Method for braking a machine tool, 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 electrical energy that is generated when braking the machine tool is fed back into an energy supply device of the machine tool. The invention makes use of the basic concept that the braking power is reduced when the energy supply device has reached its limits for absorbing electrical energy. This reduction in braking power can be achieved by shortening a current space vector with the help of correction factors or by rotating it within a space vector representation. The invention also relates to a machine tool for carrying out the braking method.

Description

[0001] METHOD FOR BRAKING A MACHINE TOOL

[0002] AND MACHINE TOOL

[0003] The present invention relates to a method for braking a machine tool, wherein the machine tool is a battery-operated machine tool and electrical energy released during braking of the machine tool is fed back into a power supply device of the machine tool. The invention utilizes the basic idea that the braking power is reduced when the power supply device of the machine tool has reached its limits for absorbing electrical energy. This reduction in braking power can be achieved by shortening a current space vector using correction factors or by rotating it in a space vector representation. In a second aspect, the invention relates to a machine tool for carrying out the braking method.

[0004] Background of the invention:

[0005] In the field of machine tools, it is known to brake machine tools to complete a task or for safety reasons. The following braking methods are known in particular in the prior art: short-circuit braking, the use of a brake chopper as a braking resistor, and recuperation.

[0006] During short-circuit braking, the machine tool motor is short-circuited. This can be achieved, for example, by switching on all of the low-side semiconductors of the motor inverter at the same time. An initially high short-circuit current can develop, which then changes into a continuous short-circuit current. The short-circuit current generates a braking torque in the machine tool motor with which the machine tool or its tool can be braked. The disadvantage of short-circuit braking is that the user has little influence on the braking torque or the braking time. The level of the short-circuit current is determined solely by the motor parameters. In addition, the machine tool electronics must be able to carry the comparatively high initial short-circuit current at the start of short-circuit braking. If the machine tool is not designed to withstand such short-circuit currents, this can lead to damage to the machine tool or its tool.their electronics. When using a brake chopper as a braking resistor, the machine tool motor can be braked in a controlled manner, so that it acts as a generator. The energy output can be fed back into an intermediate circuit of the machine tool’s electronics. The machine tool can have a brake chopper as a braking resistor, whereby the brake chopper is designed to connect a resistor to the intermediate circuit in order to convert the energy in the braking resistor into heat. Although the use of a brake chopper allows more freedom in achieving certain desired braking torques or braking times, one disadvantage of using a brake chopper is that at least one additional hardware component has to be installed in the machine tool. This increases the weight of the machine tool and its volume. A larger volume can, for example, have a negative impact on ergonomics orThe handling of the machine tool suffers. The installation of a brake chopper often also requires additional electronic components, such as MOSFETs, gate drivers, or connecting wires, which can complicate the manufacture and assembly of the machine tool. Especially if the brake chopper is designed for high pulse power, the costs for the machine tool and the space required inside the machine tool can increase significantly.

[0007] Regeneration is only possible if regenerative energy supply devices are used in the machine tool. The machine tool motor can be braked in a controlled manner during recuperation, thus acting as a generator. The energy output can be fed back into the intermediate circuit and from there transferred to the energy supply devices. The quality and recuperation capacity of the machine tool depend largely on the energy supply device installed in the machine tool. During braking processes where, for example, the braking current must be constant or a braking ramp is specified, operating conditions can arise that place such a load on the energy supply device that limit values ​​relating to, for example, the electrical properties of the energy supply device, such as voltage or current carrying capacity, can be exceeded. This can cause damage to the energy supply device.To avoid exceeding these limits, the current state of the art is to perform the braking process as slowly as possible. However, this is not a good idea, especially if rapid deceleration of the machine tool is desired, for example, to quickly and safely protect the machine tool user from injury.

[0008] 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 braking a machine tool, as well as a machine tool, so that, on the one hand, the most effective protection for a user of the machine tool can be enabled, and, on the other hand, a compact, handy machine tool can be provided. Furthermore, the released energy should be fed back into the power supply device as effectively as possible in order to provide a machine tool that is as resource-efficient as possible and has a good battery range.

[0009] 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.

[0010] Description of the invention:

[0011] According to the invention, a method for braking a machine tool is provided, wherein the machine tool is a battery-operated machine tool and electrical energy released during braking of the machine tool is fed back into a power supply device of the machine tool. The braking method is characterized by the following method steps: a) operating the machine tool under specification of a first current value, b) feeding the electrical energy released during braking of the machine tool back into the power supply device of the machine tool, c) reducing a braking power of the machine tool if at least one limit value of the power supply device is exceeded, d) continuing to operate the machine tool with target current values, wherein the target current values ​​are determined based on the reduction in the braking power of the machine tool and the first current value.

