Method for changing an operating state of a machine tool, and machine tool

Abstract

The present invention relates to various methods for changing an operating state of a machine tool. In the methods according to the invention, a machine tool comprises an acceleration sensor, wherein the acceleration of the machine tool can be measured in the three spatial directions by means of the acceleration sensor. On the basis of these values, an overall acceleration can be ascertained, which can be compared with a threshold value a_drop. The machine tool can, for example, be switched off, or the operating state thereof can be changed, when the overall acceleration falls below the threshold value a_drop for longer than a time period t_drop. According to an alternative method for changing an operating state of a machine tool, the machine tool can be switched off, or the operating state thereof can be changed, when the overall acceleration falls below the threshold value a_drop for longer than a time period t_min_drop_impact and exceeds a second threshold value a_impact within a time period t_post_drop_impact. A second aspect of the invention relates to a machine tool for carrying out one of the methods for changing an operating state of the machine tool.

Description

[0001] METHOD FOR CHANGING AN OPERATING STATE OF A MACHINE TOOL AND MACHINE TOOL

[0002] The present invention relates to various methods for changing an operating state of a machine tool. In the methods according to the invention, a machine tool has an acceleration sensor, which can detect the acceleration of the machine tool in three spatial directions. Based on these values, a total acceleration can be determined, which can be compared with a threshold value a_drop. The machine tool can, for example, be shut down or change an operating state if the total acceleration falls below the threshold value a_drop for longer than a period of time t_drop.According to an alternative method for changing an operating state of a machine tool, the machine tool can be shut down or change an operating state if the total acceleration falls below the threshold value a_drop for longer than a time period t_min_drop_impact and exceeds a second threshold value a_mpact within a time period t_post_drop_impact. In a second aspect, the invention relates to a machine tool for carrying out one of the methods for changing an operating state of the machine tool.

[0003] Background of the invention:

[0004] Machine tools typically have switching devices for turning the machine tool on or off. Such switching devices or switches for machine tools can be designed, for example, as actuating switches or switching devices with a latching function. With actuating switches, the actuating switch must be actuated by a user at all times during operation to ensure the machine tool's operation. If such a device is dropped, it automatically shuts down due to the lack of actuation. In this way, the safety risk that can arise from such a falling machine tool can be significantly reduced.

[0005] For machine tools equipped with a switching device with a latching function, such an automatic and independent shutdown cannot be achieved in this way, since the device remains active even if the device falls, and the tool of the machine tool remains in motion, usually rotating. Various methods are known in the prior art for shutting down, braking, or otherwise changing the operating state of such machine tools with a switching device with a latching function in the event of a fall.

[0006] For example, it is known in the prior art to provide sensors in the handle area of ​​the machine tool which can detect whether the device is being held by the user or not. The machine tool can only be operated if the - usually capacitive - sensors detect that the device is being actively operated by a user, i.e. if the user is holding the machine tool securely and contact between the machine tool and the sensors in the handle of the machine tool is detected. Such sensors are often based on capacitance measurements and have the disadvantage that the user's hand must be positioned very precisely over the corresponding sensors on the handle of the machine tool in order to be detected. In addition, contamination or wearing a glove can make it difficult to detect the user's hand.Furthermore, it has been shown that the integration of sensors in the often space-limited handle of the machine tool can be very complex and cumbersome.

[0007] The object underlying the present invention is to overcome the above-described deficiencies and disadvantages of the prior art and to provide a method for changing the operating state of a machine tool, with which hazardous situations can be reliably detected and, for example, the machine tool can be shut down quickly and safely. Experts would appreciate it if the solution to be provided could be implemented in the machine tool in a particularly simple, straightforward, and inexpensive manner. Furthermore, within the context of the invention, a machine tool for carrying out the method is to be provided.

[0008] The problem is solved by the subject matter of the independent claims. Advantageous embodiments of the subject matter of the independent claims can be found in the dependent claims.

[0009] Description of the invention:

[0010] According to the invention, a method for changing an operating state of a machine tool is provided. The method for changing an operating state of a machine tool is characterized by the following method steps: a) providing a machine tool with an acceleration sensor, b) detecting an acceleration of the machine tool in the three spatial directions, thereby obtaining the acceleration values ​​x, y, and z, c) determining a total acceleration of the machine tool based on the acceleration values ​​x, y, and z, d) comparing the total acceleration with a threshold value a_drop, e) changing an operating state of the machine tool if the total acceleration falls below the threshold value a_drop for longer than a time period t_drop.

