Method for operating an emergency brake unit for a motor-driven tool, monitoring unit and emergency brake unit

Abstract

A method for operating an emergency brake unit (26) for a motor-driven tool is described. The emergency brake unit (26) comprises an actuator (34) with an actuating element (36), and at least one electrical energy storage unit (52). The actuating element (36) can be selectively acted upon with electrical energy stored in the energy storage unit (52). The method comprises detecting an energy storage unit state parameter (Z1) which characterizes a state of the energy storage unit (52). Alternatively or additionally, an actuating element state parameter (Z2) is detected which characterizes a state of the actuating element (36). If at least one out of the energy storage unit state parameter (Z1) and actuating element state parameter (Z2) lies outside a respectively associated standard range, a blocking signal is triggered. Furthermore, a monitoring unit (50) for monitoring a state of an emergency brake unit (26) and an emergency brake unit (26) are presented.

Description

[0001] Method for operating an emergency braking unit for a motor-driven tool, monitoring unit and emergency braking unit

[0002] The invention is directed to a method for operating an emergency brake unit for a motor-driven tool. The emergency brake unit comprises an actuator with an actuating element and at least one electrical energy storage unit, which is electrically coupled to the actuating element via an electrical switching element, so that the actuating element can be selectively supplied with electrical energy stored in the energy storage unit by actuating the switching element.

[0003] The invention also relates to a monitoring unit for monitoring the status of an emergency brake unit for a motor-driven tool. The emergency brake unit comprises an actuator with an actuating element and at least one electrical energy storage unit, which is electrically coupled to the actuating element via an electrical switching element, so that the actuating element can be selectively supplied with electrical energy stored in the energy storage unit by actuating the switching element.

[0004] Furthermore, the invention is directed to an emergency brake unit for a motor-driven tool with such a monitoring unit.

[0005] Motor-driven tools with emergency brake units are known from the state of the art. The same applies to emergency brake units. These are used to bring a cutting element, e.g., a saw blade, of the tool to a standstill if contact occurs during operation.

[0006] AS: TOP of a user being threatened or detected by the cutting element. This prevents injuries or reduces their severity.

[0007] In this context, an actuating element is understood to be the element of the actuator by means of which the movement is generated that the actuator requires to actuate a system actuated by the actuator, in this case the braking system. One well-known type of actuating element comprises a shape memory alloy. Its function 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. Actuating elements comprising a shape memory alloy are often formed as wires that shorten due to the thermally activated lattice transformation. Another well-known type of actuating element is a solenoid, in which a plunger can be displaced by electrically controlling a magnetic coil.

[0008] Such actuators are preferably used in reversible emergency braking units, i.e., emergency braking units that can be used multiple times to bring the cutting element to a standstill. It goes without saying that in reversible emergency braking units, the actuator must be capable of being actuated multiple times with consistently high reliability.

[0009] The invention is therefore based on the object of further improving known emergency braking units.

[0010] The object is achieved by a method for operating an emergency brake unit for a motor-driven tool. The emergency brake unit has an actuator with an actuating element and at least one electrical energy storage unit, which is electrically coupled to the actuating element via an electrical switching 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 method comprises: - detecting an energy storage unit state parameter that characterizes a state of the energy storage unit and / or an actuating element state parameter that characterizes a state of the actuating element,

[0011] - comparing the detected energy storage unit state parameter with an energy storage unit threshold value that limits a standard range assigned to the energy storage unit state parameter, and / or comparing the detected actuating element state parameter with an actuating element threshold value that limits a standard range assigned to the actuating element state parameter (Z2),

[0012] - Triggering a blocking signal if at least one of the detected energy storage unit state parameters and the detected actuating element state parameters is outside the respectively assigned standard range.

[0013] By means of the method according to the invention, a state of at least one of the energy storage unit and the actuating element is monitored. Only if the energy storage unit state parameter or actuating element state parameter describing the state lies within a respective associated standard range, which can also be referred to as the normal range, can the actuator of the emergency brake unit, and thus the emergency brake unit as a whole, be operated. Otherwise, operation of the actuator and thus the emergency brake unit is blocked. This increases the reliability of the emergency brake unit, since it can only be operated if a corresponding state has been detected for at least one of the energy storage unit and the actuating element. This applies particularly if the emergency brake unit is a multi-trigger emergency brake unit.In this variant, it is ensured that at least one of the energy storage unit and the actuating element is in a suitable state each time the device is triggered. In the case of emergency brake units that can be triggered multiple times, it can also be said in this context that an aging state or wear state resulting from previous triggerings is monitored. It is understood that operation of the emergency brake unit is only possible depending on a state parameter that was previously recorded or received. There are several alternatives for triggering a blocking signal. In a first alternative, such a blocking signal is actively triggered when the energy storage unit state parameter and / or the actuating element state parameter lies outside the respectively assigned standard range. In a case in which all recorded state parameters, ieIf the energy storage unit state parameters and / or the actuating element state parameters are within the standard range, no such blocking signal is triggered. Optionally, an active or explicit release signal can be triggered in this case. In a second alternative, an active release signal is always triggered when all detected state parameters, i.e. the energy storage unit state parameters and / or the actuating element state parameters, are within the standard range. A blocking signal can be triggered by simply no longer triggering an release signal. It is also understood that, depending on the type of state parameter, the assigned threshold value can limit the standard range upwards and / or downwards.

[0014] The tool can be a hand-held tool, which can also be called a hand tool, a semi-stationary tool, or a stationary tool.

[0015] In a preferred embodiment, the tool is a saw. This can be a hand saw, a semi-stationary saw, or a stationary saw. An example of a hand saw is a portable circular saw. An example of a semi-stationary saw is a portable table saw. An example of a stationary saw is a sliding table saw.

[0016] The actuating element may comprise a lifting magnet or a shape memory alloy, e.g. in wire form.