[0012] The method can, on the one hand, enable the shortest possible braking time, and on the other hand, provide a compact, handy machine tool. The particularly short braking time allows the user of the machine tool to be particularly effectively protected from injury. The proposed method advantageously enables recuperation, i.e. feeding electrical energy back into a power supply device in a machine tool, with particularly high efficiency. The proposed method can be described as efficient generator braking operation without a brake chopper. The method advantageously makes it possible to feed the released braking energy back into the power supply device particularly efficiently. According to the invention, it is preferred that the machine tool be connectable to at least one power supply device for supplying it with electrical energy.For example, the machine tool can have receiving areas or options for coupling one, two or more energy supply devices, such as batteries or accumulators ("accumulators"). For the purposes of the invention, it is preferred that the terms accumulator ("accumulator"), battery and energy supply device are used synonymously. The electronics of the machine tool and its motor are preferably operated at an optimal operating point with particularly low power loss. To achieve this, the machine tool can, for example, be operated along a power loss-optimized characteristic curve. The formulation that the machine tool is operated along a power loss-optimized characteristic curve preferably means, for the purposes of the invention, that the losses when operating the machine tool can be minimized with the invention. These can be, for example, iron and / or copper losses.The formulation that the operation of the machine tool takes place along a power loss-optimized characteristic curve can, in the sense of the invention, also mean that the machine tool is operated in an optimized manner with regard to the current yield and / or the efficiency.

[0013] According to the invention, it is preferred that the machine tool is operated along an MTPA characteristic curve in a space vector representation, where the abbreviation MTPA stands for “maximum torque per ampere,” i.e., maximum torque per ampere. This advantageously allows the machine tool to be operated with optimal current efficiency. It has been shown that the machine tool can be operated with particularly low losses or power losses in this way. Preferably, in the context of the invention, a maximum motor stator target current l_S, max is specified, which, according to the invention, is preferably also referred to as maximum motor current l_S, max. This maximum motor current l_S, max can thus represent a first current value according to the invention. However, if the feedback or feedback power is too high, limit values ​​intended to ensure safe operation of the energy supply device may be exceeded.These limit values ​​can relate to the voltage and / or the current of the energy supply device. In the sense of the invention, they are referred to as limit values ​​of the energy supply device or as "battery limit values". In the sense of the invention, it is preferred that the battery limit value for the voltage is referred to as U_Akku, max and the battery limit value for the current is referred to as l_Akku, max. Alternatively or additionally, the first current value can be the motor target current l_S, soll. In the sense of the invention, it is preferred that the exceeding of the battery limit values ​​is prevented by actively controlling the battery voltage and / or the battery current. For this purpose, a reduction in the braking power of the machine tool is initiated, preferably after an exceedance of at least one of the battery limit values ​​has been detected.According to the invention, target current values ​​are calculated and output, with the determination of the target current values ​​being based on the reduction in the braking power of the machine tool and the first current value. It is preferred within the meaning of the invention that the target current values ​​from method step d) of the proposed method are target current values ​​for the d and q axes of the space vector representation. The target current values ​​for the d and q axes can thus represent modified or second current values ​​with which the operation of the machine tool can be continued.By continuing to operate the machine tool with the modified target current values, preferably for the d and q axes of the space vector representation, a reduction in the braking power of the machine tool can be ensured so that the limit values ​​of the energy supply device are not exceeded, but a safe and fast braking of the machine tool is still possible.

[0014] In a particularly preferred embodiment of the invention, the machine tool can, for example, be operated with a target motor current l_S, soll. Furthermore, a maximum motor current l_S, max can be specified, wherein the braking power of the machine tool is reduced if at least one limit value of the energy supply device is exceeded. The braking power of the machine tool can be reduced in particular by rotating a current space vector l_S, max in the space vector representation by applying a changed braking angle ß_brems such that a length of the current space vector l_S, max remains essentially unchanged. By rotating the current space vector l_S, max, the changed target current values, preferably for the d and q axes of the space vector representation, can be determined and the braking power of the machine tool can be reduced in this way.In this embodiment of the invention, it is preferred that the target current values, preferably for the d and q axes of the space vector representation, are determined with the aid of the maximum stator current l_S, max and the braking angle ß_brems, wherein the target current values, preferably for the d and q axes, are to be used as the output or manipulated variable for the further braking process.