[0011] Advantageously, this method can be used to detect fall heights of 45 cm and above with particular reliability. The method for changing an operating state of the machine tool can, for example, be a method for switching the machine tool off if a dangerous situation is detected. The dangerous situation can, for example, consist of the machine tool falling to the ground, which can obviously endanger the user or bystanders during operation. In addition to switching off the machine tool, a change in an operating state of the machine tool can also consist of the machine tool or its tool being braked, so that, for example, the motor of the machine tool rotates at a lower rpm or speed or the tool of the machine tool rotates more slowly.In addition, if the operating state of the machine tool changes, another operating mode can also be switched on.

[0012] The change in the operating state of the machine tool or the shutdown of the machine tool can advantageously be performed while still in the air, thus preventing injury to the machine tool user with particular reliability. This first embodiment of the invention is also preferably referred to as "drop detection" within the meaning of the invention.

[0013] In the following, the invention is generally explained using the example of shutting down a machine tool. In this exemplary embodiment, the invention relates to a method for shutting down a machine tool, wherein the machine tool can be shut down if the total acceleration falls below the threshold value a_drop for longer than a period of time t_drop.

[0014] The invention eliminates the need for a capacitive sensor in the handle or the complex integration of sensors in the machine tool housing. This advantageously allows the machine tool's electronics to be kept simple, resulting in a particularly compact and manageable machine tool. By implementing a method for changing the operating state of a machine tool in software, a surprisingly high degree of reliable shutdowns can be achieved in safety-relevant cases.

[0015] In the context of the present invention, a machine tool with at least one acceleration sensor is provided. Many machine tools already have acceleration sensors, so that in the context of the present invention, in particular acceleration data that is "already" collected and is therefore available is evaluated. This often already available data is subjected to additional utilization in the context of the present invention by being used as the basis for automatic and independent shutdown of the machine tool. In the context of the present invention, advantageously, no additional effort is required to acquire data; rather, data that is often "already" available is utilized even better by this data contributing to defining shutdown conditions for the machine tool.

[0016] It is preferred in the sense of the invention that in a rest position of the machine tool the acceleration due to gravity of g = 9.81 m / s 2 can be measured. The values ​​for the acceleration due to gravity in the three spatial directions x, y and z can be determined, for example, as follows: a_x = 0, a_y = 0 and a_z = g = 9.81 m / s 2. It may also be preferred within the meaning of the invention that an offset is applied to the determined values ​​in order to normalize all three acceleration values ​​to a value of "zero". It is preferred within the meaning of the invention that the further evaluation of the data is carried out depending on the method used to determine the acceleration due to gravity in the three spatial directions. Depending on whether an offset is applied to the values, the determination of the total acceleration or the underlying calculations to determine the conditions for shutting down the machine tool may change. Whether an offset is used to normalize the acceleration values ​​x, y and z to a uniform value, for example 0 m / s 2 , or whether one of the acceleration values, for example the acceleration value z, is to be normalized with the value of the acceleration due to gravity g = 9.81 m / s 2can, for example, also depend on the type of sensor used in the machine tool to determine the acceleration values ​​x, y and z.

[0017] In the context of the present invention, acceleration data or values ​​are collected in the three spatial directions. Those skilled in the art recognize the three spatial directions as the axes of a three-dimensional Cartesian coordinate system. For the purposes of the invention and to keep the terminology simple, the acceleration values ​​are referred to as "x," "y," and "z," where the acceleration value x represents the acceleration a_x in the x-direction, the acceleration value y represents the acceleration a_y in the y-direction, and the acceleration value z represents the acceleration a_z in the z-direction.

[0018] In a second aspect, the invention relates to a machine tool for carrying out the proposed method for changing an operating state of the machine tool, wherein the machine tool comprises, in addition to the at least one acceleration sensor, a control device and / or a processor for evaluating the acceleration data or values. In other words, the machine tool has a control device and / or a processor designed to evaluate the acceleration data or values ​​determined by the at least one acceleration sensor. The control device and / or the processor of the machine tool are particularly designed to determine a total acceleration a of the machine tool based on the acceleration values ​​x, y and z in the three spatial directions.The total acceleration a of the machine tool is then compared with a threshold value a_drop, where the threshold value a_drop is preferably a predetermined threshold value.