[0017] 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 designed as a component of the actuator or as a component of the tool. The only important thing is that the electrical energy storage unit is electrically coupled to the actuating element.

[0018] In one variant, the actuator includes a preload element. The method may then additionally include:

[0019] - detecting a prestressing element state parameter that characterizes a state of the prestressing element,

[0020] - comparing the pre-stress element state parameter with a pre-stress element threshold value that limits a standard range associated with the pre-stress element state parameter,

[0021] - Triggering a lock signal when the bias element status parameter is outside the normal range.

[0022] The preload element is particularly designed to transfer the actuating element into a predetermined position or position or to hold it there when the actuating element is not actuated. The preload element is designed, for example, as a spring. In this variant, the state of the preload element is thus monitored. This ensures that the actuator and the emergency brake unit equipped with it are only operated when the preload element is in a suitable state. Consequently, the reliability of the emergency brake unit is increased.

[0023] The preload element state parameter can describe a conductivity of the preload element, and the preload element threshold value can describe a minimum permissible conductivity. The conductivity of the preload element is expediently measured between two ends of the preload element. In this example, the preload element can also be designed as a spring, in particular as a coil or leg spring made of an electrically conductive material such as metal. In this context, reduced or lacking conductivity can be understood as an indication of structural damage to the preload element. In such a case, the operation of the actuator and thus of the emergency brake unit is prevented. An illustrative example of this is a broken metal coil spring, whose conductivity is greatly reduced or no longer present due to the break.

[0024] The energy storage unit status parameter can also describe the number of actuations of the energy storage unit that have already occurred, and the energy storage unit threshold value can describe the maximum number of permissible actuations. Alternatively or additionally, the actuation element status parameter can describe the number of actuations of the actuation element that have already occurred, and the actuation element threshold value can describe the maximum number of permissible actuations. Thus, actuations of the energy storage unit and / or the actuation element are counted and compared with a maximum number.

[0025] The maximum number may be specified by the manufacturer of the actuator or emergency braking unit as a fixed maximum. This value is therefore fixed and cannot be changed directly or indirectly by the user.

[0026] Alternatively or additionally, the maximum number can be calculated depending on one or more state parameters of the actuating element and / or the energy storage unit. This results in a situational maximum number that depends on the specific aging and / or wear of the actuator and / or the emergency brake unit. This can be influenced at least indirectly by usage behavior. State parameters that can be used for this purpose include the energy storage capacity of the energy storage unit or the electrical resistance of an actuating element that comprises a shape memory alloy, e.g., a wire made of a shape memory alloy.In a further alternative, the maximum number is not calculated as a direct function of one or more state parameters of the actuating element and / or the energy storage unit, but rather using a model that calculates a maximum number based on one or more state parameters of the actuating element and / or the energy storage unit. Such a model can be constructed based on empirical data from the operation of the actuator and / or the emergency braking unit as a whole. The empirical data includes, for example, a number of previous triggerings, historical current intensities and energization periods during historical triggerings, a downtime during which the emergency braking unit was out of operation, and / or a downtime between two safety tests of the emergency braking unit. In all variants, it is ensured that the emergency braking unit either functions with high reliability or that a blocking signal is triggered.

[0027] It is understood that the threshold value that defines the maximum number of permissible actuations can also be determined as the smallest number of maximum permissible actuations from the fixed maximum number and the situational maximum number.

[0028] According to one variant, the actuating element state parameter describes a position or a position difference of the actuating element, and the actuating element threshold value describes a target position or a target position difference. A position difference is, for example, a stroke of the actuating element. The position can be an initial position or zero position of the actuating element. Position monitoring can be used to determine aging or wear of the actuating element, thus determining whether reliable operation of the emergency braking unit is still possible. In a case where the actuating element comprises a lifting magnet, the positions of the associated plunger can be determined via the inductance of the magnetic coil.

[0029] Alternatively or additionally, it is possible for the actuator state parameter to describe the electrical resistance of the actuator, and for the actuator threshold value to describe the maximum permissible electrical resistance. The electrical resistance is considered an indicator of wear and / or aging. This is particularly true in a case where the actuator comprises a shape memory alloy. Structural fatigue of the shape memory alloy can be inferred from an increase in electrical resistance. Temperature influences on the electrical resistance can be mathematically eliminated. In a case where the actuator comprises a solenoid, damage to electrical cables, e.g., a broken cable, can be detected via increased electrical resistance.

[0030] According to one embodiment, the actuating element state parameter describes an actuation latency of the actuating element, and the actuating element threshold value describes a maximum permissible actuation latency. Actuation latency is understood to be the time between the closing of the switching element and the start of movement or the reaching of a defined position by the actuating element. The defined position is, for example, a target position. In the case where the actuating element comprises a shape memory alloy, functional fatigue is characterized by the loss of shape memory and is usually characterized by a significant increase in transformation temperatures, which manifests itself in an extended time interval between the onset of current flow and the onset of the phase transformation, i.e., the change in length.The point at which the shape memory alloy wire begins to change its length can be determined, for example, by the maximum electrical resistance of the shape memory alloy wire. This provides a simple way to determine any deterioration in the actuator's response.

[0031] Furthermore, the actuator state parameter can describe a voltage drop across the actuator, and the actuator threshold can describe a maximum permissible voltage drop. Several variants are conceivable here. On the one hand, the voltage drop itself can be used as an indicator of aging or wear. This is particularly the case if the associated current is subject to only minor fluctuations or is known. Alternatively, it is conceivable to use the voltage drop to calculate the electrical resistance.