[0015] In one embodiment, the invention relates to a method for braking a machine tool, wherein the machine tool is a battery-operated machine tool and electrical energy released when the machine tool is braked is fed back into a power supply device of the machine tool.The method is characterized by the following method steps: a) operation of the machine tool along an MTPA characteristic curve in a space vector representation under specification of a first current value, b) feedback of the electrical energy released when braking the machine tool into the energy supply device of the machine tool, c) reduction of a braking power of the machine tool if at least one limit value of the energy supply device is exceeded, d) continued operation of the machine tool with target current values ​​for the d and q axes of the space vector representation, wherein the target current values ​​for the d and q axes are calculated based on the reduction in the braking power of the machine tool and the first current value.

[0016] According to the invention, it is preferred that a correction factor k_Dreh can also be determined in the case of a rotation of the current space vector l_S,max. Preferably, the correction factor k_Dreh can be applied to an angular position of the current space vector l_S,max, so that a rotation of the current space vector l_S,max with a modified braking angle ß_brems is obtained.

[0017] In a further particularly preferred embodiment of the invention, the braking power of the machine tool can be reduced by determining at least one correction factor k and applying it to the maximum motor current l_S, max. This makes it possible to obtain a reduced setpoint value l_S, red for the motor current, based on which the changed setpoint current values, preferably for the d and q axes of the space vector representation, are then determined and the braking power of the machine tool is reduced in this way. The reduced setpoint value l_S, red for the motor current can be passed on to a motor current controller so that the motor current can be regulated or adjusted based on the reduced setpoint value l_S, red. In the sense of the invention, it is preferred that in this embodiment the braking power of the machine tool is reduced by shortening the current space vector.In other words, the application of the correction factor k to the maximum motor current l_S, max leads to a shortening of the current space vector, whereby the braking power of the machine tool can advantageously be reduced. In a further particularly preferred embodiment of the invention, the machine tool can be operated subject to the specification of the maximum motor current l_S, max. The braking power of the machine tool can be reduced either by determining at least one correction factor k and applying it to the maximum motor current l_S, max, so that a reduced setpoint l_S, red is obtained for the motor current, or by rotating the current space vector l_S, max in the space vector representation, so that a length of the current space vector l_S, max remains essentially unchanged.The rotation of the current space vector l_S, max can preferably be carried out by applying a changed braking angle ß_brems to the current space vector l_S, max.

[0018] By rotating the current space vector l_S,max, the operating point of the machine tool motor can be set to a lower torque and thus also a lower braking power without reducing the stator current amplitude. This high stator current can then cause further high losses within an inverter, the electronics, and / or the motor, so that the braking energy can be absorbed and converted into heat. Preferably, even with limited power consumption, a surprisingly large power loss can be dissipated in the electronics, the inverter, and / or the motor of the machine tool when feeding electrical energy back into the power supply device. This can advantageously create an additional power sink and make the braking process even faster.In particular, by applying the modified braking angle ß_brems and the resulting rotation of the current space vector l_S,max in the space vector representation, a regenerative braking operation, which is subject to high losses, can be provided for a machine tool to decelerate its tool. The proposed method initially does not require a braking chopper. Preferably, the braking angle ß_brems can also be referred to as the "stator current space vector angle ß_brems" within the meaning of the invention.

[0019] According to the invention, it is preferred that, when the current space vector l_S, max is rotated to reduce the braking power, the battery voltage regulator and the battery current regulator are used to determine and output correction factors as a manipulated variable. Such a reduction in braking power is particularly preferred when the energy supply device and an optional braking resistor, such as a braking chopper, have reached their maximum power consumption. This advantageously ensures that battery limit values ​​are adhered to and that the energy supply device is not damaged. In particular, by rotating the current space vector, an operating point in the space vector representation with a reduced braking torque can be obtained. The reduced braking torque can be obtained in particular by a shortened current space vector and / or by a rotated current space vector.

[0020] The correction factor k can comprise various components or be formed from different individual correction factors. For example, a correction factor k_U,red can be provided for the battery voltage and / or a correction factor k_l,red for the battery current regulator. In addition to the correction factors k_U,red and k_l,red, the duty cycle of an optional brake chopper can also be taken into account when calculating the braking angle. In other words, it can be preferred within the meaning of the invention that the combined correction factor k_red also comprises a component that is related to the duty cycle of the brake chopper. This is particularly the case if the machine tool has a brake chopper. These correction factors can be summarized under the designation correction factor k, whereby the generic term for the correction factors is referred to as “k_red” in the block diagrams.Within the meaning of the invention, it is preferred that the combined correction factor k_red also includes a component related to the duty cycle of the brake chopper. This is particularly true if the machine tool has a brake chopper. The correction factor k can thus represent the battery voltage correction factor k_U,red or the battery current correction factor kJ,red or a correction factor that reflects the duty cycle of the brake chopper. Furthermore, the correction factor k can be a mixed correction factor that includes components of these aforementioned correction factors or subsets of these correction factors.

