Emergency brake assembly for a motor-driven tool and method for operating an emergency brake assembly

Description

[0001] The invention relates to an emergency braking assembly for a motor-driven tool.

[0002] Furthermore, the invention relates to a method for operating an emergency brake assembly.

[0003] Motor-driven tools with emergency braking assemblies are known from the prior art. The same applies to emergency braking assemblies. These serve to bring a cutting element, e.g., a saw blade, of the tool to a standstill if contact between a user and the cutting element is imminent or detected during operation. In this way, injuries are prevented or their severity is reduced.

[0004] In this context, actuators with actuating elements comprising a shape memory alloy can be used. The function of such actuators is based on a thermally activated lattice transformation of the shape memory alloy, which leads to a change in the length of the actuating element. An actuating element is thus understood to be that element of the actuator by means of which the movement is generated that the actuator needs to actuate a system actuated by the actuator, in this case the braking system or brake element. Actuating elements comprising a shape memory alloy are often shaped as wires that shorten due to the thermally activated lattice transformation.

[0005] Such actuators are preferably used in reversible emergency braking assemblies, i.e., in emergency braking assemblies that can be used multiple times to bring the cutting element to a standstill. It is understood that in reversible emergency braking assemblies, the actuator must be operable multiple times with consistently high reliability.

[0006] EP 3 772 398 A1 presents a braking device for a chainsaw and a method for protecting an operator. DE 10 2019 117 447 B3 describes an electromechanical braking device and a method for its operation. DE 10 2019 210 187 A1 deals with a tool device comprising a tool braking device for braking a tool's rotary motion. DE 10 2018 116 437 A1 discloses a brake with a wedge gear and mechanical energy storage device, as well as a method for its operation.

[0007] The invention is therefore based on the objective of further improving emergency brake assemblies whose actuating element comprises a shape memory alloy.

[0008] The problem is solved by an emergency braking assembly for a motor-driven tool, comprising a holding structure, a brake element rotatably mounted on the holding structure (in particular, a brake cam), and a wire-shaped actuating element made of a shape memory alloy. A first end of the actuating element is attached to the holding structure. A second end of the actuating element is coupled to the brake element for drive purposes. In this context, a wire-shaped actuating element is understood to be one that can essentially only be subjected to tensile stress, i.e., that can only transmit tensile forces. Under compressive stress, such an actuating element is unstable. Furthermore, the wire shape implies that the actuating element is much longer than it is wide. A wire-shaped actuating element made of a shape memory alloy is often referred to simply as a shape memory alloy wire or FMI wire.The holding structure is formed, for example, by an actuator housing (i.e., a housing of the actuator containing the actuating element), a brake caliper, or a combination thereof. The fact that the second end of the actuating element is coupled to the brake element means that the brake element can be driven via this coupling, i.e., it can be moved from a release position, in which the brake element has no braking effect, to a braking position, in which it does have a braking effect. Preferably, the movement of the brake element from the release position to the braking position is caused by a contraction or retraction of the actuating element. The actuating element thus drives the brake element. Such a configuration is simple and robust.In particular, such a configuration is structurally simpler than designs of emergency brake assemblies where only a movement release can be controlled by means of an actuating element comprising a shape memory alloy.

[0009] In summary, an emergency brake assembly is understood to be a combination of an actuator and a brake element. In this case, the actuator has an actuating element that comprises a shape-memory alloy. The brake element is, for example, a brake cam. Such an emergency brake assembly can be part of an emergency brake unit designed to brake a cutting element of a motor-driven tool to a standstill.

[0010] In the context of the present invention, a brake cam is understood to be a rotatably mounted brake element which is at least partially eccentric, so that the brake element can be moved by rotating from a release position in which the brake element has no braking effect to a braking position in which it has a braking effect.

[0011] It is understood that the actuating element may include insulating elements at its ends to electrically isolate the actuating element from the holding structure and / or the braking element.

[0012] In one example, the retaining structure is made of a plastic material. In this case, an insulating element at the first end of the actuating element is unnecessary.

[0013] According to an alternative design, the second end of the actuating element is attached to the brake element. In this alternative, the actuating element is therefore attached to both the mounting structure and the brake element. The brake element can thus be driven directly by the actuating element. Such a design is particularly simple and robust.

[0014] According to another alternative, the second end of the actuating element is coupled to the braking element via at least one intermediate element. This intermediate element is thus arranged between the braking element and the second end of the actuating element in such a way that the braking element can be driven by the actuating element and via the intermediate element. Such an intermediate element can, on the one hand, be used to bridge a geometric distance between the second end of the actuating element and the braking element. On the other hand, the intermediate element can also serve to convert a movement of the second end of the actuating element, so that the movement with which the braking element is driven can differ from the movement of the second end of the actuating element. In this case, the intermediate element can also be understood as a transmission element.An intermediate element thus provides degrees of freedom for adjusting the movement of the brake element when actuated by means of the actuating element.

[0015] The intermediate element can comprise at least one slide that is movably mounted on the holding structure. The slide is driven by the actuating element. The slide, in turn, drives the brake element directly or indirectly. A slide is a structurally simple and reliable intermediate element, ensuring reliable drive of the brake element.

[0016] In one example, the slide is made of a plastic material. Therefore, electrical insulation of the second end of the actuator from the slide is unnecessary. Furthermore, such a slide is comparatively lightweight yet robust.

[0017] The carriage can be mounted on the support structure via a sliding guide, allowing translational movement. In other words, the carriage is guided translationally on the support structure. Since the support structure can be designed to be mechanically stable in this context, the carriage is also reliably and mechanically stable mounted. Such a configuration is therefore mechanically robust.

[0018] It is also possible for the carriage to be movably mounted on the support structure via at least one articulated arm. In this alternative, the carriage is also reliably and mechanically stable mounted. The articulated arm can be rigid in this context and coupled to both the support structure and the carriage via localized joints. Alternatively, the articulated arm can be designed as a solid-state articulated arm. In this example, the joints can also be considered delocalized, since certain sections of the articulated arm provide the function of the joints, rather than specific components or elements.

[0019] In another embodiment, the carriage is connected to the support structure via an elastic bearing element. When the carriage moves, the elastic bearing element is deformed elastically. In this alternative as well, the carriage is mounted simply and robustly to the support structure. An elastic bearing element also has the advantage that the carriage can be assigned a starting position in which the elastic bearing element is, for example, undeformed. The bearing element can be configured such that, in the absence of external forces, the carriage is returned to this starting position by means of the elastic bearing element.

[0020] In one example, the elastic bearing element is designed as a leaf spring element. In another example, the elastic bearing element is designed as a diaphragm spring. In yet another example, the elastic bearing element is designed as a coil spring element.

[0021] The at least one intermediate element can comprise a plunger or an actuating pin with an end facing the brake element. The brake-element-side end of the plunger or actuating pin rests against the brake element or can be brought into contact with it. In this example, the brake element is driven by a plunger or actuating pin. This is structurally simple and robust. In particular, the brake element can be reliably subjected to compressive forces by means of a plunger or actuating pin.

[0022] In one example, the plunger or actuating pin is made of a plastic material.

[0023] Preferably, the end of the plunger or actuating pin facing the brake element is decoupled from the brake element or can be decoupled from it. In this example, no tensile force can be exerted on the brake element by means of the plunger or actuating pin, at least in one operating situation, and preferably in all operating situations. Preferably, however, compressive forces can be transmitted to the brake element by means of the plunger or actuating pin. With such a configuration, the brake element can be reliably driven by a compressive force using the plunger or actuating pin. Furthermore, the decoupling or decoupling capability also allows independent movements of the plunger or actuating pin relative to the brake element and vice versa.This is particularly advantageous when the braking element is self-reinforcing, meaning it only needs to be brought into contact with the cutting element to be braked, and further movement of the braking element results from the contact between the braking element and the cutting element, thus eliminating the need for an actuating element. Put simply, in such a configuration, the braking element can be initiated by a pressure force. Afterward, the braking element and the plunger or actuating pin can move independently of each other. On the actuating element or the actuator to which the actuating element belongs, a pull-off mechanism or pull-off feature allows the actuator or actuating element to return to a starting position that corresponds to a release position of the braking element, while the braking element itself remains in the braking position.This ensures reliable protection of the actuator or actuating element against load peaks resulting from the engagement of the braking element. This results in high reliability and a long service life for the actuator and actuating element.