[0032] In one variant, the actuating element state parameter describes an actuating force of the actuating element, and the actuating element threshold value describes a minimum permissible actuating force. Alternatively or additionally, the preload element state parameter describes a preload force of the preload element, and the preload element threshold value describes a minimum permissible preload force. This ensures that the actuating element and / or the preload element either have an actuating force or preload force sufficient for reliable operation of the emergency braking unit, or that a blocking signal is triggered. Overall, this results in a high level of reliability for the emergency braking unit.

[0033] In another variant, the energy storage unit status parameter describes a storage capacity of the energy storage unit, and the energy storage unit threshold value describes a permissible minimum storage capacity. As already explained, energy stored in the energy storage unit is used to actuate the actuating element. This ensures that the storage capacity, which may be subject to aging or wear, is sufficient for reliable operation of the emergency braking unit.

[0034] At least one of the energy storage unit status parameters, the actuator status parameters, and the preload element status parameters can be recorded during a test routine. Alternative terms for a test routine are test operation, test sequence, test routine, and self-test. The test routine must be distinguished from the operation of the emergency braking unit. The test routine is executed before actual operation or before a predetermined operating phase to ensure that the recorded status parameters are within the normal range. Otherwise, operation is not possible. The test routine is performed, for example, after each activation of the emergency braking unit, after each use of the tool, before each use of the tool, or regularly during work breaks or temporary interruptions in the operation of the tool.

[0035] As part of a test routine, the energy storage unit can be fully or partially charged and then discharged. This allows the energy storage unit's storage capacity to be determined. In a case where the actuating element comprises a shape memory alloy in the form of a wire, it is possible to apply a comparatively small current, i.e., relatively low energy, to the shape memory alloy as part of a test routine and measure a stroke or voltage drop after a certain period of time. These values ​​can be compared with the respective assigned target values.

[0036] The test routine may also include checking whether a cutting element is mounted in the tool. As already explained, the cutting element is, for example, a saw blade.

[0037] Furthermore, the test routine can include checking a mechanical component of the emergency brake unit for wear. In this context, for example, the wear status of the emergency brake unit's brake pads can be determined. The wear status of the brake pad(s) can be determined, for example, by applying the brake to the capacitively coupled saw blade. The thickness of the brake pad influences the capacitive coupling between the saw blade and the brake, allowing conclusions to be drawn about the wear of the brake pad.

[0038] In one variant, the method further comprises providing at least one of the energy storage unit state parameters, the actuating element state parameters, and the preload element state parameters to a user. An aggregated overall state composed of at least two of the energy storage unit state parameters, the actuating element state parameters, and the preload element state parameters can also be provided. The provision can be made either via an interface that is not directly readable by a human, e.g., via Bluetooth or Wi-Fi. For this purpose, a smartphone or other electronic device can be coupled to an interface of the emergency braking unit. Alternatively, a human-readable communication interface, e.g., a display, can be provided on the emergency braking unit or on the tool equipped with it.In an illustrative example, this method can be used to communicate to a user whether the emergency brake unit has already been triggered and / or whether it is still available. Based on this, the user can plan their work with the tool more effectively. Furthermore, confidence in the reliability of the emergency brake unit and the tool equipped with it is increased.

[0039] The method may also include triggering a warning signal if at least one of the energy storage unit status parameters, the actuating element status parameters, and the preload element status parameters is within the respective assigned standard range and within an assigned warning range. In particular, the warning range is at one end of the standard range, which corresponds to comparatively high wear or comparatively high aging. The user of the emergency braking unit and the tool equipped with it thus receives a warning that operation of the emergency braking unit may soon no longer be possible and can thus prepare accordingly.

[0040] Additionally, the object is achieved by a monitoring unit for monitoring the state of an emergency braking unit for a motor-driven tool. The emergency braking unit has an actuator with an actuating element and at least one electrical energy storage unit, which is electrically coupled to the actuating element 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 monitoring unit comprises at least one state sensor, which is designed to detect an energy storage unit state parameter that characterizes a state of the energy storage unit. Alternatively or additionally, the state sensor is designed to detect an actuating element state parameter that characterizes a state of the actuating element.In addition, the monitoring unit comprises a memory unit on which at least one of an energy storage unit threshold value and an actuating element threshold value is stored, which limits a respective assigned standard range. Furthermore, the monitoring unit comprises a computing unit configured to compare the energy storage unit state parameter detected by the state sensor with the energy storage unit threshold value. Alternatively or additionally, the computing unit is configured to compare the detected actuating element state parameter with the actuating element threshold value. Furthermore, the monitoring unit comprises a communication interface for triggering a blocking signal. Thus, the monitoring unit can be used to monitor the state of at least one of the energy storage unit and the actuating element.The actuator of the emergency braking unit, and thus the emergency braking unit as a whole, can only be operated if the state parameter describing the state lies within an associated standard range, which can also be referred to as the normal range. Otherwise, operation of the actuator and thus of the emergency braking unit is blocked. This increases the reliability of the emergency braking unit, as it can only be operated if a corresponding state within the respective assigned standard range has been recorded for all state parameters to be recorded. This applies in particular if the emergency braking unit is a multi-triggerable emergency braking unit. This variant ensures that the emergency braking unit is in a suitable state each time it is triggered.In the case of emergency brake units that can be triggered multiple times, it can also be said in this context that the aging or wear condition resulting from previous triggerings is monitored. Regarding the triggering of a blocking signal, the alternatives already explained in connection with the method according to the invention are again available. Overall, the monitoring unit increases the reliability of the associated emergency brake unit.

[0041] If the state to be detected by the monitoring unit relates to the actuation processes of the energy storage unit, the state sensor can be an electrical current sensor or an electrical voltage sensor that detects a current flowing across a system boundary of the energy storage unit or a voltage drop across the energy storage unit over time. Such current and voltage curves can be evaluated to determine the number of actuation processes. In the case of the detected electrical current, a current flow direction can also be taken into account. In this context, for example, crossings above certain threshold values ​​are counted and used as indicators of actuation processes.If the condition to be detected by the monitoring unit concerns the storage capacity of the energy storage unit, the condition sensor can be an electrical current sensor that detects a current flowing across a system boundary of the energy storage unit over time. To determine the storage capacity, the energy storage unit can be fully charged and fully discharged once, e.g., as part of a test routine. The storage capacity can be determined from the resulting current curve.