[0019] The formulation that "the threshold value a_drop is preferably a predetermined threshold value" preferably means, within the meaning of the invention, that the threshold value a_drop cannot be set by a user of the machine tool, but is specified, for example, by the manufacturer of the machine tool. For example, the threshold value a_drop can be stored in a memory in the control device or in the machine tool. Look-up tables or the like can be used for this purpose. It can also be preferred within the meaning of the invention for data, such as threshold values, to be subsequently uploaded to the machine tool as part of a maintenance or overhaul process. In this way, for example, changes to the threshold values ​​can be transmitted to the machine tool and new threshold values ​​can be uploaded to the machine tool.

[0020] In the context of the present invention, an operating state of the machine tool is changed when the total acceleration of the machine tool falls below the threshold value a_drop for longer than a time period t_drop. Preferably, the machine tool can be shut down, in particular, when the total acceleration falls below the threshold value a_drop for longer than a time period t_drop.

[0021] In the sense of the invention, the drop in the overall acceleration is preferably interpreted as the machine tool falling down, so that the machine tool can be switched off when a fall of the machine tool is detected. In the context of the embodiment of the invention described here, the fall of the machine tool is assumed in particular when the overall acceleration falls below the threshold value a_drop for longer than a time period t_drop, wherein the time period t_drop preferably also represents a predetermined time period. The time period t_drop can, for example, be in the range from 0.1 to 1 second (s). The threshold value a_drop can, for example, be between 5 and 60% of the initial value for the overall acceleration of the machine tool, wherein the initial value of the overall acceleration is determined in particular during normal operation of the machine tool.

[0022] By switching off the machine tool or changing its operating state through clever evaluation and processing of three-dimensional acceleration data, the invention can provide a significant electronic safety function, allowing fall situations of the machine tool to be detected particularly reliably. If a machine tool is detected as having fallen, the machine tool or its tool can be brought to a rapid stop, thus minimizing safety risks for the user. It has been shown that the invention can detect particularly early whether a machine tool is about to fall during operation. Based on this rapid detection, the machine tool can be switched off in the event of a fall, thus avoiding dangerous situations.According to the drop protection embodiment of the invention, the proposed electronic safety function is characterized in that a shutdown of the machine tool or a change in the operating state of the machine tool occurs when the total acceleration falls below the threshold value a_drop and this falling below the threshold value a_drop lasts longer than a time period t_drop. The machine tool can preferably be shut down when the end of the time period t_drop is reached, i.e., when the end of the time period t_drop is reached and the total acceleration a is still below the threshold value a_drop. Alternatively, an operating state of the machine tool can be changed when the end of the time period t_drop is reached and the total acceleration a is still below the threshold value a_drop.

[0023] According to the invention, it is preferred that the acceleration data determined with the acceleration sensor are filtered before further processing, i.e., in particular before calculating the total acceleration a. According to the invention, it is preferred that the time period t_drop has a start time t_drop_start and a stop time t_drop_stop. In other words, the time period t_drop begins with the start time t_drop_start and the time period t_drop ends with the stop time t_drop_stop. According to the invention, this preferably means that the times t_drop_start and t_drop_stop limit the time period t_drop and represent the start and end times of the time period t_drop. According to the drop protection embodiment of the invention, the machine tool is switched off when the stop time t_drop_stop is reached.

[0024] According to the invention, it is preferred that a time point t_drop_start is recorded and a time recording is started when the total acceleration a falls below the threshold value a_drop. In other words, a time recording can begin when the total acceleration a falls below the threshold value a_drop. In still other words, the start time of a predetermined time period t_drop is recorded, wherein the start time t_drop_start is characterized by the total acceleration a falling below the threshold value a_drop. The shutdown of the machine tool or a change in an operating state of the machine tool preferably occurs at the stop time t_drop_stop of the time period t_drop, i.e., at its end.