[0024] In one example, the brake-side end of the plunger or actuating pin can lie along a direction parallel to the actuating element, between the first and second ends of the actuating element. The brake-side end of the plunger or actuating pin thus lies next to the actuating element. This results in a compact emergency brake assembly, as the brake-side end of the plunger or actuating pin does not increase the size of the emergency brake assembly along a dimension corresponding to the direction of the actuating element. Put simply, the brake-side end of the plunger or actuating pin does not extend beyond the length of the actuating element.

[0025] According to one variant, the plunger or actuating pin has a central axis that runs parallel to the actuating element. In this context, the central axis of the actuating pin can also be referred to as the pin axis, and the central axis of the plunger as the plunger axis. This results in forces acting within the actuating element and forces acting within the plunger or actuating pin running parallel to each other. This is mechanically advantageous.

[0026] The central axis of the plunger or actuating pin can be spaced apart from the actuating element. The central axes are therefore preferably arranged parallel but offset. This results in a design that is advantageous in terms of forces and is also compact.

[0027] The plunger or actuating pin can be guided on the retaining structure. This provides reliable and robust guidance for the plunger or actuating pin. Specifically, this is a longitudinal guide, i.e., a guide along the central axis of the plunger or actuating pin. Simultaneously, the guide can be designed to prevent the plunger or actuating pin from tilting. Preferably, the actuating pin or plunger is guided close to its end facing the brake element, e.g., in the half of the plunger or actuating pin that faces the brake element. In this way, the guide on the retaining structure allows for a particularly precise position and / or movement of the end facing the brake element, enabling the brake element to be actuated with high precision.

[0028] In one example, the plunger or actuating pin is guided in a guide channel formed on the mounting structure. An alternative to the guide channel is a through hole or bore. Such a guide is particularly simple in terms of structure and manufacturing.

[0029] Advantageously, the end of the actuating pin or plunger facing the brake element is rounded. This allows for the reliable transmission of forces from the actuating pin or plunger to the brake element, even with tolerances in the relative positions between the actuating pin or plunger and the brake element. In particular, the rounded end prevents force peaks resulting from these tolerances. Overall, such an emergency brake assembly is therefore particularly robust.

[0030] In one example, the plunger or actuating pin has a circular cylindrical shape. Such actuating pins or plungers are particularly easy to manufacture.

[0031] The actuator end of the plunger or actuating pin can be coupled to the slide. In this example, a slide and a plunger or actuating pin are used as intermediate elements. For instance, the coupling between the slide and the actuating pin or plunger can be rigid, meaning it can transmit both compressive and tensile forces along a central axis of the plunger or actuating pin. Furthermore, such a rigid coupling can transmit lateral forces. Alternatively, the coupling can be designed to transmit only compressive forces. In all variations, a reliable coupling between the slide and the actuating pin or plunger is achieved, resulting in a reliable drive coupling between the actuating element and the brake element.

[0032] In one embodiment, the actuating element is guided by a guide element. This prevents the actuating element from bulging, at least locally. Thus, the actuating element is protected from unwanted damage.

[0033] For example, the guide element is designed as a section of the mounting structure, in particular as a section of the actuator housing and / or the brake caliper. This results in a compact design.

[0034] The emergency brake assembly can also include a spring element that directly or indirectly biases the actuating element in a direction corresponding to a tensile load on the actuating element. The actuating element is thus held under tensile tension by the spring element. Shortening of the actuating element can therefore be used directly and precisely to drive the brake element. In particular, unwanted play within the drive coupling between the actuating element and the brake element is prevented. Furthermore, such spring bias ensures that the actuating element reliably and precisely returns to an unactuated state after actuation. It is understood that if a slide, plunger, or actuating pin is provided, the spring element can be supported on the slide, plunger, or actuating pin.Alternatively or additionally, the spring element can be supported on the holding structure and / or on the guide element.

[0035] The spring element can circumferentially surround the plunger or actuating pin, at least partially. Alternatively or additionally, the spring element and the plunger or actuating pin can be arranged coaxially. This results in a compact design of the emergency brake assembly. Furthermore, tilting moments that can result from the spring action are reduced.

[0036] In one variant, the spring element surrounds the actuating element, at least partially. This also results in a compact design of the emergency brake assembly.

[0037] Furthermore, this method promotes a purely axial spring action of the actuating element.

[0038] In one example, the mounting structure is formed by an actuator housing and / or a brake caliper. The actuating element is therefore attached to the actuator housing and / or the brake caliper. Such a design is simple and can be implemented compactly.

[0039] In an example where the retaining structure is formed by the actuator housing rather than the brake caliper, the actuator, which comprises the actuator housing and the actuating element, can be detachably mounted to the brake caliper. A standard tool may be required for this. Consequently, the actuator can be detached from the brake caliper and replaced if necessary, for example, in the event of a defect. Such a configuration is therefore easy to repair.

[0040] Furthermore, a control unit for the actuating element can be integrated, at least partially, into the actuator housing. This also results in a space-saving design for the emergency brake assembly.

[0041] According to one embodiment, a first sleeve is provided at the first end of the actuating element, and the first end of the actuating element is attached to the mounting structure via the first sleeve. The actuating element can be easily and reliably attached to the mounting structure by means of the sleeve. Furthermore, the sleeve can, if required, comprise an electrically insulating material, so that the sleeve includes or is an electrical insulating element.

[0042] According to a further embodiment, a second sleeve is provided at the second end of the actuating element, and the second end of the actuating element is coupled to the brake element via this second sleeve. The actuating element can be easily and reliably attached to the brake element or an intermediate element by means of the sleeve. Furthermore, the sleeve can, if required, comprise an electrically insulating material, so that the sleeve includes or is itself an electrical insulating element.

[0043] The first sleeve and / or the second sleeve can be injection-molded onto the actuator. This allows for simple and cost-effective manufacturing and attachment of the sleeves to the actuator. Because of the injection molding, further assembly steps for attaching the first sleeve and / or the second sleeve are eliminated.

[0044] Preferably, the length of the actuating element is shorter than a dimension of the emergency brake assembly along a direction parallel to the length of the actuating element. Alternatively or additionally, a length of the actuating element lies entirely within a dimension of the emergency brake assembly measured parallel to the length of the actuating element. The length of the actuating element thus does not determine a maximum outer dimension of the emergency brake assembly. This allows for the creation of a comparatively compact emergency brake assembly using the actuating element.

[0045] The actuating element and / or a section of the retaining structure can mechanically shield a drive coupling section of the brake element. In this context, a drive coupling section refers to a section of the brake element to which the second end of the actuating element is attached or where an intermediate element, such as a plunger or actuating pin, contacts the brake element. Viewed from the outside, the drive coupling section is therefore located further inside the emergency brake assembly than the actuating element and / or the section of the retaining structure. This provides protection against access to the drive coupling section with a human hand and against the ingress of foreign objects.

[0046] In another example, at least one section of an actuator housing can mechanically shield the drive coupling section of the brake element. Viewed again from the outside, the drive coupling section is located further inside the emergency brake assembly than the actuator housing. This again provides protection against access to the drive coupling section with a human hand, as well as protection against the ingress of foreign objects.

[0047] Furthermore, the problem is solved by a method for operating an emergency brake assembly with a movable brake element for braking a cutting element of a motor-driven tool. The emergency brake assembly also includes a wire-shaped actuating element comprising a shape-memory alloy. The actuating element is coupled to the brake element via a drive mechanism. The method comprises: Setting the brake element in motion by means of the actuating element and subsequently lifting or ending a movement coupling between the actuating element and the brake element.

[0048] In particular, this method sets the braking element in motion in such a way that it contacts the cutting element to be braked. In this case, the braking element can exert the desired braking effect. Preferably, the braking element interacts with the cutting element in a self-reinforcing manner. This means that the braking effect established upon initial contact between the braking element and the cutting element, e.g., in the form of a braking torque, is further increased due to an interaction between the braking element and the cutting element. This is possible, for example, if the braking element is designed as a brake cam or a pivotally mounted pressure piece. With such a method, a comparatively compact and relatively low-power actuating element can suffice to reliably achieve a comparatively strong braking effect.Disengaging or ending the motion coupling prevents unwanted mechanical influences from the braking element from acting back into the actuating element.