[0042] If the condition to be detected by the monitoring unit concerns the voltage drop across the actuating element, the condition sensor may be an electrical voltage sensor that detects a voltage drop across the actuating element over time.

[0043] If the condition to be detected by the monitoring unit concerns the electrical resistance of the actuating element, the condition sensor can be a combination of an electrical current sensor and an electrical voltage sensor. This allows a current flowing across a system boundary of the actuating element and a voltage drop across the actuating element to be detected over time. Based on these values, the electrical resistance can be calculated.

[0044] If the state to be detected by the monitoring unit relates to the actuation processes of the actuating element, the state sensor can also be an electrical current sensor or an electrical voltage sensor that detects a current flowing across a system boundary of the actuating element or a voltage drop across the actuating element over time. Such current and voltage curves can be evaluated to determine the number of actuation processes. In this context, for example, crossings above certain threshold values ​​are counted and used as indicators of actuation processes. Alternatively or additionally, the current and voltage curves can be used to determine the aging state of the actuating element, for example by counting crossings above certain current or voltage threshold values ​​and using them as indicators of the aging of the actuating element.If the condition to be detected by the monitoring unit concerns the position or position difference of the actuating element, the condition sensor can be a position sensor. This can include both position sensors that can detect an absolute position and position sensors that can only detect a relative position.

[0045] If the condition to be detected by the monitoring unit concerns an actuating force of the actuating element, the condition sensor may be a force sensor.

[0046] If the state to be detected by the monitoring unit concerns the actuation latency of the actuating element, the state sensor can also be an electrical current sensor or an electrical voltage sensor that detects a current flowing across a system boundary of the actuating element or a voltage drop across the actuating element over time. Such current and voltage curves can be used to determine the actuation latency. Optionally, the aforementioned position sensor and / or force sensor can also be used.

[0047] Alternatively or additionally, the status sensor can be a trigger control unit for detecting that a user is coming into contact with the saw blade or that such contact is imminent, comprising, for example, a capacitive sensor. In this way, the time span from the triggering of the emergency brake unit to the contact of the brake, in particular the brake cam, with the saw blade—i.e., the actuation latency of the entire emergency brake unit—can be determined, for example, during the test routine.

[0048] The monitoring unit may also comprise a condition sensor configured to determine a condition of a biasing element of the actuator of the emergency brake unit.

[0049] If the condition to be detected by the monitoring unit concerns the conductivity of the preload element, the condition sensor can be an electrical current sensor that detects a current flowing across a system boundary of the preload element. The conductivity can be determined based on the magnitude of the measured current. If the condition to be detected by the monitoring unit concerns a preload force of the preload element, the condition sensor can be a force sensor.

[0050] It is understood that the condition sensor may also include any combination of the sensors mentioned.

[0051] The object is further achieved by an emergency brake unit for a motor-driven tool. The emergency brake unit comprises a monitoring unit according to the invention. Thus, the state of at least one of the energy storage unit and the actuating element, i.e., the functional core elements of the emergency brake unit, can be monitored. Only if the state parameter describing the state lies within an associated standard range, which can also be referred to as the normal range, can the actuator of the emergency brake unit, and thus the emergency brake unit as a whole, be operated. Otherwise, operation of the actuator, and thus of the emergency brake unit, is disabled. This increases the reliability of the emergency brake unit.

[0052] It is understood that the effects and advantages mentioned with regard to one of the inventive method, the inventive monitoring unit and the inventive emergency braking unit also apply to any other of the inventive method, the inventive monitoring unit and the inventive emergency braking unit.

[0053] The invention is explained below using various embodiments shown in the accompanying drawings. They show:

[0054] Figure 1 shows a sawing device with an emergency brake unit according to the invention, which is equipped with a monitoring unit according to the invention and an actuator, wherein the emergency brake unit can be operated by means of a method according to the invention,

[0055] Figure 2 shows the sawing device from Figure 1, with a housing part and a protective cover omitted, Figure 3 shows a section through the sawing device from Figure 2 along the plane III,

[0056] Figure 4 in a view along the direction IV in Figure 2 the emergency brake unit in an isolated representation,

[0057] Figure 5 shows an alternative embodiment of the emergency brake unit in a view corresponding to Figure 3,

[0058] Figure 6 in a view corresponding to Figure 3 shows another alternative

[0059] Design of the emergency brake unit, and

[0060] Figure 7 shows the emergency braking unit according to the invention as well as its actuator and the monitoring unit according to the invention in a schematic view.

[0061] Figures 1 and 2 show a motor-driven tool 10, which in the example shown is a sawing device 12, more precisely a miter saw.

[0062] The sawing device 10 comprises a base part 14, which has a support surface 16 for a workpiece 18. The workpiece 18 is to be understood as exemplary.

[0063] The sawing device 12 further comprises a pivoting device 20, which is pivotally mounted on the base part 14 at a first section 20a. A disk-shaped saw blade 22 is mounted on a second section 20b, which is spaced apart from the first section 20a. Furthermore, a handle 24 is provided on the second section 20b.

[0064] A user of the sawing device 12 can thus, by means of the handle 24, bring the saw blade 22 in a rotating state into interaction with the workpiece 18 mounted on the support surface 16, so that the workpiece is sawn into or sawn off.

[0065] The sawing device 12, i.e., the motor-driven tool 10, is further equipped with an emergency braking unit 26. The emergency braking unit 26 is configured to brake the saw blade 22 to a standstill if, while the saw blade 22 is rotating, it is detected that a user is coming into contact with the saw blade 22 or that such contact is imminent.

