth mode, preferably, actuating a height actuator to set a blade change position; The circular saw further comprises a braking device for frictionally or positively fixing the blade changing position, and the protection or control device is further designed to activate the braking device after the blade changing position has been set by the height actuator in order to fix the blade changing position.

3. The circular saw according to claim 1 or 2.

4. The saw blade holder and saw groove are designed to receive a saw blade having a diameter of 350 mm or more, preferably 400 mm or more, or 450 mm or more, and the protection device is designed to activate the height actuator and operate the saw blade in the event of a rapid lowering from a position having an original protruding height above the support surface to a lowered position having a final protruding height of the saw blade above the support surface that is smaller than the original protrusion. The circular saw according to any one of claims 1 to 3.

5. The protection device is designed to activate the height actuator for rapid lowering in an acceleration phase in which the saw blade holder is accelerated downward to a lowering speed, and then in a braking phase in which the saw blade holder is braked from the lowering speed. The circular saw according to any one of claims 1 to 4.

6. The protective device As soon as the deceleration calculated from the braking distance calculated by subtracting the current descent depth of the saw blade from the predetermined maximum descent depth of the saw blade and the current descent speed of the saw blade exceeds the predetermined maximum deceleration. or As soon as the braking distance calculated by subtracting the current descent depth from the predetermined maximum descent depth of the saw blade is less than 50 mm, and / or If the height adjustment device has an adjustment travel of at least 50 mm greater than half the diameter of the saw blade, as soon as the saw blade axis is below the support surface by a distance of at least half the diameter of the saw blade, designed to activate the height actuator for the transition from the acceleration phase to the braking phase, 6. The circular saw according to claim 5.

7. a protection device configured to receive a saw blade diameter and a saw blade protrusion height via an input interface, and to identify a danger area around the saw blade, which is located within a monitoring area monitored by the protection device, from the saw blade diameter and the saw blade protrusion height; the danger zone is designated by the control device to be larger in the case of a large saw blade diameter than in the case of a small saw blade diameter, and / or the danger zone is designated by the control device to be larger in the case of a large saw blade protrusion than in the case of a small saw blade protrusion, The protective device is designed to determine, from the position and movement of a user's hand recorded by the protective device in the monitoring area, within what period the hand will enter the danger area, and to execute a rapid lowering of the saw blade if the determined period is less than a predetermined warning time. Circular saw according to any one of claims 1 to 6 or the preamble of claim 1.

8. a saw blade holder connected to the main drive motor by a multi-ribbed belt tensioned to a belt tension by a self-adjusting belt tensioning device; The main drive motor is a three-phase AC motor, and the control or protection device is designed to simultaneously brake the main drive motor by injecting DC current for the purpose of rapid lowering, injecting the braking DC current at a predetermined current level in the initial braking phase and reducing the braking DC current after a predetermined braking time; The belt tension adjusting device is designed to set the belt tension between 90% and 100% of the upper limit of a predetermined belt tension adjustment range. The circular saw according to any one of claims 1 to 7.

9. the protection device includes a monitoring device having an image capture device and an image evaluation device; the image evaluation device is connected to the height actuator by a signal so as to activate the height actuator when a dangerous situation is identified for rapid lowering of the saw blade holder; The circular saw according to any one of claims 1 to 8.

10. The image capture device includes a first camera and a second camera, the image evaluation device includes a first image evaluation unit and a second image evaluation unit, It is further preferred that the first camera and the second camera are arranged spaced apart from each other above a workpiece support surface of the circular saw or machine tool, each having a recording direction pointing towards the workpiece support surface; the first camera is connected by a signal to a first image evaluation unit, which is designed to receive image data from the first camera and to process the data by means of first evaluation software in order to identify whether a dangerous situation exists; the second camera is connected by signals to a second image evaluation unit designed to receive image data from the second camera and process the data by means of second evaluation software in order to identify whether a dangerous situation exists; the first evaluation software is different from the second evaluation software and / or the first image evaluation unit is different from the second image evaluation unit, 10. The circular saw of claim 9.

11. The first evaluation software has a first operating system that operates on the first image evaluation unit and a first image evaluation algorithm that operates on the first image evaluation unit; the second evaluation software comprises a second operating system running on the second image evaluation unit and a second image evaluation algorithm running on the second image evaluation unit; the first image evaluation unit and the second image evaluation unit are different from each other; or the first operating system and the second operating system are the same, and the first image evaluation algorithm and the second image evaluation algorithm are different from each other; or the first operating system and the second operating system are different from each other, and the first image evaluation algorithm and the second image evaluation algorithm are the same from each other; or the first operating system and the second operating system are different from each other, and the first image evaluation algorithm and the second image evaluation algorithm are different from each other; 11. The circular saw of claim 10.

12. An image evaluation device is designed to evaluate image data from a monitored area and image data from a dangerous area; a danger area is located within the monitored area and includes a danger point where a user may be injured on the saw blade; The surface units in the danger zone are captured by the first camera or the second camera with a larger number of pixels than the surface units of the same size in the monitoring zone, so that a lower resolution is achieved in the monitoring zone than in the danger zone. Circular saw according to claim 10 or 11.

13. The image evaluation device is designed to receive operating parameters of the circular saw or machine tool and to change the size of the danger zone depending on the operating parameters of the circular saw or machine tool. The circular saw according to any one of claims 10 to 12.