[0049] The underlying idea of ​​the method according to the invention can be summarized, in simplified terms, as follows: the braking element is merely pushed or nudged in the direction of the cutting element by means of the actuating element, so that the braking element comes into contact with the cutting element. The actuating element is then decoupled from the braking element, allowing the braking element to continue moving independently of the actuating element towards a braking position. In a position where the cutting element is being braked by means of the braking element, or has already been braked to a standstill, any intermediate element that may be present, e.g., the plunger or actuating pin, is thus separated from the braking element, i.e., spaced apart.In a variant where the actuating element is directly attached to the brake element, decoupling is achieved by ensuring that the actuating element, in a position where the cutting element is being braked by the brake element or has already been braked to a standstill, assumes a state in which it can no longer influence the movement of the brake element, or only to a minimal extent. For example, the actuating element is in a slack position in this context. Furthermore, the fact that the actuating element is decoupled from the brake element means that the travel distance of the drive coupling section of the brake element—that is, the range of motion of the drive coupling section that it undergoes during actuation—can be greater than the travel distance of the actuating element. Thus, an actuating element with a comparatively small travel distance can be combined with a brake element that has a comparatively large travel distance.

[0050] It is understood that the method according to the invention can be carried out using the emergency brake assembly according to the invention.

[0051] According to one variant, the method further includes resetting the actuating element to its initial position, whereby the resetting occurs independently of the braking element. The actuating element can thus be reset while the braking element is still in a braking position. The braking element can then be reset subsequently. In this way, the actuating element is made ready for use again as soon as possible after being actuated.

[0052] The problem is further solved by a method for operating an actuator of an emergency braking unit for a motor-driven tool. The actuator has an actuating element comprising a shape-memory alloy. The actuating element is coupled to at least one electrical energy storage unit via an electrical switching element, such that the actuating element can be selectively supplied with electrical energy stored in the energy storage unit by actuating the switching element. The method comprises: Acquiring or receiving an environmental parameter and / or a first operating parameter of the actuator and / or a second operating parameter of the tool equipped with the actuator, and operating the actuator depending on the acquired or received environmental parameter and / or the acquired or received first operating parameter and / or the acquired or received second operating parameter.

[0053] In this context, the terms "first operating parameter" and "second operating parameter" are used solely to better distinguish between an operating parameter of the actuator and an operating parameter of the tool equipped with the actuator. A number of operating parameters is not implied. The method according to the invention thus takes into account an environmental parameter that describes the environment in which the actuator of the emergency braking unit is operated, and / or a first operating parameter that characterizes an operating state of the actuator, and / or a second operating parameter that characterizes an operating state of the tool equipped with the actuator.By operating the actuator based on environmental parameters and / or the first and / or second operating parameters, it is ensured that the actuator always operates with consistent characteristics, even if these parameters vary. The actuator therefore functions reliably regardless of the environmental parameters and / or the first and / or second operating parameters. This also applies, of course, to multiple actuations of the actuator. It goes without saying that the actuator can only be operated based on a parameter that has been previously detected or maintained. Specifically, this ensures that the actuating element receives a current with each actuation that is sufficiently high to guarantee safe and reliable actuator operation.In particular, sufficiently fast actuator actuation is achieved. At the same time, the current can be selected to be so low that excessive aging or even damage to the actuator is avoided. A low current implies a low thermal stress on the shape memory alloy. This leads to relatively slow aging. Consequently, an actuator operated using the method according to the invention exhibits high reliability and a long service life.

[0054] The tool can be a hand-held tool, which can also be called a hand tool, a semi-stationary tool, or a stationary tool.

[0055] In a preferred embodiment, the tool is a saw. This can be a handsaw, a semi-stationary saw, or a stationary saw. An example of a handsaw is a handheld circular saw. An example of a semi-stationary saw is a portable table saw. An example of a stationary saw is a panel saw.

[0056] The electrical energy storage unit can be an electrical capacitor or a battery. It is irrelevant whether the electrical energy storage unit, i.e., the capacitor or the battery, is structurally integrated as a component of the actuator or as a component of the tool. The only requirement is that the electrical energy storage unit is electrically coupled to the actuating element.

[0057] The emergency braking unit is, in particular, a multi-triggerable emergency braking unit.

[0058] The ambient parameter can include a measured or maintained ambient temperature. This allows the actuator to be operated with high reliability regardless of the ambient temperature. At the same time, undesirable aging effects can be avoided. This is because, depending on the ambient temperature, a current can be selected to actuate the actuator that is sufficient for reliable operation without causing unnecessary thermal stress. Specifically, a relatively low current is selected at a comparatively high ambient temperature, and a comparatively high current is selected at a comparatively low ambient temperature.

[0059] The first operating parameter can include the temperature of the actuator. As mentioned earlier, the actuator's function relies on a thermally activated lattice transformation of the shape memory alloy. This ensures reliable operation of the actuator while simultaneously preventing excessive thermal stress, which can lead to undesirable aging effects of the shape memory alloy.

[0060] Alternatively or additionally, the second operating parameter can include the tool's rotational speed and / or power consumption. Therefore, triggering the emergency braking system via the actuator is only permissible if the second operating parameter exceeds a defined rotational speed and / or power consumption.

[0061] According to one embodiment, operating the actuator depending on the detected or obtained environmental parameter and / or the detected or obtained first operating parameter and / or the detected or obtained second operating parameter comprises setting an actuation current parameter for the actuating element depending on the detected or obtained environmental parameter and / or the detected or obtained first operating parameter and / or the detected or obtained second operating parameter. Again, it is understood that the actuator can only be operated depending on a parameter that has previously been detected or obtained. In this context, the actuation current parameter is understood as a characteristic value that describes the current used to actuate the actuating element. The actuation current parameter describes, for example, a maximum actuation current or a duration of current application.It is emphasized that, due to the comparatively short actuation time of only a few milliseconds, the actuation current parameter is set before actuation. The actuation current parameter has a direct influence on the aging of the actuating element.

[0062] In one variant, the actuation current parameter is set by adjusting an electrical resistance acting between the energy storage unit and the actuating element, depending on the detected or obtained environmental parameter and / or the detected or obtained first operating parameter and / or the detected or obtained second operating parameter. The electrical resistance is used to adjust the current profile acting on the actuating element.

[0063] In another variant, the actuation current parameter is set by adjusting the capacity of the energy storage unit depending on the detected or received environmental parameter and / or the detected or received first operating parameter and / or the detected or received second operating parameter. This determines the amount of charge that can be stored in the energy storage unit and introduced into the actuation element via the switching element. It is understood that a comparatively large amount of charge results in a comparatively high and / or a comparatively long-lasting actuation current.

[0064] In this context, an energy storage unit with adjustable capacity can be created by selecting an energy storage unit whose capacity is inherently adjustable. Alternatively, an energy storage unit can be selected that comprises two or more energy storage elements, each of which can be selectively switched on and off.

[0065] It is also possible to adjust the actuation current parameter by setting a storage voltage of the energy storage unit as a function of the detected or received environmental parameter and / or the detected or received first operating parameter and / or the detected or received second operating parameter. The storage voltage also determines the amount of charge that can be stored in the energy storage unit and introduced into the actuation element via the switching element. It is understood that a comparatively large amount of charge results in a comparatively high and / or a comparatively long-lasting actuation current.

[0066] Alternatively or additionally, the actuation current parameter can be set by defining an actuation time of the switching element depending on the detected or received environmental parameter and / or the detected or received first operating parameter and / or the detected or received second operating parameter. Thus, the duration of the current application is set depending on the environmental parameter and / or the first operating parameter and / or the second operating parameter.

[0067] According to one embodiment, the actuator is temperature-controlled. This means that the temperature of the actuator is set to a specific value or a specific range. If the temperature control raises the actuator to a temperature above the ambient temperature, this can also be referred to as preheating. Alternatively, this can be called priming. Temperature-controlled actuators allow them to be actuated regardless of the ambient temperature. In particular, a constant energy is required for actuation, irrespective of the ambient temperature. In other words, a first operating parameter of the actuator, which describes its temperature, is kept constant or within a predetermined range.This ensures that the actuating element functions reliably on the one hand and that aging processes are prevented on the other.

[0068] The actuator can be temperature-controlled in two ways. Either heat is applied to the actuator from the outside, or an electric current is passed through it, causing it to heat up. In both cases, the temperature of the actuator can be precisely set. Naturally, these temperature control methods can also be combined.

