Method for braking a machine tool with at least two energy supply devices, and machine tool

Abstract

The present invention relates to a method for braking a machine tool, wherein the machine tool is a battery-powered machine tool and can be connected to at least a first energy supply device and a second energy supply device in order to be supplied with electrical energy. The electrical energy generated when the machine tool is braked is fed back into the first energy supply device and / or the second energy supply device of the machine tool. The energy supply devices are connected in series, and the method may comprise active regulation of an intermediate circuit voltage, in which a limit value of the intermediate circuit voltage (U_Zwischenkreis, Limit) is lower than a sum of the limit values of the voltages (U_Akkupack pack, limit) of the energy supply devices. The invention also relates to a machine tool for carrying out the braking method.

Description

[0001] METHOD FOR BRAKING A MACHINE TOOL WITH AT LEAST TWO POWER SUPPLY DEVICES AND MACHINE TOOL

[0002] The present invention relates to a method for braking a machine tool, wherein the machine tool is a battery-operated machine tool and is connectable to at least a first energy supply device and a second energy supply device in order to be supplied with electrical energy. The electrical energy released when the machine tool is braked is fed back into the first energy supply device and / or the second energy supply device of the machine tool. The energy supply devices are connected in series, and the method can comprise active control of an intermediate circuit voltage, in which a limit value of the intermediate circuit voltage U_Intermediate_Circuit,Limit is smaller than a sum of the limit values ​​of the voltages U_Battery_Pack,Limit of the energy supply devices. In a second aspect, the invention relates to a machine tool for carrying out the braking method.

[0003] Background of the invention:

[0004] Machine tools are known in the art that can be connected to more than one power supply device to supply them with electrical energy. These power supply devices are often connected in series to increase the system voltage or to handle applications with higher power requirements. In addition, the use of more than one power supply device can increase the range of the power supply devices or their running time. Machine tools should be brought to a quick stop. This can prevent the machine tool or its tool from running for a long time, which can lead to accidents or injuries to the machine tool user, especially during such a rundown.

[0005] The electrical energy released when a machine tool is braking can be fed back into the machine tool's power supply devices ("recuperation"). When feeding energy back, care must be taken to ensure that the power supply devices are not damaged by overload or similar. This can be particularly challenging if the machine tool comprises more than one power supply device, as, for example, occurring voltages and / or currents may be unevenly distributed among the existing power supply devices. Such asymmetric distributions can lead to situations in which the individual power supply devices are loaded so unevenly that recuperation or other properties of the machine tool are negatively affected.If, for example, a current and / or voltage limit is exceeded for one of the several energy supply devices, but another energy supply device is still operating significantly below such a current and / or voltage limit, one of the energy supply devices may be overloaded and thus exposed to the risk of damage, while the other energy supply device may not operate at its full potential, so that, for example, less electrical energy is fed back into the energy supply devices than would be technically possible.

[0006] The object underlying the present invention is to overcome the deficiencies and disadvantages of the prior art described above and to provide methods for braking a machine tool with two energy supply devices, as well as such a machine tool, with which on the one hand the most effective protection of a user of the machine tool is made possible, and on the other hand a machine tool with a particularly long running time or battery range can be provided, ie that electrical energy is fed back into the energy supply devices of the machine tool as efficiently as possible, in particular when the machine tool has two energy supply devices.

[0007] 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.

[0008] Description of the invention:

[0009] According to the invention, a method for braking a machine tool is provided, wherein the machine tool is a battery-operated machine tool and can be connected to at least a first energy supply device and a second energy supply device in order to be supplied with electrical energy. The electrical energy released when the machine tool is braked is fed back into the first energy supply device and / or the second energy supply device of the machine tool. The energy supply devices are connected in series, wherein a limit value of the intermediate circuit voltage U_Intermediate_Circuit, Limit is smaller than a sum of the limit values ​​of the voltages U_Battery_Pack, Limit of the energy supply devices. Within the meaning of the invention, it is preferred that the machine tool itself, its motor, or the tool of the machine tool can be braked using the proposed braking method.