14. The operating parameters include the diameter of the saw blade used and the saw blade protrusion height of the saw blade used above the workpiece support surface, or corresponding parameters of the machine tool; the image evaluation device is designed to identify, based on the saw blade diameter and the saw blade protrusion height, the entry points and / or exit points of the saw teeth arranged on the outer periphery of the saw blade into or from the workpiece support surface as danger points, and to arrange danger areas in a predetermined shape around one or both of the danger points; 14. The circular saw of claim 13.

15. The operating parameters include a diameter of the saw blade used and a saw blade projection height of the saw blade used above the workpiece support surface; The image evaluation device A larger saw blade diameter is designed to define a larger danger area than a smaller saw blade diameter; and / or The saw blade is designed to determine the angle between a tangent at the periphery of the saw blade on the workpiece support surface and a tangent to the workpiece support surface from the diameter of the saw blade and the protruding height of the saw blade; and, Large tangent angles are designed to define a larger danger area than small tangent angles; Circular saw according to claim 13 or 14.

16. The saw blade further includes a height-adjustable guard positioned above the workpiece support surface and partially enclosing the saw blade; the image evaluation device is designed to identify a dangerous situation when the body part of the user recognized by the image capture device is positioned such that the guard is located between the part of the body part and the image capture device, in particular when the guard is located in an optical path between the first camera or the second camera of the image capture device and the part of the body part; The circular saw according to any one of claims 9 to 15.

17. A saw blade cutting tool comprising: a height-adjustable guard positioned above the workpiece support surface and partially surrounding the saw blade; a guard movable from a position above the saw blade slot to a position adjacent the saw blade slot; the image evaluation device is designed to identify a virtual guard contour or a portion of a contour when the guard has been moved from its position above the saw blade slot, and is designed to identify a dangerous situation when a body part of a user recognized by the image capture device is positioned such that the contour or a portion of the contour is located between a portion of the body part and the image capture device, in particular when the contour or a portion of the contour is located in an optical path between a first camera or a second camera of the image capture device and a portion of the body part; The image evaluation unit is preferably designed to determine the position of the guard or the circular saw includes a position sensor which records the position of the guard, A circular saw according to any one of claims 9 to 16.

18. The saw blade cutting machine of claim 1, further comprising: a height-adjustable guard positioned above the workpiece support surface and partially enclosing the saw blade; and a guard height sensor configured to determine the height of the guard above the workpiece support surface; the control device is designed to form a height comparison value based on a comparison of the guard height above the workpiece support surface determined by the guard height sensor with the saw blade protrusion height, and to output a warning signal when the height comparison value exceeds a predetermined height comparison threshold. A circular saw according to any one of claims 9 to 17.

19. An image capture device comprising a first camera and a second camera; a first camera having a first image capture plane with a first area center of gravity located on a first side of the saw blade slot in the workpiece support surface; a second camera having a second image capture plane with a second area center of gravity located on a second side of the workpiece support surface opposite the first side of the saw blade slot; a distance between the first area centroid and the saw blade slot is smaller than a distance between the second area centroid and the saw blade slot; A circular saw according to any one of claims 9 to 18.

20. The first image capture surface and the second image capture surface overlap with an overlap region, the overlap region covering the saw blade slot and preferably having a surface size that is 50% or more of the surface size of the first image capture surface.

20. The circular saw of claim 19.

21. The protection device is designed to perform an initialization process in which the hands of each user of the circular saw or machine tool are recorded by a monitoring device, The initialization process must be performed at least once, preferably daily, before the first sawing or machining procedure is performed; The protection device will immediately lower the saw blade or take safety action if the monitoring device detects a hand in the monitoring area that was not recorded in the previous initialization process.

21. A circular saw according to any one of claims 1 to 20.

22. The protection device includes an optical signal device; The optical signal device emitting a first signal when the protective device is in an operational state and / or when a hand not representing a dangerous situation is detected; designed to emit a second signal when a hand is recognized as being in a dangerous situation where further hand movement is predicted to develop into a dangerous situation within a time period of less than 1 second, particularly less than 0.5 seconds; 22. A circular saw according to any one of claims 1 to 21.

23. The protection device, The image capturing device is designed to record the hand and convert it into a two-dimensional projection of the hand onto the workpiece support surface, and determine the position of the projection of the hand, the velocity of movement of the hand in the direction of the hazard, and the acceleration of the hand in the direction of the hazard area by determining the vector portion of the projection of the hand and the velocity of movement of the hand in the direction of the hazard area; From the projected position, the projected moving speed, and the projected acceleration of the hand, it is determined within what period the hand will reach the danger point; If the period is less than a predetermined advance warning time, a quick lowering of the saw blade or safety action is taken; The advance warning time is preferably predetermined from the protruding height of the saw blade above the workpiece support surface and / or the saw blade diameter. Circular saw according to any one of claims 1 to 22 or the preamble of claim 1.

24. An emergency switch-off operating element connected to a protection device by a signal, The protective device is designed to effect a rapid lowering of the saw blade when the emergency switch-off operating element is activated, and to stop all drive elements of the circular saw when the rapid lowering is completed.

24. A circular saw according to any one of claims 1 to 23.

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