[0066] In this context, the saw blade 22 is used as a capacitive sensor element, meaning that the electrical capacitance of the saw blade 22 is continuously measured. If the electrical capacitance is outside a predetermined normal range, contact is detected. This example is intended to be exemplary. Other methods, such as optical ones, for detecting that a user is coming into contact with the saw blade 22 or that such contact is imminent are also conceivable.

[0067] The emergency brake unit 26 can be seen in detail in several variants in Figures 3 to 6.

[0068] In all variants, the emergency brake unit 26 has a brake caliper 28 which engages over an edge of the saw blade 22, so that a pressure element 30 provided on the brake caliper 28 is arranged on a first axial side of the saw blade 22 and a brake cam 32 rotatably mounted on the brake caliper 28 is arranged on a second axial side of the saw blade 22.

[0069] The brake cam 32 is coupled to an actuator 34, by means of which the brake cam 32 can be selectively rotated such that it presses the saw blade 22 against the pressure element 30 and consequently brakes it to a standstill.

[0070] In the variant of Figures 3 and 4, the actuator 34 comprises an actuating element 36 comprising a shape memory alloy 38. Specifically, the actuating element 36 is formed as a wire made of the shape memory alloy 38.

[0071] The actuating element 36 is attached at a first end 36a to a mounting receptacle. The mounting receptacle can be part of the brake caliper 28 or part of a support structure attached to the brake caliper 28. The other end 36b of the actuating element 36 is attached to a carriage 40, which is mounted for translational displacement relative to the brake caliper 28. The carriage 40 is subjected to a force by means of a preloading element 42 in a direction that corresponds to a tensile load on the actuating element 36. In this case, the preloading element 42 is designed as a spiral spring.

[0072] Furthermore, the carriage 40 is coupled to the brake cam 32 via an actuating pin 44.

[0073] If the actuating element 34 is subjected to a sufficient electric current, a thermally induced lattice transformation of the shape memory alloy 38 occurs, causing the actuating element 36 to shorten. This results in a displacement of the carriage 40 and the actuating pin 44 to the right in Figure 3, i.e., against the preload of the preload element 42. As a result, the brake cam 32 is brought into engagement with the saw blade 22 and brakes it to a standstill.

[0074] Figure 5 shows an alternative embodiment of the actuator 34. In this embodiment, the first end 36a of the actuating element 36, which is designed as a wire made of shape memory alloy 38, is fixed relative to the brake caliper 28 as usual.

[0075] In contrast to the variant shown in Figures 3 and 4, however, the second end 36b is attached directly to the brake cam 32. The brake cam 32 is subjected to force by means of a preload element 42. The loading direction again corresponds to a tensile loading direction for the actuating element 36.

[0076] The preload element 42 is again a spiral spring.

[0077] If, in the variant shown in Figure 5, the actuating element 36 is subjected to a sufficient electric current, a thermally induced lattice transformation of the shape memory alloy 38 occurs, causing the actuating element 36 to shorten. This results in a rotation of the brake cam 32, so that it engages the saw blade 22 and brakes it to a standstill. In Figure 5, the brake cam 30 rotates clockwise when the emergency brake is triggered. Figure 6 shows a further variant in which the brake cam 32 corresponds to the brake cam 32 shown in Figure 3.

[0078] The essential difference to the variants from Figures 2 to 5 is that the actuating element 36 is now designed as a lifting magnet 46, which acts with its plunger 48 directly on the brake cam 32.

[0079] If, in this variant, the actuating element 36, i.e., the lifting magnet 46, is supplied with an electric current of sufficient magnitude, the plunger 48 moves to the right in Figure 6. This results in a clockwise rotation of the brake cam 32, as shown in Figure 6, so that it engages the saw blade 22 and brakes it to a standstill.

[0080] In all variants, the emergency brake unit 26 includes a monitoring unit 50, which is shown only schematically in Figures 3 to 6. This can be seen in detail together with the other components of the actuator 34 in Figure 7.

[0081] The emergency brake unit 26, the actuating element 36 of which was shown in Figures 3 to 6, further comprises an electrical energy storage unit 52, which may be designed as a battery or capacitor.

[0082] The electrical energy storage unit 52 is coupled to the actuating element 36 via an electrical switching element 54, so that the actuating element 36 can be selectively supplied with electrical energy stored in the energy storage unit 52 by actuating the switching element 54. In other words, by actuating the switching element 54, depending on the embodiment, the shape memory alloy wire 38 or the lifting magnet 46 is energized. A quantity of charge provided in the energy storage unit 52 is used for this purpose.

[0083] The monitoring unit 50 is configured to monitor a state of the emergency braking unit 26. For this purpose, the monitoring unit 50 comprises a first state sensor 56a configured to detect an energy storage unit state parameter ZI that characterizes a state of the energy storage unit 52.

[0084] In the illustrated embodiment, the monitoring unit 50 further comprises a second state sensor 56b which is designed to detect an actuating element state parameter Z2 which characterizes a state of the actuating element 36.

[0085] Furthermore, in the present example, the monitoring unit 50 comprises a third state sensor 56c, which is designed to detect a preload element state parameter Z3 that characterizes a state of the preload element 42.

[0086] All condition sensors 56a, 56b, 56c are signal-technically coupled to a computing unit 58 of the monitoring unit 50.

[0087] The computing unit 58 is also signal-technically coupled to a storage unit 60.

[0088] In this context, the computing unit 58 is designed to calculate the energy storage unit values ​​detected by the respective associated state sensor 56a, 56b, 56c.

[0089] To receive state parameter ZI, actuator state parameter Z2 and preload element state parameter Z3.