[0021] The ability of a brake chopper to absorb electrical energy may be limited if a duty cycle of 100% or substantially 100% is reached. To circumvent such a limitation due to the duty cycle, it may be preferable within the meaning of the invention to use a comparatively low-resistance brake chopper. The brake chopper may preferably have an electrical resistance in a range of 0.1 to 2 ohms. Such brake choppers or braking resistors are preferably referred to as "low-resistance brake choppers" within the meaning of the invention.

[0022] If the machine tool includes a brake chopper, the energy distribution in the proposed braking method can be described as follows: First, the released braking energy is fed back into the energy supply device. If the energy supply device can no longer absorb the braking energy or braking power, the remaining excess energy can be fed into the brake chopper. If the brake chopper can no longer absorb the braking energy or braking power, the motor's braking power can be reduced by using a smaller braking torque.

[0023] Preferably, the braking angle ß_brems can also be referred to as the "stator current space vector angle ß_brems" within the meaning of the invention. This braking angle ß_brems can be calculated in the context of the present invention as follows: ßbrems = kred ' ( ßBrake, MTPA ~ ßBrake, 0 Nm ) + ßBrake, 0 Nm-

[0024] The parameter ßbrems, MTPA preferably corresponds to the angle on the MTPA characteristic curve, while the parameter ßbrems, o Nm corresponds to the current space vector angle with which an operating point with a torque generation of 0 Nm or essentially 0 Nm is reached. This operating point can, for example, lie in the third quadrant or the fourth quadrant of the space vector representation. The third quadrant should explicitly include the boundary to the second quadrant (upper limit of the third quadrant), and the fourth quadrant should explicitly include the boundary to the first quadrant (upper limit of the fourth quadrant). As can be seen in Figure 2a, the intersection point of the current limit circle K with the 0 Nm characteristic curve of the space vector representation lies at the boundary between the third and second quadrant, and preferably no torque is generated. As can be seen in Figure 2b, the intersection point of the current limit circle K with the 0 Nm characteristic curve can also lie in the fourth quadrant.From the maximum stator current l_S, max and the current space vector angle ßbrems, the target current values, preferably for the d-axis and the q-axis of the space vector representation, can advantageously be calculated.

[0025] It is preferred in the sense of the invention that the braking torque is reduced by the rotated braking angle or stator current space vector angle ß_brems, while the losses in the inverter and / or in the motor of the machine tool continue to absorb the maximum braking power due to the essentially constant motor current amplitude, so that in summary, a particularly rapid braking of the tool of the machine tool can be achieved with the invention.

[0026] According to the invention, it is preferred that an operating range of a current space vector l_S is limited by a correction factor k in its length and / or in its current vector angle, so that a first limit value U_Akku, max and / or a second limit value l_Akku, max of the energy supply device is / are not exceeded. Preferably, an operating range of a current space vector l_S can be limited by a current limit of an inverter of the machine tool, wherein in particular the provision of a correction factor K, which can be applied to a length and / or an angle of the current space vector l_S, advantageously results in the limit values ​​for voltage and / or current of the energy supply device not being exceeded.According to the invention, it is preferred that the longest current space vector l_S lies on the MTPA characteristic curve, which is preferably limited by the current limit of the machine tool inverter when unlimited recuperation of electrical energy into the power supply device of the machine tool occurs. Limiting the operating range of the current space vector l_S by the current limit of the machine tool inverter can be achieved, in particular, by limiting the current space vector l_S to the limit values ​​U_Akku, max and / or limit l_Akku, max when they are reached, so that the limit values ​​of the power supply device are not exceeded.