[0069] The actuator can be tempered to a temperature above the ambient temperature and below its switching temperature, i.e., the temperature at which grid transformation begins. For example, the actuator is tempered to a temperature that corresponds to 50% to 90% of its switching temperature. This allows the actuator to be operated from the tempered state using a comparatively small actuation current and / or charge quantity. Since a minimum temperature of the FGL wire is ensured through tempering, an actuation current can be selected that is lower than the current required at a lower actuator temperature.This also helps to protect the actuator from unwanted aging effects caused by excessively high currents and / or to ensure maximum performance over time, regardless of the ambient temperature.

[0070] In this context, it is possible, on the one hand, to temper the actuator to a specific temperature. On the other hand, a temperature-resistance characteristic of the shape memory alloy can be used to temper the actuator to a temperature corresponding to its maximum electrical resistance. The first case is referred to as temperature-dependent preheating or tempering. The second case is referred to as resistance-dependent preheating or tempering.

[0071] In one variant, the tool is deactivated until a desired minimum temperature of the actuating element is reached. This ensures that the emergency braking unit is ready for use before the tool can be used.

[0072] Alternatively, the tool can be used to issue a warning signal or message as long as a desired minimum temperature of the actuator has not yet been reached. This allows the user to decide, knowing whether or not to use the tool, whether or not the emergency brake unit is ready for operation.

[0073] In another alternative, if the desired minimum temperature of the actuating element has not yet been reached, a sufficiently large actuating current and / or a sufficiently large actuating charge quantity is set. As soon as the desired minimum temperature is reached, the actuating current and / or the actuating charge quantity is reduced.

[0074] The problem is further solved by means of a control circuit for an actuator of an emergency braking unit for a motor-driven tool. The actuator has an actuating element which comprises a shape-memory alloy. The control circuit comprises at least one electrical energy storage unit and one electrical switching element. The electrical energy storage unit and the electrical switching element can be electrically coupled to the actuating element, so that the actuating element can be selectively supplied with electrical energy stored in the energy storage unit by actuating the switching element.The energy storage unit has an adjustable capacity, and / or the control circuit includes an adjustable resistor, and / or the control circuit includes an adjustable voltage converter electrically coupled to the energy storage unit, allowing for an adjustable storage voltage of the energy storage unit, and / or the electrical switching element has an adjustable actuation time. All of these options can be used to set an actuation current parameter. This can be done depending on the ambient parameter, the first operating parameter, and / or the second operating parameter. As mentioned earlier, the actuation current parameter describes, for example, a maximum actuation current or a duration of current application.Using such a control circuit, an actuating element comprising a shape memory alloy can be controlled in a way that, on the one hand, ensures fast and reliable actuation and, on the other hand, prevents undesirable aging effects.

[0075] The adjustable voltage converter is, for example, a so-called boost converter.

[0076] The control circuit can further include a temperature control device which can be coupled to the actuator for temperature control purposes. Such a temperature control device allows the effects and advantages already mentioned in connection with the temperature control process step to be achieved. Reference is made to the above explanations.

[0077] The temperature control device can include a measuring device for measuring the temperature of the actuator and / or its electrical resistance. The electrical resistance can be measured by a combined measurement of the current flowing through the actuator and the voltage drop across it. This allows the actuator to be temperature-controlled via a closed-loop system, enabling particularly precise temperature control.

[0078] In a case where a temperature-resistance characteristic of the actuating element is known, a temperature and a resistance can be converted into each other.

[0079] The problem is further solved by an actuator unit comprising a control circuit according to the invention and an actuator. The actuator has an actuating element which includes a shape memory alloy. The actuator is electrically coupled to the control circuit. The actuating element can thus be selectively supplied with a current that is sufficiently large to ensure safe and reliable actuation of the actuator. In particular, sufficiently fast actuation of the actuator is achieved. At the same time, however, the current is so small that excessive aging or even damage to the actuator is avoided. A low current implies a low thermal stress on the shape memory alloy. This leads to relatively slow aging. Consequently, such an actuator unit exhibits high reliability and a long service life. In particular, the actuator unit can be actuated multiple times.

[0080] Preferably, the actuating element has the form of a wire. Because the actuating element comprises a shape-memory alloy, this wire shortens when heated to a temperature above a trigger threshold. Such a trigger threshold can also be referred to as the switching temperature. When the wire cools back down to its ambient temperature, the shortening is reversed.

[0081] According to one variant, the actuating element is thermally insulated from its environment. Since the actuating element encloses the shape memory alloy, the shape memory alloy is also thermally insulated from its environment. This dampens temperature fluctuations in the shape memory alloy, thus slowing down undesirable aging of the alloy.

[0082] The problem is also solved by an emergency braking unit for a motor-driven tool with an actuator unit according to the invention. Such an emergency braking unit has high reliability and a long service life. In particular, the emergency braking unit can be used multiple times, with reliability remaining at a high level throughout its entire service life.

[0083] Furthermore, the effects and advantages mentioned for one of the inventive method, inventive control circuit, inventive actuator unit and inventive emergency brake unit also apply in the same way to all others of the inventive method, inventive control circuit, inventive actuator unit and inventive emergency brake unit.

[0084] The invention is explained below with reference to various embodiments shown in the accompanying drawings. These show: Figure 1 shows a sawing device with an emergency braking unit, which is equipped with an actuator unit comprising a control circuit according to the invention and an actuator that can be operated by a method; Figure 2 shows the sawing device made of Figure 1 , wherein a housing part and a protective cover are omitted, Figure 3 shows a section through the saw device Figure 2 along plane III, figure 4 in one of the Figure 3 In the corresponding view, an alternative embodiment of the emergency braking unit is shown in Figure 5 in a view along direction V. Figure 2 the emergency brake unit in an isolated representation, Figure 6 in a Figure 3 In a corresponding view, another alternative embodiment of the emergency braking unit is shown in Figure 7. Figure 3In the corresponding view, another alternative embodiment of the emergency brake unit is shown, Figure 8 shows a view of an emergency brake unit according to another embodiment, Figure 9 shows a section through the emergency brake unit made of Figure 8 along plane IX-IX, Figure 10, the actuator unit according to the invention from the Figures 1 and 2 in the form of an electrical circuit diagram, wherein the actuator is represented by the actuating element in the form of a wire made of a shape memory alloy, Figure 11 an alternative embodiment of the actuator unit according to the invention in one of the Figure 6 corresponding illustration, Figure 12 shows a further alternative embodiment of the actuator unit according to the invention in a representation as in the Figures 6 and 7 , and Figure 13 shows another alternative embodiment of the actuator unit according to the invention in a representation as shown in the Figures 6 to 8 .

[0085] The Figures 1 and 2Figure 1 shows a motor-driven tool 8, which in the example shown is a sawing device 10, more precisely a miter saw.

[0086] The sawing device 10 comprises a base part 12, which has a support surface 14 for a workpiece 16. The workpiece 16 is to be understood as exemplary.

[0087] Furthermore, the sawing device 10 has a swiveling device 18 which is pivotally mounted on a first section 18a on the base part 12. A disc-shaped saw blade 20 is mounted on a second section 18b, which is spaced apart from the first section 18a. A handle 22 is also provided on the second section 18b.

[0088] A user of the saw device 10 can thus use the handle 22 to bring the saw blade 20 into a rotating state in interaction with the workpiece 16 supported on the support surface 14, so that it is sawn or cut off.

[0089] The sawing device 10, i.e. the motor-driven tool 8, is further equipped with an emergency braking unit 24.

[0090] The emergency braking unit 24 is designed to brake the saw blade 20 to a standstill if, in a state in which the saw blade 20 is rotating, it is detected that a user is coming into contact with the saw blade 20 or that such contact is imminent.

[0091] In this context, the saw blade 20 is used as a capacitive sensor element; that is, its electrical capacitance is continuously measured. If the electrical capacitance is outside a predefined normal range, a contact is detected.

[0092] In the Figures 3 to 9 Various versions of the emergency braking unit 24 can be seen.

[0093] In this context, the emergency brake unit 24 has a brake caliper 26 which overlaps an edge of the saw blade 20, so that a pressure element 28 provided on the brake caliper 26 is arranged on a first axial side of the saw blade 20 and a brake cam 30 rotatably mounted on the brake caliper 26 is arranged on a second axial side of the saw blade 20.

[0094] In a more general form, the brake cam 30 can also be referred to as brake element 29.