[0090] Furthermore, the computing unit 58 is configured to receive from the memory unit 60 an energy storage unit threshold value S1 associated with the energy storage unit state parameter Z1, an actuating element threshold value S2 associated with the actuating element state parameter Z2, and a bias element threshold value S3 associated with the bias element state parameter Z3. The energy storage unit threshold value S1, the actuating element threshold value S2, and the bias element threshold value S3 are stored in the memory unit 60.

[0091] The energy storage unit threshold value S1 defines a standard range of the energy storage unit state parameter Z1. The actuating element threshold value S2 defines a standard range of the actuating element state parameter Z2. The preload element threshold value S3 defines a standard range of the preload element state parameter Z3.

[0092] Furthermore, the computing unit 58 is designed to compare the energy storage unit state parameter ZI, the actuating element state parameter Z2 and the preload element state parameter Z3, which are detected by means of the respectively assigned state sensor 56a, 56b, 56c, with the respectively associated ones from the energy storage unit threshold value S1, the actuating element threshold value S2 and the preload element threshold value S3.

[0093] In addition, the monitoring unit 50 comprises a communication interface 62 which is signal-coupled to the computing unit 58.

[0094] As will be explained in more detail later, a blocking signal can be triggered via the communication interface 62, which causes the actuator 34 and thus the emergency brake unit 26 to be inoperable.

[0095] In the illustrated example, the first state sensor 56a comprises an electrical current sensor and an electrical voltage sensor. Thus, a current flowing across a system boundary of the energy storage unit 52 and a voltage drop across the energy storage unit 52 can be detected over time.

[0096] Based on these current and voltage curves, a number of actuation processes can be determined by the computing unit 58. In this case, the measured current exceeds a specific threshold value provided by the storage unit 60 and is used as indicators of actuation processes.

[0097] In addition, the computing unit 58 is designed to determine a storage capacity of the energy storage unit 52 based on the detected current profile.

[0098] The second state sensor 56b also includes an electrical current sensor and an electrical voltage sensor. Thus, a current flowing across a system boundary of the actuating element 36 and a voltage drop across the actuating element 36 can be detected over time.

[0099] In this context, the voltage drop itself can be used to monitor the condition of the actuating element 36.

[0100] Furthermore, an electrical resistance of the actuating element 36 can be calculated based on the determined voltage curve and the determined current curve, which can be used as the actuating element state parameter Z2.

[0101] As already explained in connection with the energy storage unit 52, a number of actuation processes can also be determined for the actuating element 36 based on the current and voltage curves by means of the computing unit 58.

[0102] In the illustrated embodiment, the second state sensor 56b further comprises a position sensor, by means of which a position of the second end 36b of the actuating element 36 in the form of a wire made of shape memory alloy 38 can be detected. If the actuating element 36 is designed as a lifting magnet 46 (see Figure 6), a position of the plunger 48 can be detected by means of the position sensor.

[0103] The second state sensor 56b also includes a force sensor. The force sensor can detect an actuation force of the actuation element 36. The current sensor or the voltage sensor, in combination with the position sensor or the force sensor, can also detect an actuation latency of the actuation element 36. In this case, the voltage sensor or the current sensor detects a desired start of actuation in the form of a voltage change or a current change. The position sensor or the force sensor detects an actual start of movement of the actuation element 36. The intervening time period is the actuation latency. In this context, the computing unit 58 is configured to perform the above steps for calculating the actuation latency.

[0104] Alternatively, the actuation latency can be determined using a state sensor, which is or includes a trigger control unit 55. This is designed to detect, during operation, that a user is coming into contact with the saw blade 22 or that such contact is imminent. The trigger control unit 55 comprises, for example, a capacitive sensor. The capacitive sensor serves to detect contact or proximity of an electrically conductive medium, such as the skin of a user, with the emergency brake unit 26. The trigger control unit 55 can thus assume a "triggered" and an "untriggered" state. This can be regarded as a trigger control unit state parameter Z4.

[0105] The trigger control unit state parameter Z4 can also be used as part of the test routine. In this context, the trigger control unit 55 is switched from the "untriggered" to the "triggered" state by means of a test trigger, without contact with the saw blade 22 being detected by the capacitive sensor. Rather, the capacitive sensor is used to detect contact between the brake, in particular the brake cam 32, and the saw blade 22. In this way, during the test routine, the time period from the test triggering of the emergency brake unit 26, i.e. from the time at which the trigger control unit state parameter Z4 switches from "untriggered" to "triggered", to the contact of the brake, in particular the brake cam 32, with the saw blade 22, i.e. from the time at which the trigger control unit switches from "no contact with the saw blade" to "contact with the saw blade", i.e. the actuation latency of the entire emergency brake unit 26, can be determined.

[0106] The third state sensor 56c can also comprise an electrical current sensor. If a current value detected in this way is compared with a bias element threshold value S3 stored in the memory unit 60, a conductivity of the bias element 42 can be determined.

[0107] Furthermore, the third state sensor 56c includes a force sensor. In this way, a preload force of the preload element 42 can be detected.

[0108] The monitoring unit 50 is further equipped with a user interface 64, which is signal-coupled to the computing unit 58. Each of the energy storage unit status parameter Z1, the actuating element status parameter Z2, and the preload element status parameter Z3 can be provided to a user of the tool 10 via the user interface 64. Optionally, the energy storage unit threshold value S1, the actuating element threshold value S2, and the preload element threshold value S3 can also be provided to the user. In the present example, the user interface 64 is designed as a display.

[0109] The monitoring unit 50 also includes a warning unit 66, which is also signal-coupled to the processing unit 58. A warning signal can be output by means of the warning unit 66. In this case, the warning unit 66 is embodied as a loudspeaker. It should be understood, however, that this is merely an example.

[0110] Alternatively, the warning unit 66 and the user interface 64 can be formed by a common display. In this example, the warning unit 66 is configured to output visual warning signals.