[0027] According to one embodiment of the present invention, exceeding these limit values ​​of the energy supply device can be prevented by determining at least one correction factor k and applying it to the maximum motor current l_S, max , such that a reduced setpoint l_S, red is obtained for the motor current. Advantageously, this makes it possible to actively regulate the battery voltage and / or the battery current and to provide a balanced compromise between maximum feedback efficiency and battery protection. The at least one correction factor k is preferably determined in a controller provided for this purpose, wherein a voltage correction factor k_U, red can be provided by a voltage regulator and a current correction factor kJ, red can be provided by a current regulator within the electronics of the machine tool.The voltage and current regulators are preferably voltage and current regulators of the energy supply device. Preferably, the battery voltage regulator is thus set up to determine a battery voltage correction factor k_U, red, while the battery current regulator is set up to determine a battery current correction factor kJ, red. The corresponding correction factors k_U, red and kJ, red can preferably assume values ​​in a range between 0 and 1. A reduced motor stator target current l_S, red is preferably output as an output variable for this control or correction process. According to the invention, this reduced motor stator target current l_S, red is also referred to as reduced motor current l_S, red. The fixed, predetermined maximum motor current l_S, max can thus be adjusted using the correction orReduction factors k_U, red and kJ, red are multiplied so that a reduced target current value l_S, red can be passed on to the motor current controller. Preferably, a first current value, for example the maximum motor current l_S, max, can be multiplied by the battery voltage correction factor k_U, red and / or the battery current correction factor kJ, red in order to obtain target current values, preferably for the d- and q-axes, as second current values ​​within the meaning of the invention, with which the machine tool can continue to be operated.

[0028] The corresponding space vector representation (see Figure 1) shows the operating range AB of the so-called current space vector l_S. Without limiting energy recovery, i.e., "battery recuperation," the longest current space vector l_S results on the MTPA characteristic curve.

[0029] The current space vector l_S represents in particular a stator current space vector, i.e. in particular the space vector for the stator current of the electric motor of the machine tool is represented. According to the invention, it is preferred that the current space vector l_S is limited by a current limit of the inverter of the electronics of the machine tool. This current limit of the inverter is also shown in the space vector representation shown in Figure 1, specifically as a circle K. Preferably, the current space vector l_S can be shortened when the battery limit value for the voltage (U_Akku, max) is reached and / or when the battery limit value for the current (l_Akku, max) is reached, such that the battery limit values ​​are not exceeded. The shortening of the current space vector l_S is preferably carried out by applying the at least one correction factor k.

[0030] The term “correction factor k” is a generic term for various correction factors. These can be, for example, the correction factors k_U, red and kJ, red for limiting the maximum motor current l_S, max to a reduced motor current l_S, red, wherein in the context of the invention at least one correction factor k is applied to the setpoint for the maximum motor current. A further correction factor k_red can, for example, ensure a limitation of the duty cycle when a brake chopper is used, i.e. when electrical energy is not only fed back into the energy supply device, but also into a brake resistor, which in the sense of the invention is preferably referred to as a “brake chopper”. In the sense of the invention it is preferred that the at least one correction factor k lies in a value range between 0 and 1.

[0031] It is preferred within the meaning of the invention that the at least one correction factor k is composed of a first correction factor k_U, red, a second correction factor k_l, red and / or a third correction factor k_red, wherein the first correction factor k_U, red is determined by a voltage regulator of the energy supply device and the second correction factor k_j, red is determined by a current regulator of the energy supply device and the third correction factor k_red is used to limit a duty cycle. It is preferred within the meaning of the invention that the at least one correction factor k corresponds to a first correction factor k_U, red, which is determined by a voltage regulator of the energy supply device, or corresponds to a second correction factor k_l, red, determined by a current regulator of the energy supply device or corresponds to a third correction factor k_red for limiting a duty cycle.

[0032] The voltage regulator and the current regulator of the energy supply device are provided, in particular, for determining the corresponding correction factors k_U, red and kJ, red when no brake chopper is used. The machine tool or its electronics can furthermore or additionally comprise further regulators. In particular, when a brake chopper is used in the context of the invention, the machine tool or its electronics can comprise three regulators. For example, a first regulator can be provided, which is preferably designed as a two-point regulator with hysteresis and is configured to control the brake chopper. It is preferred within the meaning of the invention that this first regulator is designed as a comparator with switching hysteresis, wherein the first regulator preferably comprises an upper switch-on threshold and a lower switch-off threshold or is characterized by such thresholds.The first controller is designed in particular to compare an intermediate circuit voltage or a voltage U_Akku of the energy supply device with a reference voltage U_Chopper of the brake chopper. The output signal of the first controller can preferably represent or form a signal for pulse width modulation (PWM), wherein the first controller outputs a high-level signal in particular when the voltage U_Akku of the energy supply device is greater than the reference voltage U_Chopper of the brake chopper. In other words, the first controller is designed to output a PWM signal which is a high level in particular when U_Akku > U_Chopper. The PWM signal can have a duty cycle, wherein the duty cycle can be formed, for example, by a low-pass filter.