[0095] The brake cam 30 is coupled to an actuator unit 32, which includes an actuator 31 and a control circuit (to be explained later) that is electrically coupled to the actuator. By means of the actuator 31, the brake cam 30 can be selectively rotated such that it presses the saw blade 20 against the pressure element 28 and consequently brakes it to a standstill.

[0096] In the variant from Figure 3The actuator 31 comprises an actuating element 34, which includes a shape memory alloy 36. Specifically, the actuating element 34 is designed as a wire made of the shape memory alloy 36.

[0097] The actuating element 34 is attached at a first end 34a to a mounting element receptacle. The mounting element receptacle can be part of the brake caliper 26 or part of a retaining structure 35 fixed to the brake caliper 26. The retaining structure 35 can be formed by an actuator housing 39 that is attached to the brake caliper 26.

[0098] Of course, the retaining structure 35 can also be formed by the brake caliper 26 or by the brake caliper 26 and the actuator housing 39 together.

[0099] The other end 34b of the actuating element 34 is attached to a slide 38, which is mounted so as to be translationally displaceable relative to the brake caliper 26. The slide 38 is spring-loaded in a direction corresponding to a tensile load on the actuating element 34. Furthermore, the slide 38 is coupled or can be coupled to the brake cam 30 via an actuating pin 40.

[0100] When the actuating element 34 is subjected to a sufficiently large electric current, a thermally induced lattice transformation of the shape memory alloy 36 takes place, causing the actuating element 34 to shorten. This results in a displacement of the slide 38 and the actuating pin 40 to the right. Figure 3 As a result, the brake cam 30 engages with the saw blade 20 and brakes it until it comes to a standstill.

[0101] For better understanding, the following are included: Figure 3The actuating pin 40 and the brake cam 30 are shown with solid lines in an unactuated state. The unactuated state refers to a state in which the actuating element 34 has not yet been supplied with a sufficiently large electric current. Accordingly, the brake cam 30 does not interact with the saw blade 20. Furthermore, the actuating pin 40 and the brake cam 30 are shown with dashed lines in an actuated state. In this state, the actuating element 34 has been supplied with a sufficiently large electric current, such that... Figure 3 The actuating pin 40 has shifted to the right and the brake cam 30 has rotated clockwise. The saw blade 20 is thus clamped between the brake cam 30 and the pressure element 28. In the actuated state, the actuating pin 40 and the brake cam 30 are separated from each other, i.e., spaced apart.

[0102] The Figure 4Figure 1 shows an alternative embodiment of the actuator unit 32. In this embodiment, the first end 34a of the actuating element 34 is fixed relative to the brake caliper 26 as before.

[0103] Unlike the variant made of Figure 3 The second end 34b is attached to the brake cam 30. The brake cam 30 is spring-loaded. The direction of the load again corresponds to a tensile load direction for the actuating element 34.

[0104] Will the variant be made up of Figure 4 When the actuating element 34 is subjected to a sufficiently large electric current, a thermally induced lattice transformation of the shape memory alloy 36 takes place, causing the actuating element 34 to shorten. This results in a rotation of the brake cam 30, which engages with the saw blade 20 and brakes it to a standstill. In the Figure 4The brake cam 30 rotates clockwise when the emergency brake unit 24 is triggered.

[0105] The actuator 31 for operating the emergency brake unit 24 thus has the actuating element 34, which comprises a shape memory alloy 36, the retaining structure 35 and a spring element 37 arranged on the retaining structure 35, wherein the spring element 37 biases the second end 34b of the actuating element 34 relative to the first end 34a of the actuating element 34 and / or defines a preferred position of the actuating pin 40, which preferably extends along a pin axis 40a, relative to the retaining structure 35.

[0106] The actuating element 34 always extends along a shortening direction that runs from the first end 34a of the actuating element 34 to the second end 34b of the actuating element 34.

[0107] In the Figure 3In the variant shown, the actuating pin 40 is mounted so that it can be displaced translationally relative to the holding structure along the pin axis 40a. The actuating pin 40 is mounted in a through-hole of the holding structure 35.

[0108] The actuating element 34 is attached with its first end 34a to the fastening element receptacle of the holding structure 35 and with its second end 34b is coupled or can be coupled to the brake cam 30.

[0109] In the Figure 3 In the variant shown, the second end 34b is coupled or can be coupled to the brake cam 30 via the actuating pin 40.

[0110] Preferably, the pin axis 40a and the shortening direction of the actuating element 34 run parallel.

[0111] Alternatively or additionally, the actuating pin 40 and the second end 34b of the actuating element 34 can be moved parallel to each other in the same direction by triggering the emergency brake unit 24.

[0112] Preferably, this is a linear movement.

[0113] In the Figure 3 In the variant shown, the actuating pin 40 and the second end 34b of the actuating element 34 are coupled by means of the slide 38, so that the actuating pin 40 can be brought into engagement with the brake cam 30 via the slide 38.

[0114] The slide 38 engages with a guide contour arranged on the holding structure 35. This prevents the slide 38 from rotating relative to the holding structure. Alternatively, the actuating pin 40 can also engage with a guide contour arranged on the holding structure.

[0115] In the Figure 4 In the variant shown, the second end 34b of the actuating element 34 engages directly with the brake cam 30.

[0116] The first end 34a and the second end 34b of the actuating element 34 are, for example, received in sleeves 84a, 84b. The sleeves 84a, 84b can be pressed or crimped onto the actuating element 34, i.e., onto the wire made of the shape-memory alloy 36. Thus, the wire can be easily coupled at its first end 34a to the retaining structure and at its second end 34b to the slide 38 or the brake cam 30.

[0117] Alternatively, it is also conceivable that the first end 34a and the second end 34b of the actuating element 34 are overmolded, for example, with an electrically insulating plastic, to form a sleeve 84a, 84b. In other words, according to this alternative, the sleeves 84a, 84b are injection-molded onto their respective first end 34a or second end 34b.

[0118] However, it is also conceivable that the second end 34b is overmolded with and / or embedded in the slide 38.

[0119] Alternatively or additionally, the first end 36a can be overmolded and / or embedded in the holding structure.

[0120] The first end 34a and the second end 34b of the actuating element 34 preferably form the electrical connections of the actuating element 34. For example, cables are soldered, crimped or plugged in directly to the first end 34a and the second end 34b.

[0121] In the variant from Figure 6 The actuator 31 also includes an actuating element 34, which comprises a shape memory alloy 36. Specifically, the actuating element 34 is, as before, designed as a wire made of the shape memory alloy 36.

[0122] The actuating element 34 is attached with a first end 34a to a fastening element receptacle of the holding structure 35, which in the illustrated example is formed by the actuator housing 39.

[0123] The other end 34b of the actuating element 34 is attached to a slide 38, which is movably mounted on the holding structure 35, i.e. on the actuator housing 39, via two elastic bearing elements 74, which in this case are each designed as leaf spring elements.

[0124] As already explained, both ends 34a, 34b of the actuating element 34 are provided with molded sleeves 84a, 84b.

[0125] In this context, the slide 38 is essentially L-shaped, with the relatively longer leg of the L-shaped slide 38 being aligned parallel to the actuating element 34.

[0126] The two elastic bearing elements 74 are connected to the relatively longer leg.

[0127] The relatively shorter leg of the L-shaped slide 38 is essentially aligned at right angles to the relatively longer leg.

[0128] An actuating pin 40 with a pin axis 40a, more precisely an actuating element-side end of the actuating pin 40, is rigidly connected to the relatively shorter leg. The actuating pin 40 points away from the relatively longer leg and extends through a through-opening provided in the retaining structure 35, i.e., the actuator housing 39, such that a free end of the actuating pin 40 lies adjacent to the brake element 29, which in this case has the form of a brake cam 30. The brake element-side end 41 of the actuating pin 40 can thus bear against the brake element 29, i.e., the brake cam 30, or, when the actuating element 34 is actuated, be pressed against the brake element 29, i.e., the brake cam 30.

[0129] There is no tensile coupling between the actuating pin 40 and the brake element 29, i.e., the brake cam 30. This means that no tensile forces can be introduced into the brake element 29 by means of the actuating pin. This also applies to the embodiment shown in Figure 3 .

[0130] The free end of the actuating pin 40, i.e. the brake element-side end 41 of the actuating pin 40, is rounded.

[0131] The through-opening, through which the actuating pin 40 extends, serves to guide the actuating pin 40.