[0025] In a second embodiment of the invention, an alternative method for changing an operating state of a machine tool is presented, wherein the alternative method is characterized by the following method steps: a) providing a machine tool with an acceleration sensor, b) detecting an acceleration of the machine tool in the three spatial directions, whereby the acceleration values ​​x, y and z are obtained, c) determining the total acceleration, d) comparing the total acceleration with a first threshold value a_drop, e) changing an operating state of the machine tool if the total acceleration falls below the threshold value a_drop for longer than a time period t_min_drop_impact and the total acceleration exceeds a second threshold value a_mpact within a time period t_post_drop_impact.

[0026] In this embodiment of the invention, it is provided that the machine tool is switched off or changes an operating state when the total acceleration falls below the threshold value a_drop for longer than a time period t_min_drop_impact and the total acceleration exceeds a second threshold value ajmpact within a time period t_post_drop_impact.

[0027] In this embodiment of the invention, the total acceleration initially falls below the first threshold a_drop, whereby the total acceleration in this scenario does not fall below the first threshold a_drop long enough to cause the machine tool to shut down or change an operating state of the machine tool. The total acceleration remains below the first threshold a_drop for longer than a time period t_min_drop_impact. The time period t_min_drop_impact can, for example, be in the range of 0.05 to 0.5 s. The time period t_min_drop_impact is preferably significantly shorter than the time period t_drop in the first embodiment of the invention.

[0028] If the total acceleration increases again after the time period t_min_drop_impact has elapsed and in particular exceeds the first threshold value a_drop, a new time period starts, which in the context of the invention is referred to as t_post_drop_impact. The increase in the total acceleration is preferably interpreted in the context of the invention as the machine tool being caught by the user or as the machine tool hitting a floor or a subsurface. The total acceleration therefore preferably increases when the machine tool is caught or hits a floor. In order to ensure safe shutdown in this situation too, the machine tool in this second embodiment of the invention can be switched off or change an operating state if the total acceleration exceeds the second threshold value a_mpact within this time period t_post_drop_impact. It is preferred in the sense of the invention that the renewed orA rapid increase in the total acceleration after the expiry of the time period t_min_drop_impact is interpreted as a fall or impact of the machine tool. The second embodiment of the invention described here is preferably also referred to as “drop & impact detection” within the meaning of the invention, because the rapid increase in the total acceleration and the associated exceeding of the second threshold value ajmpact advantageously ensure that the device is safely switched off in the event of a sudden braking of the device, for example due to an impact of the device. It can also be preferred within the meaning of the invention that the rapid increase in the total acceleration and the associated exceeding of the second threshold value ajmpact is used as a starting point for changing an operating mode of the machine tool.For example, the machine tool, its tool and / or its motor can be braked if a rapid increase in the overall acceleration and an exceedance of the second threshold ajmpact is detected.

[0029] A significant advantage of the invention is that the proposed methods for changing the operating state of a machine tool can be particularly easily integrated and implemented into existing software packages. The software or the proposed methods can be operated, for example, in a control device or a processor of a machine tool. Due to the simple structure of the method, only a low CPU load of the control device and / or the processor of the machine tool is required for implementation.

[0030] According to the invention, it is preferred that the first threshold a_drop is smaller than the second threshold a_mpact. While the first threshold a_drop is, for example, in a range of 5 to 60% of an initial value of the total acceleration, the second threshold a_mpact can be, for example, 150% of the initial value of the total acceleration. According to the invention, it is preferred that the second threshold a_mpact is in a range of 100 to 500% of the initial value of the total acceleration, and very particularly preferably in a range of 150 to 300% of the initial value of the total acceleration.

[0031] According to the invention, it is preferred that the time period t_post_drop_impact starts when the total acceleration exceeds the first threshold value a_drop. Furthermore, according to the invention, it is preferred that the time period t_min_drop_impact be a predetermined time period.

[0032] It is preferred in the sense of the invention that the time period t_min_dropjmpact is shorter than the time period t_drop, so that the alternative method for changing an operating state of a machine tool is used when the total acceleration does not fall below the first threshold value a_drop for long enough because an increase in the total acceleration is detected beforehand.

[0033] In a second aspect, the invention relates to a machine tool for carrying out the proposed methods. The terms, definitions, and technical advantages introduced for the methods for changing an operating state of a machine tool preferably apply analogously to the machine tool. The machine tool comprises an acceleration sensor for detecting acceleration data and a control device for evaluating the acceleration data detected by the acceleration sensor. Within the meaning of the invention, it is preferred that the acceleration data x, y, and z are detected in the three spatial directions, wherein a total acceleration can be determined based on the acceleration data in the three spatial directions. The machine tool can preferably be switched off if the total acceleration falls below a threshold value a_drop for longer than a time period t_drop.