[0010] The method advantageously makes it possible to feed the released braking energy back into the energy supply devices particularly efficiently. According to the invention, it is preferred that the machine tool be connectable to at least two energy supply devices for supplying electrical energy. The method can be described for a first and a second energy supply device, but is of course equally applicable to machine tools with three, four, five, six, seven, or more energy supply devices. These additional energy supply devices could be referred to as the "nth energy supply device" (see in particular the figures). For example, the machine tool can have receiving areas or options for coupling two or more energy supply devices.For the purposes of the invention, it is preferred that the terms accumulator ("accumulator"), battery, battery pack, and energy supply device be used synonymously. Likewise, for the purposes of the invention, it is preferred that the terms "limit" and "threshold" be used synonymously. For the purposes of the invention, it is preferred to refer to the control of the recuperation or braking process as method step S1.

[0011] Preferably, the limit value of the intermediate circuit voltage can be determined in such a way that even with a highly asymmetrical distribution of the voltage between the energy supply devices, the voltage limit value of each energy supply device of the machine tool is not exceeded. This can advantageously ensure that the intermediate circuit voltage does not exceed the limit value of the intermediate circuit voltage U_Intermediate_Circuit, Limit during recuperation. In this way, the voltage limit values ​​of the individual energy supply devices can then advantageously be adhered to. The invention can advantageously ensure that the permissible current and voltage limit values ​​are adhered to even in a machine tool system with several energy supply devices connected in series. For this purpose, the machine tool can have electronics orinclude motor electronics that controls recuperation in the various energy supply devices accordingly. Within the meaning of the invention, it is particularly preferred that a maximum recuperation current and a maximum battery pack voltage are not exceeded.

[0012] According to the invention, it is preferred that a voltage of the system comprising the machine tool and the energy supply devices is monitored. This monitoring can be ensured, for example, by the electronics or motor electronics of the machine tool. According to the invention, this voltage of the system comprising the machine tool and the energy supply devices can preferably be referred to as the “system voltage”. Furthermore, according to the invention, it is preferred to monitor an intermediate circuit voltage during recuperation in order not to exceed a permissible maximum voltage of the energy supply devices. With the invention, this can advantageously be ensured in that the limit value of the intermediate circuit voltage U_Intermediate circuit, Limit is smaller than the sum of the limit values ​​of the voltages U_Battery pack, Limit of the energy supply devices.This can, in particular, prevent the situation where the voltage limit for recuperation is already exceeded for one of the energy supply devices while the voltage for another energy supply device is still significantly below the limit. Tests have shown that the invention achieves particularly good results when the energy supply devices have different charge states, different temperatures, and therefore different internal resistances, so that the intermediate circuit voltage is distributed particularly asymmetrically among the voltages of the energy supply devices. In these cases, the invention can enable particularly efficient recuperation of electrical energy.

[0013] Within the meaning of the invention, it is particularly preferred to limit the recuperation current to smaller values ​​in order to keep the voltage increase during recuperation so low that the voltage of the energy supply devices does not exceed the corresponding current and voltage limit values ​​under all operating conditions of the machine tool. This can advantageously be achieved by making the limit value of the intermediate circuit voltage U_Intermediate Circuit, Limit smaller than the sum of the limit values ​​of the voltages U_Battery Pack, Limit of the energy supply devices. It has been shown that in this way, the greatest possible recuperation can be provided in a system with a machine tool and several energy supply devices connected in series. In particular, the invention enables active control of the intermediate circuit voltage, wherein this active control is preferably achieved by adapting the braking process of the machine tool.This advantageously ensures that the energy supply devices are operated within their power limits, but without exceeding the limit values ​​for current and / or voltage.

[0014] The invention particularly represents a method for recuperation in a series circuit of multiple power supply devices, wherein the method prevents exceeding a maximum permissible voltage of the series-connected power supply devices. The invention advantageously enables optimal recuperation in a series circuit of multiple power supply devices. A particular advantage of the invention is that the optimized recuperation also minimizes the braking time in which the machine tool or its tool can be brought to a standstill, thus making use of the machine tool particularly safe for the user.

[0015] In machine tools with a series connection of power supply devices, the power supply devices can acquire or exhibit different properties during operation of the machine tool or during the feeding back of electrical energy to the power supply devices. The power supply devices can differ, for example, in terms of their charge level, temperature, and / or internal resistance. The invention allows the feeding back of electrical energy to the power supply devices to be maximized, which advantageously simultaneously leads to the braking time for the machine tool being minimized. This is because a particularly short braking time offers particularly good protection for the user of the machine tool against injury.One advantage of the invention is that the limit values ​​of the series-connected power supply devices can be optimally utilized without exceeding the current and voltage limits of any individual power supply device within the series circuit. The invention enables active control of the intermediate circuit voltage by adjusting the braking process, so that the limit values ​​of the power supply devices are (almost) reached but not exceeded. The limit values ​​of the power supply devices are preferably the voltage and current limits.