[0132] Furthermore, a stop ring is attached in the area of ​​the brake element-side end 41 of the actuating pin 40, by means of which a movement of the brake element-side end 41 of the actuating pin 40 in the direction of the retaining structure 35, i.e. in the direction of the actuator housing 39, is limited.

[0133] A central axis of the actuating pin 40, i.e. a pin axis 40a, runs parallel-offset to the actuating element 34.

[0134] When the actuating element 34 is subjected to a sufficiently large electric current, a thermally induced lattice transformation of the shape memory alloy 36 takes place, causing the actuating element 34 to shorten. This results in a displacement of the slide 38 and the actuating pin 40 to the right. Figure 6 As a result, the brake cam 30 engages with the saw blade 20 and brakes it until it comes to a standstill.

[0135] This movement of the slide 38 is limited by a possible contact of the relatively shorter leg of the slide 38 with the holding structure 35, i.e., with the actuator housing 39.

[0136] If the actuating element 34 is no longer supplied with current and cools down accordingly, the previously thermally induced lattice transformation reverses and the actuating element 34 elongates again to its original length.

[0137] The slide 38 is always spring-loaded in a direction corresponding to a tensile load on the actuating element 34 by means of the elastic bearing elements 74. In this way, the slide 38 is reliably returned to its starting position.

[0138] In summary, the embodiment according to Figure 6 the second end 34b of the actuating element 34 is coupled via the slide 38 and the actuating pin 40 to the brake element 29, i.e. the brake cam 30.

[0139] For the sake of a compact design, the brake-element-side end 41 of the actuating pin 40 is arranged along a direction parallel to the actuating element 34 between the first end 34a and the second end 34b of the actuating element 34. This is evident from the view of the Figure 6 This becomes immediately clear if one mentally draws a perpendicular line to the actuating element 34 at each end 34a, 34b, intersecting the pin axis 40a. The brake-element-side end 41 of the actuating pin 40 then lies between these two points of intersection.

[0140] Furthermore, a length L BE of the actuating element 34 in the embodiment according to Figure 6smaller than a dimension A of the emergency brake unit 24 along a direction parallel to the length L BE of the actuating element 34. Furthermore, the length L BE of the actuating element lies completely within a dimension A of the emergency brake unit 24 measured parallel to the length L BE of the actuating element 34. The dimension A, which can also be referred to as the maximum dimension, is formed by a dimension of the brake caliper 26 measured parallel to the actuating element. It is based on the Figure 6 It is immediately apparent that the actuating element 34 is shorter than this dimension A. If measurements are taken at the beginning and end of dimension A of the brake caliper 26 in the Figure 6 If vertical lines running from top to bottom are drawn, the actuating element 34 lies between these lines.

[0141] Figure 7 shows another embodiment, which is the embodiment from Figure 6similarities. Therefore, only the differences compared to the embodiment from will be discussed below. Figure 6 explained. Furthermore, reference can be made to the explanations regarding the embodiment according to Figure 6 be referred.

[0142] A first difference in the embodiment according to Figure 7 and the embodiment according to Figure 6 The feature is that the slide 38 is mounted on the holding structure 35, i.e. on the actuator housing 39, in a manner that allows movement by means of two articulated arms 76.

[0143] The articulated arms 76 are rigid in themselves. However, they are connected to the slide 38 via a first pivot joint and to the holding structure 35 via a second pivot joint.

[0144] A second difference is that a spring element 37 is now provided again. The spring element 37 is arranged between the relatively shorter leg of the L-shaped slide 38 and a section of the holding structure 35, i.e., the actuator housing 39, opposite this leg.

[0145] The slide 38 is therefore always spring-loaded in a direction by the spring element 37 that corresponds to a tensile load on the actuating element 34. In this way, the slide 38 is reliably returned to its starting position when the actuating element 34 is no longer energized.

[0146] Furthermore, the spring element 37, which is designed as a spiral spring, surrounds the actuating pin 40 circumferentially.

[0147] The spring element 37 and the actuating pin 40 are also arranged coaxially.

[0148] Another embodiment of an emergency braking unit 24 is described in the Figures 8 and 9 shown. This shows the Figure 8 among other things, a brake caliper 26 of the emergency brake unit 24 is shown in a view along a direction that lies within a saw blade plane of the saw blade 20. The position of the saw blade 20 is indicated by dashed lines.

[0149] Figure 9 shows a corresponding section view in a plane IX-IX.

[0150] In the embodiment according to Figures 8 and 9 The actuating element 34 and a slide 38, to which the second end 34b of the actuating element 34 is attached, are arranged on a common carrier plate 78, which is designed, for example, as a circuit board.

[0151] The carrier plate 78 also includes a control circuit 42, which will be explained in detail below. The carrier plate 78 with the control circuit 42 can be referred to as the control unit.

[0152] As before, the brake cam 30 can be actuated by means of an actuating pin 40 rigidly attached to the slide 38.

[0153] The carrier plate 78 and the actuating element 34 are positioned such that they mechanically shield a drive coupling section of the brake element 29, i.e., a region of the brake cam 30 designed for the engagement of the actuating pin 40. This is particularly evident from the view in Figure 9 clearly.

[0154] In this view, a human finger or hand cannot reach the drive coupling section from above, as access is blocked by the carrier plate 78 and the actuating element 34. The same applies to foreign objects, e.g., dirt particles.

[0155] As already mentioned in connection with the embodiment from Figure 6 explained, is also in the embodiment according to Figures 8 and 9The length L BE of the actuating element 34 is smaller than a dimension A of the emergency brake unit 24 along a direction parallel to the length L BE of the actuating element 34. Furthermore, the length L BE of the actuating element 34 lies entirely within a dimension A of the emergency brake unit 24 measured parallel to the length L BE of the actuating element 34.

[0156] In all previously explained variants, the slide 38 and the actuating pin 40 can be more generally referred to as intermediate elements 80.

[0157] Another term for the actuating pin 40 is plunger.

[0158] Furthermore, in the examples described above, a combination of actuator 31 and brake element 29, i.e., brake cam 30, can be referred to as the emergency brake assembly 82. The emergency brake assembly 82 thus represents a subunit of the emergency brake unit 24, the emergency brake unit 24 being, as already explained, designed to brake the saw blade 20 to a standstill.

[0159] The Figure 10 Figure 3 shows an embodiment of the actuator unit 32 in the form of an electrical circuit diagram.

[0160] The actuating element 34 of the actuator 31 is represented by a variable resistance R BE.

[0161] The actuator 31, i.e. the actuating element 34, is electrically connected to a control circuit 42 which is designed to selectively apply electrical energy to the actuating element 34, so that the aforementioned structural transformation is induced.

[0162] For this purpose, the control circuit 42 includes an electrical energy storage unit 44 in the form of a capacitor with adjustable capacitance.

[0163] Furthermore, the control circuit 42 includes an electrical switching element 45 by means of which the energy storage unit 44 and the actuating element 34 can be selectively electrically coupled. The electrical coupling is effected via an optional resistor 46.

[0164] The control circuit 42 also includes a charging circuit 48 for the energy storage unit 44. This unit has a DC voltage source 50, which is coupled to the energy storage unit 44 via an adjustable voltage converter 52 and another electrical switching element 54. The electrical resistance of the charging circuit 48 is specified by the resistance RLS.

[0165] Both the electrical switching element 45 and the other electrical switching element 54 are actuated by means of a trigger control unit 56, which is coupled to the saw blade 20 acting as a sensor element.

[0166] In an initial state, the electrical switching element 45 is open, meaning that the actuating element 34 is electrically disconnected from the energy storage unit 44. The other switching element 54 is closed, so that the energy storage unit 44 is brought to or maintained at a desired state of charge by means of the DC voltage source 50.

[0167] When the trigger control unit 56 detects actual or imminent contact between the user and the saw blade 20, the electrical switching element 45 is closed and the other electrical switching element 54 is opened. This electrically connects the energy storage unit 44 to the actuating element 34, causing an electric current to flow through the actuating element 34, which induces a structural transformation of the shape memory alloy 36.

[0168] In the embodiment from Figure 10This can be done depending on a first operating parameter B1 of the actuator 31. In the illustrated embodiment, this parameter is either an electrical resistance or a temperature. Since the actuating element 34 has a characteristic, temperature-dependent electrical resistance, the electrical resistance and the temperature are interconvertible. The behavior of the electrical resistance of the actuating element 34 as a function of temperature can be assumed to be known.