[0033] In an alternative embodiment of the invention, the first controller can also be designed as a PI controller. It is preferred within the meaning of the invention that the output variable of the first controller, which is preferably designed as a PI controller, is a duty cycle for the brake chopper. Control pulses for the brake chopper can preferably be generated from this duty cycle. A PWM module, for example, can be used for this purpose. In other words, the PWM module can be designed to generate control pulses for a brake chopper from a duty cycle output by a PI controller. The machine tool or its electronics can have a second controller designed to monitor the limit values ​​of the energy supply device. The limit values ​​of the energy supply device can, for example, relate to the voltage and / or the current; they are accordingly preferably referred to as U_Akku, max or l_Akku, max.It is particularly preferred within the meaning of the invention that the second controller is configured to regulate the current of the power supply device, i.e., the "battery current," to the limit value l_Akku, max. Preferably, the second controller outputs the reference voltage U_Chopper for the brake chopper as a manipulated variable, wherein this output voltage U_Chopper can in turn be regulated to the maximum value or the limit value U_Akku, max to ensure that the maximum permissible "battery voltage," i.e., the voltage of the power supply device, is not exceeded.

[0034] The machine tool or its electronics can have a third controller that is used to limit duty cycles. The third controller can be designed in particular to regulate the duty cycle to a target value D_Soll of a maximum of approximately 95% of the switch-on duty cycle of the brake chopper. The third controller can output a correction or reduction factor k_red as an output variable, which, like the two other correction factors k_U, red and kJ, red, lies in a value range between 0 and 1. Preferably, the correction factor k_red is referred to as the “third correction factor” within the meaning of the invention. It is preferred within the meaning of the invention that the third correction factor k_red is multiplied by the maximum motor stator target current l_S, max. In this way, the reduced motor stator target current l_S, red can advantageously be obtained or determined.

[0035] The machine tool or its electronics can have a limiting device for a rate of change of the motor current. The limiting device is preferably designed to provide a smooth transition from driving to braking of the machine tool or its tool. The limiting device can preferably also be referred to as a "rate of change limiter of the motor current" within the meaning of the invention. It is preferred within the meaning of the invention that the limiting device avoids a jump in the motor stator target current to the maximum motor stator current l_S,max by only permitting a maximum rate of change of the motor stator target current. The rate of change is preferably specified in the physical unit "amperes per second", i.e., amperes / second or A / s. A limiting device can be provided as an optional component on the machine tool.The limiting device can then be represented as an additional block in the block diagrams of Figures 3-6, which enables a particularly smooth transition from driving to braking. The proposed braking method is described using field-oriented control (FOC). However, within the meaning of the invention, it is also preferable to implement the method with block commutation. In the language of space vector representation, the operating range of the current or stator current space vector is shown in Figures 2a and 2b.

[0036] The machine tool can comprise a brake chopper, wherein electrical energy released when the tool of the machine tool is braked is absorbed by the brake chopper. The braking method that makes use of the brake chopper represents a recuperation method with efficient generator-type braking operation with a brake chopper. It is preferred within the meaning of the invention that the stator current l_S is only reduced when at least one of the limit values ​​of the energy supply device, for example U_Akku, max and / or l_Akku, max, has reached the corresponding limits. It can also be preferred within the meaning of the invention that the stator current l_S is reduced when the switch-on duty cycle of the brake chopper has reached its limit.

[0037] The use of a brake chopper is particularly advantageous when the power consumption is limited by the energy supply device, for example because critical limits of the energy supply device are exceeded. According to the invention, it is preferred that the brake chopper, in addition to the energy supply device, can absorb electrical energy that is released when the machine tool is decelerated. Preferably, the energy supply device can absorb a basic amount of electrical energy, and the brake chopper can be provided as an optional component on the machine tool in order to absorb additional electrical energy that the energy supply device can no longer absorb due to possible technical limitations. This advantageously makes it possible to provide higher braking power.It has been shown that when a brake chopper is provided, the influence of the energy supply device on the braking torque and the braking time is less than in braking methods that do not require a brake chopper. According to the invention, it is preferred that the maximum power loss within the brake chopper is limited depending on the design. The limitation is achieved in particular when a duty cycle, in particular a switch-on duty cycle, of the brake chopper is 100% or essentially 100%. The duty cycle or switch-on duty cycle can preferably also be referred to as duty cycle D according to the invention. If such a duty cycle or switch-on duty cycle of 100% or essentially 100% is achieved, it is preferred according to the invention that the braking power is reduced by a reduced motor current, in particular a reduced motor stator target current l_S, red.This is especially true because in this case the power supply device and the brake chopper have reached their maximum power consumption.