[0016] According to the invention, it is preferred that the limit value of the intermediate circuit voltage U_Intermediate circuit, Limit is obtained by multiplying the limit value of the voltages U_Battery pack, Limit by a number n of energy supply devices and a factor k_Unbalance. The inventor has recognized that the asymmetrical distribution of the voltage between the different energy supply devices can be counteracted by introducing a so-called unbalance factor k_Unbalance, by which the series connection of the limit values ​​of the voltage U_Battery pack, Limit of the energy supply devices can be multiplied. In addition, the limit value of the voltage U_Battery pack, Limit of the energy supply devices is multiplied by the number n of energy supply devices in order to obtain the limit value of the intermediate circuit voltage U_Intermediate circuit, Limit.Within the meaning of the invention, it is preferred that the calculation of the imbalance factor is referred to as method step S2. When calculating the limit value of the intermediate circuit voltage U_Intermediate_Circuit,Limit as the product of the limit value of the voltages U_Battery_Pack,Limit, the number n of energy supply devices, and the factor k_Unbalance, it is assumed that the voltage limit values ​​of the energy supply devices used in a machine tool are equal or substantially equal. Therefore, the constant or substantially constant voltage limit value U_Battery_Pack,Limit can be multiplied by the number n of energy supply devices to obtain the sum of the limit values ​​of the voltages of the energy supply devices.If the limit values ​​of the voltages of the power supply devices are not the same for all power supply devices of the machine tool, the product of the number n of power supply devices and the limit value of the voltages U_Akkupack, Limit can be calculated by a sum. To obtain the limit value of the intermediate circuit voltage U_IntermediateCircuit,Limit, this sum can then be multiplied by the unbalance factor k_Unbalance.

[0017] According to the invention, it is preferred that the factor k_Unbalance lies between 0 and 1. In this case, the factor k_Unbalance can also assume the limit values ​​0 and 1, whereby a factor k_Unbalance with the value 1 according to the invention preferably means that there is no imbalance between the energy supply devices, i.e. no "unbalance". In this case, the energy supply devices of the machine tool all behave the same or essentially the same. Preferably, a high unbalance factor k_Unbalance, which lies in the range of 1, represents energy supply devices that behave very similarly, while a small unbalance factor k_Unbalance, which lies close to 0, represents a large inequality between the behavior of the individual energy supply devices of the machine tool.

[0018] It is preferred within the meaning of the invention that, within the scope of the proposed method, a limit value of a recuperation current l_Rekuperation,Limit is not exceeded. In this embodiment of the invention, active control of the recuperation current can be enabled by adapting the braking process, so that the limit values ​​of the energy supply devices are (almost) reached, but not exceeded. It is preferred within the meaning of the invention that the current in a series connection through all energy supply devices is the same or essentially the same, so that the limit value for the recuperation current can be ensured particularly easily for all energy supply devices. Advantageously, in this embodiment of the invention, not only the voltage limit values ​​of the energy supply devices are adhered to, but also the maximum permissible recuperation currents of the series-connected energy supply devices.Preferably, in a series connection, the current through the energy supply devices is the same or substantially the same, so that this constant or substantially constant current can be particularly easily monitored by the machine tool or its electronics for the maximum permissible recuperation current.

[0019] According to the invention, it is preferred that the limit value of a recuperation current l_Rekuperation,Limit corresponds to a minimum of the limit values ​​of the recuperation currents of the energy supply devices. According to the invention, this preferably means that the limit value of a recuperation current l_Rekuperation,Limit can be determined from the minimum of the recuperation current limit values ​​of the series-connected energy supply devices.