[0034] It is preferred in the sense of the invention that the machine tool is switched off or changes its operating state when the total acceleration falls below a threshold value a_drop for longer than a time period t_min_drop_impact and the total acceleration exceeds a second threshold value ajmpact within a time period t_post_drop_impact.

[0035] According to the invention, a decrease in the overall acceleration is preferably interpreted as the machine tool falling. Depending on the sensor type used to determine the acceleration values ​​x, y, and z, it may also be preferable for an increase in the overall acceleration to be interpreted as the machine tool falling.

[0036] When using an appropriate sensor type, the total acceleration during normal machine tool operation can be zero or close to zero. If the machine tool falls, the total acceleration in at least one of the spatial directions can increase to a value other than zero, for example, to 9.81 m / s. 2 , which corresponds to the acceleration due to gravity. Particularly in the "drop & impact detection" embodiment of the invention, the total acceleration can subsequently decrease again, for example, to a value close to zero, before rapidly increasing. The machine tool can, for example, be switched off or its motor or tool decelerated if the total acceleration exceeds the second threshold value ajmpact.

[0037] In this other embodiment of the invention, which may arise, for example, due to a different sensor type for determining the acceleration values ​​x, y, and z, the machine tool can, for example, be shut down or change its operating mode if the total acceleration exceeds a threshold value a_drop for longer than a time period t_drop. In the "drop & impact detection" embodiment of the invention, the machine tool can be shut down or change its operating state if the total acceleration exceeds a threshold value a_drop for longer than a time period t_min_dr°p_impact and the total acceleration exceeds a second threshold value ajmpact within a time period t_post_drop_impact.

[0038] Further advantages emerge from the following description of the figures. The figures, the description, and the claims contain numerous features in combination. The skilled person will also expediently consider the features individually and combine them into further meaningful combinations. They show:

[0039] Fig. 1 exemplary temporal course of the total acceleration during a drop detection according to the first embodiment of the invention («drop detection»)

[0040] Fig. 2 Example of a temporal progression of the total acceleration during a drop-impact detection according to the second embodiment of the invention («drop & impact detection»)

[0041] Implementation examples and figure descriptions:

[0042] Figure 1 shows an exemplary temporal progression of the total acceleration during a drop detection according to the first embodiment of the invention. The total acceleration is plotted on the y-axis of the graph shown in Figure 1, with the total acceleration preferably being expressed in meters (seconds). 2 or m / s 2 The x-axis represents time in seconds (s). During normal operation of the machine tool, the total acceleration is approximately 10 m / s. 2 If the machine tool falls to the ground during operation, this is noticeable in the temporal progression of the total acceleration as a rapid drop in the total acceleration. The total acceleration can drop to a value of approximately 0 m / s during a fall. 2drop. If the total acceleration falls below the predefined threshold value a_drop, the time period t_drop begins to run, at the end of which the machine tool is switched off or the machine tool changes an operating state, for example by braking the machine tool, its tool and / or its motor. The switching off of the machine tool as an example of a change in the operating state of the machine tool is marked by a black dot in Figures 1 and 2. In the example shown in Figure 1, the threshold value a_drop is approximately 60% of the original starting value of the total acceleration. Other values ​​for the threshold value a_drop are of course also conceivable. In the exemplary embodiment of the first embodiment of the invention shown in Figure 1, the time period t_drop is approximately 0.3 s.

[0043] Figure 2 shows an exemplary temporal progression of the total acceleration during a drop and impact detection according to the first embodiment of the invention ("drop & impact detection"). In the plot shown in Figure 2, the same quantities are total acceleration in the unit m / s. 2 and time in seconds (s). In addition to the first threshold a_drop, Figure 2 also shows the time periods t_min_drop_impact and t_post_drop_impact, as well as the second threshold ajmpact. In the exemplary embodiment of the second refinement of the invention shown in Figure 2, the second threshold ajmpact is significantly greater than the first threshold a_drop.