[0038] In one embodiment of the invention, the machine tool can be operated subject to a specification of a maximum motor current l_S, max, in particular a maximum motor stator target current l_S, max. A first correction factor k_U, red can be determined by a voltage regulator of the energy supply device and / or a second correction factor k_J, red can be determined by a current regulator of the energy supply device, wherein the correction factors can be applied to the maximum motor current l_S, max. In this way, a reduced target value l_S, red for the motor current can be obtained, which can be further converted into the second current values ​​for the continued operation of the machine tool, in particular the target current values ​​for the d and q axes in the space vector representation.According to the invention, it is preferred that the reduced setpoint l_S, red for the motor current be passed on to a motor current controller, so that the motor current can be regulated or adjusted based on the reduced setpoint l_S, red. This method results in a reduction in braking power by shortening the stator current space vector on the MTPA characteristic curve in the space vector representation. In particular, correction factors can be applied to reduce the value of a maximum motor current l_S, max to a reduced setpoint l_S, red for the motor current.

[0039] In a further embodiment of the invention, the machine tool can determine at least one correction factor k, which is applied to the maximum motor current l_S, max in order to obtain the reduced setpoint l_S, red for the motor current. The reduced setpoint l_S, red for the motor current can be passed on to a motor current controller so that the motor current can be regulated or adjusted based on the reduced setpoint l_S, red. This method also results in a reduction in braking power by shortening the stator current space vector on the MTPA characteristic curve in the space vector representation. In particular, the at least one correction factor can be applied to reduce the value of a maximum motor current l_S, max to a reduced setpoint l_S, red for the motor current.

[0040] According to the invention, it is preferred that the tool of the machine tool is stopped with a braking time in the range of 2 to 4 seconds. Braking the tool of the machine tool with a braking time between 2 and 4 seconds (s) can, in particular, protect the parts and components in the drive train of the machine tool. According to the invention, it is preferred that the braking torque of the machine tool can be adjusted so that braking times between 2 and 4 seconds can be achieved.

[0041] If a kickback event is detected by the machine tool, it may be preferable within the meaning of the invention for the tool of the machine tool to be stopped with a braking time of less than 1.5 seconds, preferably less than 1 second, most preferably less than 0.5 seconds. In this way, the tool of the machine tool can be braked as quickly as possible in order to optimally protect the user of the machine tool from injury. The wording that the machine tool or its tool is stopped means, within the meaning of the invention, that the tool of the machine tool is brought to a standstill. However, the wording that the machine tool or its tool is stopped can just as well mean, within the meaning of the invention, that the tool is deprived of a large part of its rotational energy and that the tool of the machine tool only continues to rotate in a speed range that is less dangerous for the user.The phrase “majority of its rotational energy” can, within the meaning of the invention, preferably mean that more than 50% of the rotational energy of the tool is converted into another form of energy and / or fed back into the energy supply device. Within the meaning of the invention, it is very particularly preferred that, in the context of the proposed braking method, more than 60%, 70%, 80%, 90%, or 95% of the rotational energy of the tool is converted into another form of energy and / or fed back into the energy supply device. Preferably, the tool of the machine tool can be braked with a braking time of less than 1.5 seconds, preferably less than 1 second, most preferably less than 0.5 seconds, such that the tool of the machine tool loses a large part of its rotational energy.In the context of the invention, this preferably means that more than 50%, preferably more than 60%, 70%, 80%, 90%, or 95% of the rotational energy is extracted from the tool of the machine tool, and that more than 50%, preferably more than 60%, 70%, 80%, 90%, or 95% of the rotational energy is converted into another form of energy and / or fed back into the energy supply device. Of course, all intermediate values ​​between 50 and 100%, which are intended to be understood by the phrase "majority of the rotational energy," are also possible, for example, more than 53%, more than 66.66%, more than 75%, more than 87.5%, or more than 93.76%.