[0020] A possible calculation of the factor k_Unbalance for a series connection of two battery packs is explained in the following application example of the invention. The designations U_Akku, 1 and U_Akku, 2 preferably represent the voltages of the first and second energy supply devices measured during recuperation. If the voltage U_Akku, 1 measured at the first energy supply device is greater than the voltage U_Akku, 2 measured at the second energy supply device, the factor k_Unbalance can be calculated as follows:

[0021] In other cases, the factor k_Unbalance can be calculated as follows: By calculating the factor k_Unbalance differently, depending on how the voltages of the machine tool's power supply devices relate to each other, the factor k_Unbalance can advantageously be calculated for all possible states of the system consisting of the machine tool and power supply devices. For machine tools that are supplied with electrical energy by more than two power supply devices, the person skilled in the art can adapt the above case distinction and formula accordingly.

[0022] According to the invention, it is preferred that the voltage measurements and / or the update rate for calculating the factor k_Unbalance be performed with a period that is significantly shorter than the rise time of the recuperation current. This ensures that any asymmetrical voltage distribution between the energy supply devices is monitored sufficiently closely during the rise in recuperation. This can be achieved, in particular, by regularly determining the electrical parameters of the machine tool or the energy supply devices through measurements, so that the factor k_Unbalance can be calculated and adjusted if necessary at regular intervals.In particular, this allows for particularly rapid and flexible responses to changes in the operating parameters of the energy supply devices, such as charge state, temperature and / or internal resistance, in order to ensure the greatest possible feed-back of electrical energy into the energy supply devices.

[0023] In a second aspect, the invention relates to a machine tool for carrying out the proposed method. The terms, definitions, and technical advantages introduced for the braking method preferably apply analogously to the machine tool. The machine tool is preferably configured to brake the machine tool itself, its motor, or the tool of the machine tool. It is particularly preferred within the meaning of the invention that the tool of the machine tool is brought to a standstill or substantially to a standstill by the proposed braking method. Within the meaning of the invention, the phrase "substantially to a standstill" preferably means that a large portion of the kinetic rotational energy is removed from the tool, the motor, and / or the machine tool, so that the machine tool is braked.

[0024] The motor of the machine tool can preferably be a brushless motor, which can preferably deliver a power of more than 1.8 kilowatts (kW). The machine tool can preferably be a brushless electrical device with a braking function. For example, the machine tool can be designed as an electrically operated cut-off grinder. Within the meaning of the invention, it is particularly preferred that the machine tool is a battery-operated cut-off grinder with a cutting disc as the tool. The machine tool can be connected to at least two power supply devices in order to be supplied with electrical energy from the power supply devices. The power supply devices of the machine tool can, for example, deliver a voltage of more than 20 volts (V). A nominal voltage between 21 and 22 V is particularly preferred.The machine tool may also have three or more power supply devices. Those skilled in the art will appreciate that this voltage may vary depending on the charge level of the power supply devices.

[0025] The cutting disc is a disc-shaped tool of the power cutter that can be braked and brought to a standstill using the proposed braking method. The cutting disc can have a diameter that is, for example, greater than 230 millimeters (mm). For example, the cutting disc can have diameters of 300 mm, 250 mm, or 400 mm, but are not limited to these. The weight of the cutting disc can, for example, be in a range between 200 and 2,500 grams, i.e., between 0.2 and 2.5 kilograms (kg). For example, the weight of the cutting disc can assume values ​​of 210 grams, 530 grams, 550 grams, 930 grams, 1,270 grams, 1,280 grams, 1,720 grams, or 2,450 grams, but are not limited to these. For example, the cutting disc can be a diamond cutting disc or an abrasive cutting disc with bonded abrasive grains.A diamond cutting disc is preferably characterized by having a steel core with diamond segments. Of course, the invention is not limited to use in a cut-off machine; the proposed method can be used in many other machine tools or electrical devices used on a construction site.

[0026] Further advantages emerge from the following description of the figures. The figures, the description, and the claims contain numerous features in combination. Those skilled in the art will expediently consider the features individually and combine them into further meaningful combinations. In the figures, identical and similar components are numbered with the same reference numerals.

[0027] They show:

[0028] Fig. 1 Possible block diagram for calculating the recuperation limits in a series connection of several energy supply devices

[0029] Fig. 2 schematic representation of a machine tool with two energy supply devices

[0030] Implementation examples and figure descriptions:

[0031] Figure 1 shows a possible block diagram for calculating the recuperation limits in a series connection of several energy supply devices 14, 16 in a machine tool 10. The machine tool 10 is shown schematically in Figure 2. The block diagram shown in Figure 1 shows in particular the method steps S1: control of the recuperation or the braking process and S2: calculation of the unbalance factor k_Unbalance.