[0111] The actuator 34 can be operated using a method for operating an actuator of an emergency brake unit for a motor-driven tool. Within the scope of the method, the energy storage unit state parameter ZI, which characterizes a state of the energy storage unit 52, is recorded.

[0112] In addition, the actuating element state parameter Z2 is recorded, which characterizes a state of the actuating element 36.

[0113] Furthermore, the prestressing element state parameter Z3 is detected, which characterizes a state of the prestressing element 42.

[0114] Subsequently, an energy storage unit threshold value S1 associated with the energy storage unit state parameter ZI, a state parameter threshold value S2 associated with the actuating element state parameter Z2, and a prestressing element threshold value S3 associated with the prestressing element state parameter Z3 are obtained from the storage unit 60.

[0115] In addition, by means of the computing unit 58, the energy storage unit state parameter ZI is compared with the energy storage unit threshold value S1, the actuating element state parameter Z2 is compared with the actuating element threshold value S2 and the preload element state parameter Z3 is compared with the preload element threshold value S3.

[0116] The energy storage unit threshold value Sl is therefore assigned to the energy storage unit state parameter ZI, the actuating element threshold value S2 is assigned to the actuating element state parameter Z2 and the threshold value S3 is assigned to the state parameter S3.

[0117] The energy storage unit threshold value S1 limits a standard range of the energy storage unit state parameter ZI, the actuating element threshold value S2 limits a standard range of the actuating element state parameter Z2, and the preload element threshold value S3 limits a standard range of the preload element state parameter Z3. For reliable operation of the emergency brake unit 26, each of the energy storage unit state parameter ZI, the actuating element state parameter Z2, and the preload element state parameter Z3 must be within the respective assigned standard range.

[0118] Accordingly, the method triggers a blocking signal if one of the energy storage unit status parameter ZI, the actuating element status parameter Z2, and the preload element status parameter Z3 is outside the normal range. In this case, the emergency brake unit 26 cannot be operated.

[0119] In the event that one of the energy storage unit status parameter ZI, the actuating element status parameter Z2, and the preload element status parameter Z3 is within the standard range but also within an associated warning range, the method provides for issuing a warning signal by means of the warning unit 66. The warning range is selected within the respectively assigned standard range such that an energy storage unit status parameter ZI, the actuating element status parameter Z2, and / or the preload element status parameter Z3 lying within the warning range indicates an imminent loss of reliability.

[0120] In addition, within the scope of the method, the determined energy storage unit state parameter ZI, the determined actuating element state parameter Z2 and the determined preload element state parameter Z3 are provided to the user of the tool 10 by means of the user interface 64.

[0121] The energy storage unit threshold value S1, the actuating element threshold value S2 and the preload element threshold value S3 are also provided to the user of the tool 10 via the user interface 64.

[0122] As already explained in connection with the monitoring unit 50, the energy storage unit state parameter ZI, which characterizes a state of the energy storage unit 52, can be a number of actuation processes of the energy storage unit 52 that have already occurred and / or a storage capacity of the energy storage unit 52. The energy storage unit threshold value S1 accordingly describes a maximum number of permissible actuation processes and / or a permissible minimum storage capacity.

[0123] As already explained in connection with the monitoring unit 50, the actuating element state parameter Z2, which characterizes a state of the actuating element 36, can be a number of previously performed actuation processes of the actuating element 36, a position of the actuating element 36, an electrical resistance of the actuating element 36, an actuation latency of the actuating element 36, a voltage drop across the actuating element 36, and / or an actuation force of the actuating element 36. Accordingly, the actuating element threshold value S2 describes a number of maximum permissible actuation processes, a target position, a maximum permissible electrical resistance, a maximum permissible actuation latency, a maximum permissible voltage drop, and / or a minimum required actuation force of the actuating element 36.

[0124] As already explained in connection with the monitoring unit 50, the prestressing element state parameter Z3, which characterizes a state of the prestressing element 42, can be a conductivity of the prestressing element 42 and / or a prestressing force of the prestressing element 42. The prestressing element threshold value S3 accordingly describes a minimum permissible conductivity and / or a minimum permissible prestressing force.

[0125] In the present example, the method is executed as part of a test routine that always runs when the tool 10 is switched on. During the test routine, the energy storage unit state parameter ZI characterizing the state of the energy storage unit 52, the actuating element state parameter Z2 characterizing the actuating element 36, and the pre-tensioning element state parameter Z3 characterizing the pre-tensioning element 42 are recorded. The emergency brake unit 26 can only be operated if all of the energy storage unit state parameter ZI, the actuating element state parameter Z2, and the pre-tensioning element state parameter Z3 are within the respective assigned standard range.

[0126] In the example explained above, the monitoring unit 50 comprises a plurality of state sensors. Accordingly, a plurality of state parameters can be detected. It is understood that the monitoring unit 50 can also contain only a selection comprising one or more of the sensors explained above. Accordingly, only one or more of the state parameters explained above can be monitored. The method for operating the actuator can thus also be carried out with only a selection of state parameters comprising one or more state parameters.

[0127] The above explanations relate to a sawing device 10 in the form of a cross-cut saw. However, it is understood that the design as a cross-cut saw is only an example, and the above statements also apply to sawing devices of other designs, e.g., band saws.