[0169] For this purpose, the control circuit 42 includes a current measuring unit 58, which measures a current I BE flowing through the actuating element 34, and a voltage measuring unit 60, which measures a voltage drop U BE across the actuating element.

[0170] Both the current measuring unit 58 and the voltage measuring unit 60 are signal-linked to a state control unit 62. Using the state control unit 62, the electrical resistance of the actuating element 34 can be calculated based on the voltage UBE and the current IBE. Furthermore, the temperature of the actuating element 34 can be determined using the known relationship between electrical resistance and temperature.

[0171] The state control unit 62 is also coupled to the voltage converter 52 via a signal connection. This makes it possible to set a voltage, depending on the resistance or temperature of the actuating element 34, which is then distributed between the adjustable resistor 46 and the energy storage unit 44. In other words, a storage voltage for the energy storage unit 44 can be set.

[0172] It is understood that current must flow through the actuating element 34 in order for its electrical resistance and / or temperature to be determined by the current measuring unit 58 and the voltage measuring unit 60. This means that the resistance and / or temperature can be measured during actuation of the actuating element 34.

[0173] Alternatively or additionally, a measurement procedure can be carried out using the trigger control unit 56, in which the actuating element 34 is only temporarily energized to measure the resistance and / or the temperature.

[0174] The state control unit 62 is also signal-linked to an environmental sensor 63a, which can detect an environmental parameter U. In the example shown, the environmental parameter U is the ambient temperature. The voltage converter 52 and / or the energy storage unit 44 can therefore also be operated and / or adjusted depending on the ambient temperature.

[0175] Additionally, the state control unit 62 is signal-linked to a tool state sensor 63b. This sensor is designed to determine a second operating parameter B2 of the tool 8 equipped with the actuator 31. In this example, this parameter is a speed sensor that measures the rotational speed of the tool 8. The voltage converter 52 and / or the energy storage unit 44 can therefore also be operated and / or adjusted depending on the rotational speed.

[0176] Figure 11An alternative embodiment of the actuator unit 32 is shown in the form of an electrical circuit diagram. The following discussion focuses solely on the differences from the embodiment according to... Figure 10 Received. Identical or corresponding elements are given the same reference symbols.

[0177] First, in the embodiment according to Figure 11 The energy storage unit 44 is no longer adjustable, but has a constant storage capacity.

[0178] The electrical resistance 46 is again optional.

[0179] In addition, a heating circuit or temperature control device 64 is now provided.

[0180] In this context, the electrical switching element 45 is modified such that, in a first position, it electrically connects the energy storage unit 44 to the actuating element 34 as before.

[0181] In a second position, the electrical switching element 45 connects the actuating element 34 to the heating circuit or temperature control device 64, so that a heating current can be passed through the actuating element 34 to heat it to a desired temperature.

[0182] In the embodiment according to Figure 11 The state control unit 62 also includes a heating controller 66.

[0183] The heating controller 66 uses the current I BE determined by means of the current measuring unit 58 and the voltage U BE determined by means of the voltage measuring unit 60 as input parameters.

[0184] The current measuring unit 58 and the voltage measuring unit 60 thus form a measuring device of the temperature control device 64, by means of which a temperature of the actuating element 34 and / or an electrical resistance of the actuating element 34 can be measured.

[0185] As already mentioned, an electrical resistance of the actuating element 34 can be calculated from this, or, using the known relationship between temperature and electrical resistance, a temperature of the actuating element 34.

[0186] Thus, the heating controller 66 can be operated with a temperature as the control variable or with an electrical resistance as the control variable.

[0187] For this purpose, an additional electrical switching element 68 is controlled by means of the heating controller 66, e.g. with a pulse width modulated signal.

[0188] The voltage converter 52 is set as before.

[0189] Figure 12 Figure 3 shows another, alternative embodiment of the actuator unit 32 in the form of an electrical circuit diagram. The following discussion focuses solely on the differences compared to the embodiments according to Figure 3. Figure 10 and Figure 11Received. Identical or corresponding elements are given the same reference symbols.

[0190] In contrast to the embodiment according to Figure 11 is in the embodiment according to Figure 12 The voltage converter 52 is no longer adjustable. This means that the voltage converter 52 always sets the voltage of the energy storage unit 44, which in this case is formed by the energy storage elements 44a, 44b, to a fixed value.

[0191] The energy storage unit 44 now comprises two energy storage elements 44a, 44b, each designed as an electrical capacitor.

[0192] These are electrically connected in parallel.

[0193] Furthermore, instead of just one optional electrical resistor 46, two optional electrical resistors 46a, 46b are now provided, each connected in parallel to each other and in series with one of the energy storage elements 44a, 44b.

[0194] The energy storage element 44a and the electrical resistor 46a can be coupled to the DC voltage source 50 via the electrical switching element 54 as before.

[0195] The energy storage element 44b and the electrical resistor 46b can be selectively coupled by means of an additional electrical switching element 70, i.e. the energy storage element 44b and the electrical resistor 46b are only connected to the DC voltage source 50 when both the electrical switching element 54 and the electrical switching element 70 are closed.

[0196] The electrical switching element 70 is switched by means of the state control unit 62.

[0197] Thus, depending on the electrical resistance and / or temperature of the actuating element 34, the energy storage element 44b and the electrical resistance 46b can be used.

[0198] Furthermore, the energy storage element 44b and the electrical resistance 46b can be used depending on an environmental parameter U determined by means of the environmental sensor 63a and / or depending on a second operating parameter B2 determined by means of the machine status sensor 63b.

[0199] Figure 13 Figure 1 shows an additional, alternative embodiment of the actuator unit 32 in the form of an electrical circuit diagram. The following discussion focuses solely on the differences compared to the aforementioned embodiments. Identical or corresponding elements are designated with the same reference numerals.

[0200] In contrast to the embodiment according to Figure 11 is in the embodiment according to Figure 13 The voltage converter 52 is no longer adjustable. This means that the voltage converter 52 always sets the voltage of the energy storage unit 44 to a fixed value.

[0201] Another difference is that an adjustable electrical resistor 72 is provided in series with the electrical resistor 46. This is set by means of the state control unit 62.

[0202] As before, this can be done depending on an environmental parameter U determined by means of the environmental sensor 63a and / or depending on a resistance determined by means of the current measuring unit 58 and the voltage measuring unit 60 and / or depending on a temperature determined by means of the current measuring unit 58 and the voltage measuring unit 60 and / or depending on a second operating parameter B2 determined by means of the machine status sensor 63b.

[0203] In summary, the embodiments are characterized by Figures 10 and 12 through an energy storage unit 44 with adjustable capacity.

[0204] The control circuits 42 according to Figures 12 and 13They also have an adjustable electrical resistance 46, 46a, 46b, 72.

[0205] Furthermore, in the control circuits 42 according to Figures 10 and 13 The voltage converter 52 is adjustable so that a storage voltage of the energy storage unit 44 can be set.

[0206] In all control circuits 42, the electrical switching element 45 is also adjustable with regard to its actuation time.

[0207] In all the aforementioned embodiments, the actuator 31 can be operated by means of a method for operating an actuator of an emergency brake unit.

[0208] The environmental sensor 63a is used to record an environmental parameter U, in this case the ambient temperature.

[0209] Furthermore, in all the aforementioned embodiments, the electrical resistance and / or temperature of the actuating element 34 are detected by means of the current measuring unit 58 and the voltage measuring unit 60. These can be collectively referred to as the first operating parameter B1 of the actuator 31.

[0210] In all embodiments, it is also provided that a second operating parameter B2 of the tool 8 equipped with the actuator 31 is detected by means of the machine condition sensor 63b, in this case the rotational speed.

[0211] Based on this, in all embodiments the actuator 31 is operated depending on the ambient parameter U, the first operating parameter B1, and the second operating parameter B2. This means that an actuation current parameter SP for the actuating element 34 is set depending on the ambient parameter U, the first operating parameter B1, and the second operating parameter B2.

[0212] In the embodiments according to Figures 12 and 13 For this purpose, the electrical resistance acting between the energy storage unit 44 and the actuating element 34 is set as a function of the ambient parameter U, the first operating parameter B1 and the second operating parameter B2.