[0032] According to the block diagram shown in Figure 1, the voltages measured during recuperation for the individual energy supply devices 14, 16 in the machine tool 10 are used to calculate the factor k_Unbalance. Figure 1 shows, in particular, the voltages of the first energy supply device 14, the second energy supply device 16, and an nth energy supply device (without reference symbol), which are included in the calculation of the factor k_Unbalance. The factor k_Unbalance can then be multiplied by the limit value U_Akkupack, Limit of the energy supply devices 14, 16, and the number n of energy supply devices 14, 16, with the multiplication symbolized by the "x" in the block diagram. In this way, the limit value U_Zwischen kreis, Limit for the intermediate circuit voltage is obtained.This limit value U_Zwischenkreis, Limit for the intermediate circuit voltage is then used for process step S1: Control of recuperation or braking. The maximum permissible recuperation current l_Rekuperation, Limit can also be incorporated into the control of recuperation or braking. The maximum permissible recuperation current l_Rekuperation, Limit preferably represents the limit value for the recuperation current l_Rekuperation. The limit value l_Rekuperation, Limit for the recuperation current is preferably calculated from the minimum of the recuperation current limit values ​​of the individual energy supply devices 14, 16, which are connected in series in the proposed machine tool 10. The calculation from the minimum is expressed in the block diagram shown in Figure 1 by the designation "min".The recuperation current limit value of the first energy supply device 14 is preferably referred to in Figure 1 as l_Rekuperationlimit, Akku, 1, while the limit value for the recuperation current for the second energy supply device 16 is preferably referred to in Figure 1 as l_Rekuperationlimit, Akku, 2. The limit value for the recuperation current for the nth energy supply device is preferably referred to in Figure 1 as l_Rekuperationlimit, Akku, n.

[0033] Figure 2 shows a schematic representation of a machine tool 10 with two power supply devices 14, 16. The machine tool 10 can also have a motor 12, which is preferably designed as a brushless motor. Of course, the machine tool 10 can also have many other components, such as electronics, a tool 18, a tool holder, and / or holders for the power supply devices 14, 16, without being limited thereto. The tool 18 of the machine tool 10 can be surrounded by a blade guard (no reference numeral) to protect the user of the machine tool 10 from flying sparks or chips. Of course, the machine tool 10 can also have handles (no reference numeral) with which the user can transport the machine tool or guide it during work.

[0034] List of reference symbols

[0035] 10 Machine tool

[0036] 12 Motor 14 first power supply device

[0037] 16 second power supply device

[0038] 18 tools

[0039] 51 Control of recuperation or braking

[0040] 52 Calculating the imbalance factor

Claims

Patent claims 1 . Method for braking a machine tool (10), wherein the machine tool (10) is a battery-operated machine tool and is connectable to at least a first energy supply device (14) and a second energy supply device (16) in order to be supplied with electrical energy, wherein electrical energy released during braking of the machine tool (10) is fed back into the first energy supply device (14) and / or the second energy supply device (16) of the machine tool (10), wherein the energy supply devices (14, 16) are connected in series, characterized in that a limit value of the intermediate circuit voltage U_Intermediate circuit, Limit is smaller than a sum of the limit values ​​of the voltages U_Battery pack, Limit of the energy supply devices (14, 16).

2. Method according to claim 1, characterized in that the limit value of the intermediate circuit voltage U_Zwischenkreis,Limit is obtained by multiplying the limit value of the voltages U_Akkupack,Limit by a number n of the energy supply devices (14, 16) and a factor k_Unbalance.

3. Method according to claim 2, characterized in that the factor k_Unbalance lies between 0 and 1.

4. Method according to one of the preceding claims, characterized in that a limit value of a recuperation current l_Rekuperation, Limit is not exceeded.

5. Method according to claim 4, characterized in that the limit value of a recuperation current l_Rekuperation, Limit corresponds to a minimum of the Limit values ​​of the recuperation currents of the energy supply devices (14, 16).

6. Machine tool (10) for carrying out the method according to one of the preceding claims.

7. Machine tool (10) according to claim 6, characterized in that a motor (12) of the machine tool (10) is a brushless motor.

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