[0128] List of reference symbols

[0129] 10 Tool 12 Sawing device 14 Base part 16 Support surface 18 Workpiece 20 Swivel device

[0130] 20a first section 20b second section 22 saw blade 24 handle 26 emergency brake unit 28 brake calliper

[0131] 30 Pressure element 32 Brake cam

[0132] 34 Actuator 36 Actuating element 36a first end 36b second end 38 Shape memory alloy 40 Slide

[0133] 42 Preload element 44 Actuating pin 46 Lifting magnet 48 Plunger 50 Monitoring unit

[0134] 52 electrical energy storage unit 54 electrical switching element 55 trigger control unit 56a first state sensor 56b second state sensor 56c third state sensor

[0135] 58 Computing unit 60 Storage unit

[0136] 62 Communication interface 64 User interface

[0137] 66 Warning unit SI Energy storage unit threshold S2 Actuator threshold S3 Preload element threshold Z1 Energy storage unit state parameter Z2 Actuator state parameter Z3 Preload element state parameter

[0138] Z4 Trip control unit status parameters

Claims

Patent claims 1. A method for operating an emergency brake unit (26) for a motor-driven tool (10), wherein the emergency brake unit (26) has an actuator (34) with an actuating element (36) and at least one electrical energy storage unit (52) which is electrically coupled to the actuating element (36) via an electrical switching element (54), so that the actuating element (36) can be selectively supplied with electrical energy stored in the energy storage unit (52) by actuating the switching element (54), the method comprising: - detecting an energy storage unit state parameter (ZI) that characterizes a state of the energy storage unit (52) and / or an actuating element state parameter (Z2) that characterizes a state of the actuating element (36), - comparing the detected energy storage unit state parameter (ZI) with an energy storage unit threshold value (S1) that limits a standard range assigned to the energy storage unit state parameter (ZI), and / or comparing the detected actuating element state parameter (Z2) with an actuating element threshold value (S2) that limits a standard range assigned to the actuating element state parameter (Z2), - triggering a blocking signal if at least one of the detected energy storage unit state parameter (ZI) and the detected actuating element state parameter (Z2) lies outside the respectively assigned standard range.

2. The method of claim 1, wherein the actuator (34) comprises a biasing element (42) and wherein the method comprises: - detecting a prestressing element state parameter (Z3) which characterizes a state of the prestressing element (42), - comparing the pre-stress element state parameter (Z3) with a pre-stress element threshold value (S3) which limits a standard range assigned to the pre-stress element state parameter (Z3), - Triggering a blocking signal when the bias element status parameter (Z3) is outside the normal range.

3. The method according to claim 2, wherein the bias element state parameter (Z3) describes a conductivity of the bias element (42) and the bias element threshold value (S3) describes a minimum permissible conductivity.

4. Method according to one of the preceding claims, wherein the energy storage unit state parameter (ZI) describes a number of actuation processes of the energy storage unit (52) that have already taken place and the energy storage unit threshold value (S1) describes a number of maximum permissible actuation processes and / or wherein the actuation element state parameter (Z2) describes a number of actuation processes of the actuation element (36) that have already taken place and the actuation element threshold value (S2) describes a number of maximum permissible actuation processes.

5. Method according to one of the preceding claims, wherein the actuating element state parameter (Z2) describes a position or a position difference of the actuating element (36) and the actuating element threshold value (S2) describes a desired position or a desired position difference.

6. Method according to one of the preceding claims, wherein the actuating element state parameter (Z2) describes an electrical resistance of the actuating element (36) and the actuating element threshold value (S2) describes a maximum permissible electrical resistance.

7. Method according to one of the preceding claims, wherein the actuating element state parameter (Z2) describes an actuation latency of the actuating element (36) and the actuating element threshold value (S2) describes a maximum permissible actuation latency.

8. Method according to one of the preceding claims, wherein the actuating element state parameter (Z2) describes a voltage drop across the actuating element (36) and the actuating element threshold value (S2) describes a maximum permissible voltage drop.

9. Method according to one of the preceding claims, wherein the actuating element state parameter (Z2) describes an actuating force of the actuating element (36) and the actuating element threshold value (S2) describes a minimum permissible actuating force and / or wherein the prestressing element state parameter (Z3) describes a prestressing force of the prestressing element (42) and the prestressing element threshold value (S3) describes a minimum permissible prestressing force.

10. The method according to any one of the preceding claims, wherein the energy storage unit state parameter (S1) describes a storage capacity of the energy storage unit (52) and the energy storage unit threshold value (S1) describes a permissible minimum storage capacity.

11. Method according to one of the preceding claims, wherein at least one of the energy storage unit state parameter (ZI), the actuating element state parameter (Z2) and the biasing element state parameter (Z3) is detected during a test routine.

12. The method according to any one of the preceding claims, further comprising providing at least one of energy storage unit state parameter (ZI), actuator state parameter (Z2) and biasing element state parameter (Z3) to a user.

13. The method according to any one of the preceding claims, further comprising triggering a warning signal if at least one of the energy storage unit state parameter (ZI), the actuating element state parameter (Z2) and the biasing element state parameter (Z3) is within the respectively assigned standard range and within an assigned warning range. Monitoring unit (50) for monitoring a state of an emergency brake unit (26) for a motor-driven tool (10), wherein the emergency brake unit (26) has an actuator (34) with an actuating element (36) and at least one electrical energy storage unit (52) which is electrically coupled to the actuating element (36) via an electrical switching element (54), so that the actuating element (36) can be selectively supplied with electrical energy stored in the energy storage unit (52) by actuating the switching element (54), with - at least one state sensor (56a, 56b) which is designed to detect an energy storage unit state parameter (ZI) which characterizes a state of the energy storage unit (52) and / or to detect an actuating element state parameter (Z2) which characterizes a state of the actuating element (36), - a storage unit (60) on which at least one of an energy storage unit threshold value (S1) and an actuating element threshold value (S2) is stored, which limits a respectively assigned standard range, - a computing unit (58) which is designed to compare the energy storage unit state parameter (ZI) detected by means of the state sensor (56a, 56b) with the energy storage unit threshold value (S1) and / or to compare the detected actuating element state parameter (Z2) with the actuating element threshold value (S2), and - a communication interface (62) for triggering a blocking signal. Emergency brake unit (26) for a motor-driven tool (10) with a monitoring unit (50) according to claim 14.

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