[0213] In the embodiments according to Figures 10 and 12 For this purpose, the capacity of the energy storage unit 44 is set depending on the environmental parameter U, the first operating parameter B1 and the second operating parameter B2.

[0214] In the embodiments according to Figures 10 and 11 Furthermore, the storage voltage of the energy storage unit 44 is set via the adjustable voltage converter 52 depending on the ambient parameter U, the first operating parameter B1 and the second operating parameter B2.

[0215] Furthermore, in all embodiments the actuation current parameter SP is set by setting an actuation time of the switching element 54 depending on the environmental parameter U, the first operating parameter B1 and the second operating parameter B2.

[0216] Furthermore, in the embodiments according to Figure 11 , 12 and 13 The actuating element 34 is tempered by means of the tempering device 64 to a temperature above a current ambient temperature and below a switching temperature of the actuating element 34.

[0217] It has been stated here that the actuation current parameter SP is set depending on the ambient parameter U, the first operating parameter B1, and the second operating parameter B2. However, it is understood that only one or a pair of these parameters can be used.

[0218] In all the above embodiments, the emergency brake unit 24 or emergency brake assembly 82 can be operated as follows.

[0219] In a first step, the brake element 29, in this case the brake cam 30, is set in motion by means of the actuating element 34. For this purpose, the actuating element 34 is shortened by applying a corresponding current. As already explained, this causes the brake cam 30 to move in the embodiments according to Figures 3 and 6 until 9 The actuating pin 40 is subjected to a pressure force. In the embodiment according to Figure 4 The second end 34b of the actuating element 34 is directly attached to the brake cam 30 and exerts a tensile force on it.

[0220] In all embodiments, this brings the brake cam 30 into contact with the saw blade 20. Since the emergency brake assembly 82 or emergency brake unit 24 is designed to be self-reinforcing, the brake cam 30 is carried along by the saw blade 20 due to this contact. This causes the brake cam 30 to press the saw blade 20 against the pressure element 28 with increasing force until the saw blade 20 comes to a standstill.

[0221] In this context, after the initial movement of the brake cam 30, a motion coupling between the actuating element 34 and the brake element 29, i.e., the brake cam 30, is terminated or released. This occurs in the embodiments according to Figures 3 and 6 until 9 by the brake-element-side end 41 of the actuating pin 40 lifting off from the brake element 29, i.e., from the brake cam 30. In the embodiment according to Figure 4This is achieved by the brake cam 30 moving so far that the actuating element 34 is no longer under mechanical tension and therefore can no longer exert a tensile force on the brake element 29, i.e. the brake cam 30.

[0222] This means that the actuating element 34 can be returned to its initial position, i.e., its unactuated position, after sufficient cooling. For this, the thermally induced microstructure transformation is reversed. The resetting occurs independently of the brake element 29, i.e., the brake cam 30, which can be reset separately from the actuating element 34.

[0223] The foregoing explanations refer to a sawing device 10 in the form of a miter saw. However, it is understood that the design as a miter saw is only an example and the foregoing statements also apply to sawing devices of other designs, e.g., band saws. Reference symbol list

[0224] 8 Motor-driven tool 10 Sawing device 12 Base part 14 Support surface 16 Workpiece 18 Swivel device 18a First section 18b Second section 20 Saw blade 22 Handle 24 Emergency brake unit 26 Brake caliper 28 Pressure element 29 Brake element 30 Brake cam 31 Actuator 32 Actuator unit 34 Actuating element 34a First end 34b Second end 35 Holding structure 36 Shape memory alloy 37 Spring element 38 Slide 39 Actuator housing 40 Actuating pin 40a Pin shaft 41 Brake element end of the actuating pin 42 Control circuit 44 Electrical energy storage unit 44a Electrical energy storage element 44b Electrical energy storage element 45 Electrical switching element 46 Electrical resistor 46a Electrical resistor 46b electrical resistance 48 charging circuit 50 DC voltage source 52 voltage converter 54 further electrical switching element 56 trip control unit 58 current measuring unit 60 voltage measuring unit 62 state control unit 63a ambient sensor 63b machine state sensor 64 heating circuitTemperature control device 66 Heating controller 68 Electrical switching element 70 Electrical switching element 72 Electrical resistance 74 Elastic bearing element 76 Articulated arm 78 Carrier plate 80 Intermediate element 82 Emergency brake assembly 84 First sleeve 84 Second sleeve A Dimension B1 First operating parameter B2 Second operating parameter I BE Current through the actuating element L BE Length of the actuating element R BE Electrical resistance of the actuating element R LS Electrical resistance of the charging circuit SP Actuating current parameter U Ambient parameter U BE Voltage drop across the actuating element,

Claims

1. Emergency brake assembly (82) for a motor-driven tool (8), comprising a holding structure (35), a brake element (29) rotatably mounted on the holding structure (35), in particular a brake cam (30), and a wire-shaped actuating element (34) comprising a shape memory alloy (36), wherein a first end (34a) of the actuating element (34) is attached to the holding structure (35) and a second end (34b) of the actuating element (34) is coupled to the brake element (29) in terms of drive.

2. Emergency brake assembly (82) according to claim 1, wherein the second end (34b) of the actuating element (34) is attached to the brake element (29).

3. Emergency brake assembly (82) according to claim 1, wherein the second end (34b) of the actuating element (34) is coupled to the brake element (29) via at least one intermediate element (80).

4. Emergency brake assembly (82) according to claim 3, wherein the at least one intermediate element (80) comprises a slide (38) movably mounted on the holding structure (35).

5. Emergency brake assembly (82) according to claim 4, wherein the slide (38) is mounted on the holding structure (35) so as to be movable in translation via a sliding guide, and / or wherein the slide is movably mounted on the holding structure (35) via at least one articulated arm (76), and / or wherein the slide (38) is connected to the holding structure (35) via a resilient bearing element (74).

6. Emergency brake assembly (82) according to any of claims 3 to 5, wherein the at least one intermediate element (80) comprises a plunger or an actuating pin (40) having a brake-element-side end (41), wherein the brake-element-side end (41) of the plunger or actuating pin (40) is positioned against the brake element (29) or can be placed against the brake element (29).

7. Emergency brake assembly (82) according to any of the preceding claims, wherein the actuating element (34) is guided by means of a guide element.

8. Emergency brake assembly (82) according to any of the preceding claims, further comprising a spring element (37) which directly or indirectly spring-loads the actuating element (34) in a direction corresponding to a tensile load on the actuating element (34).

9. Emergency brake assembly (82) according to any of the preceding claims, wherein the holding structure (35) is formed by an actuator housing (39) and / or a brake calliper (26), in particular wherein a control unit for the actuating element (34) is integrated at least in portions into the actuator housing (39).

10. Emergency brake assembly (82) according to any of the preceding claims, wherein a first sleeve (84a) is provided at the first end (34a) of the actuating element (34) and the first end (34a) of the actuating element (34) is attached to the holding structure (35) via the first sleeve (84a).

11. Emergency brake assembly (82) according to any of the preceding claims, wherein a second sleeve (84b) is provided at the second end (34b) of the actuating element (34) and the second end (34b) of the actuating element (34) is coupled to the brake element (29) in terms of drive via the second sleeve (84b).

12. Emergency brake assembly (82) according to any of the preceding claims, wherein a length (LBE) of the actuating element (34) is less than a dimension (A) of the emergency brake unit (24) along a direction parallel to the length (LBE) of the actuating element (34) and / or wherein a length (LBE) of the actuating element (34) is positioned entirely within a dimension (A) of the emergency brake unit (24) as measured parallel to the length (LBE) of the actuating element (34).

13. Emergency brake assembly (82) according to any of the preceding claims, wherein the actuating element (34) and / or a portion of the holding structure (35) mechanically shields a drive coupling portion of the brake element (29).

14. Method for operating an emergency brake assembly (82) having a movably mounted brake element (29), in particular a brake cam (30), for braking a cutting element of a motor-driven tool (8), wherein the emergency brake assembly (82) further has a wire-shaped actuating element (34) comprising a shape memory alloy (36) and the actuating element (34) is coupled to the brake element (29) in terms of drive, comprising: - setting the brake element (29) in movement by means of the actuating element (34) and - subsequently undoing or terminating a movement coupling between the actuating element (34) and the braking element (29).

15. Method according to claim 14, further comprising: resetting the actuating element (34) to a starting position, wherein the resetting takes place independently of the braking element (29).