[0044] The total acceleration initially decreases due to the falling of the machine tool and takes, for example, a value of approximately 0 m / s 2During this drop in the total acceleration, the total acceleration falls below the first threshold value a_drop, whereby the first time period t_min_drop_impact begins. The time period t_min_drop_impact is preferably shorter than the time period t_drop of the first embodiment of the invention and is, for example, 0.15 s. If, after the end of the time period t_min_drop_impact, the total acceleration is still below the first a_drop and then increases again - for example, because the machine tool impacts a surface - a second time period t_post_drop_impact begins. The second time period t_post_drop_impact preferably begins when the total acceleration - coming from low values ​​- exceeds the first threshold value a_drop.The impact or impact of the machine tool preferably leads to a very rapid increase in the total acceleration, so that the total acceleration intersects and exceeds the second, higher threshold value ajmpact after a short time. At this point in time, according to the second embodiment of the invention, the machine tool is shut down or an operating state is changed, with a shutdown time in this second embodiment of the invention preferably lying within the second time period t_post_drop_impact. In Figure 2, the shutdown of the machine tool or a change in the operating state of the machine tool, such as deceleration, is also marked by a black dot.

Claims

Patent claims 1 . Method for changing an operating state of a machine tool, the method being characterized by the following method steps: a) providing a machine tool with an acceleration sensor, b) detecting an acceleration of the machine tool in the three spatial directions, whereby the acceleration values ​​x, y and z are obtained, c) determining a total acceleration of the machine tool based on the acceleration values ​​x, y and z, d) comparing the total acceleration with a threshold value a_drop, e) changing an operating state of the machine tool if the total acceleration falls below the threshold value a_drop for longer than a time period t_drop.

2. Method according to claim 1, characterized in that the decrease in the total acceleration is interpreted as the machine tool falling down.

3. Method according to claim 1 or 2, characterized in that the total acceleration for the time period t_drop drops to values ​​of less than 25% of an original starting value of the total acceleration.

4. Method according to one of the preceding claims, characterized in that the time period t_drop is in a range of 0.1 to 1 s.

5. Alternative method for changing an operating state of a machine tool, the method being characterized by the following method steps: a) Providing a machine tool with an acceleration sensor, b) Detecting an acceleration of the machine tool in the three spatial directions, whereby the acceleration values ​​x, y and z are obtained, c) Determining a total acceleration of the machine tool based on the Acceleration values ​​x, y and z, d) comparing the total acceleration with a first threshold value a_drop, e) changing an operating state of the machine tool if the total acceleration falls below the threshold value a_drop for longer than a time period t_min_drop_impact and the total acceleration exceeds a second threshold value a_mpact within a time period t_post_drop_impact. Method according to claim 5, characterized in that the first threshold value a_drop is smaller than the second threshold value a_mpact. Method according to claim 5 or 6, characterized in that the time period t_post_dropjmpact starts when the total acceleration exceeds the first threshold value a_drop. Method according to one of claims 5 to 7, characterized in that the time period t_min_dropjmpact is a predetermined time period.Method according to one of claims 5 to 8, characterized in that the renewed increase in the total acceleration after the expiration of the time period t_min_dropjmpact is interpreted as a catch or impact of the machine tool. Method according to one of the preceding claims, characterized in that the time period t_min_dropjmpact is shorter than the time period t_drop, so that the alternative method for changing an operating state of a machine tool is used when the total acceleration does not fall below the first threshold value a_drop for long enough because an increase in the total acceleration is detected beforehand. A machine tool for carrying out the method according to one of the preceding claims, wherein the machine tool comprises an acceleration sensor for detecting acceleration data and a control device for evaluating the acceleration data detected by the acceleration sensor. The machine tool according to claim 11, characterized in that the acceleration data x, y, and z are detected in the three spatial directions, wherein a total acceleration of the machine tool can be determined based on the acceleration data in the three spatial directions. The machine tool according to claim 11 or 12, characterized in that the machine tool can be switched off if the total acceleration falls below a threshold value a_drop for longer than a time period t_drop.Machine tool according to one of claims 11 to 13, characterized in that the machine tool can be switched off if the total acceleration falls below a threshold value a_drop for longer than a time period t_min_drop_impact and the total acceleration exceeds a second threshold value a_mpact within a time period t_post_drop_impact.

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