[0042] The braking of the machine tool or its tool is achieved by the proposed braking method, in which the braking power of the machine tool is reduced when at least one limit value of the energy supply device is exceeded and the machine tool continues to operate with target current values, in particular for the d and q axes of the space vector representation. The target current values, in particular for the d and q axes, are calculated based on the reduction in the braking power of the machine tool and the first current value. The loss of rotational energy suffered by the tool of the machine tool due to braking can advantageously be fed back into the energy supply device of the machine tool, so that this energy is later available again for the further energy supply of the machine tool.In other words, the energy supply device of the machine tool can be at least partially recharged by the proposed braking method in which rotational energy released when the machine tool or its tool is braked is fed back into the energy supply device of the machine tool, i.e. is recuperated. In this case, it is particularly preferred within the meaning of the invention that the tool or the machine tool does not have to be completely stopped, i.e. brought to a standstill, but that only a large part of the rotational energy is withdrawn or removed from the tool of the machine tool. The braking time t_down then preferably does not end when the tool comes to a standstill, but rather when the rotational speed n of the tool has reached a value of, for example, less than 70%, preferably less than 63%, 55%, 45%, 32%, 22% or an even lower proportion of the original rotational speed n_max.The time until the machine tool's tool actually comes to a standstill is then advantageously no longer important.

[0043] The braking time t_down, i.e. the time required for the machine tool to be stopped or brought to a standstill, is limited by the time values ​​t2 and t3. Braking of the machine tool or its tool preferably begins at time t2, while the machine tool's tool comes to a standstill at time t3. The standstill of the tool is equivalent to the tool rotating at 0% of the tool's original speed n_max. However, if only a large part of the tool's rotational energy is withdrawn or removed, the tool's speed is preferably reduced to less than 70%, more preferably less than 63%, 55%, 45%, 32%, 22% of the tool's original speed n_max, or to an even lower proportion or value. The corresponding end times of the braking time t_down are then preferably referred to in the sense of the invention as t3_70%, t3_63%, t3_55%, t3_45%, t3_32%, or t3_22%.For example, the braking time t_down can end at a time value t3_22%, where the time value t3_22% corresponds to a speed of 22% of the original speed n_max of the machine tool. Thus, the time value t3_22%, together with a speed value of 22% of the original speed n_max of the tool, forms a pair of values ​​that can be represented in a plot of speed n versus time t and, together with other pairs of values, forms the graph n(t). Such plots are shown in Figures 7 and 8. According to the invention, the following relationship exists between the rotational energy E and the speed n of the tool:

[0044] E = 1 / 2 * J * (2 * TT * n / 60) 2, where the letter J stands for the moment of inertia of the machine tool. This means that if the tool's speed n is reduced by 50%, only 25% of the original rotational energy E remains. Thus, in this example, the rotational energy E has been reduced by 75% if the tool's speed n is reduced to half its original value.

[0045] If a kickback event is detected by the machine tool, it may be preferred within the meaning of the invention that the tool of the machine tool is stopped with a braking time of less than 1.5 seconds, preferably less than 1 second, most preferably less than 0.5 seconds, wherein the braking time t_down can preferably not only be characterized by the standstill of the tool of the machine tool. Rather, the braking time can also end when the tool of the machine tool rotates at a speed of less than 70%, preferably less than 63%, 55%, 45%, 32%, 22% of the original speed n_max of the tool. Preferably, with this selection of the end point t3_x% of the braking time t_down, the time period until the tool of the machine tool actually comes to a standstill is no longer important. The letter x in the expression “t3_x%” preferably stands for any desired percentage value between 0 and 70% of the original speed n_max of the tool.

[0046] The term "kickback event" describes the sudden and unexpected occurrence of a force between a machine tool and the substrate being machined. For example, while the machine tool is machining a substrate, an unexpected movement of the machine tool or the machine tool itself can occur, which could endanger the user of the machine tool. Such a kickback event can occur, for example, if the machine tool tool becomes caught or jammed in the substrate, for example in a cutting gap. In addition, a kickback can occur if the substrate being machined has inhomogeneous material properties, such as steel reinforcement bars in concrete, or if a blunt tool is used. In all of these cases, it is desirable for the machine tool tool to be stopped as quickly as possible, i.e.to a standstill. This rapid braking is made possible by the invention because the braking time after detecting a kickback event is less than 1.5 seconds.

[0047] The rapid braking of the tool of the machine tool is preferably also expressed by the particularly low ratio of braking time to acceleration time of less than 1. This is because, within the meaning of the invention, it is particularly preferred that the ratio of braking time t_down to acceleration time t_up is less than 1. Within the meaning of the invention, this preferably means that the braking time t_down is less than the acceleration time t_up. In the case of a kickback, the ratio of braking time t_down to acceleration time t_up can even be less than 0.7, particularly preferably less than 0.5. Within the meaning of the invention, such a ratio of less than 0.5 preferably means that the braking time t_down is less than half the acceleration time t_up. Within the meaning of the invention, the term “acceleration time t_up” preferably stands for the period of time that the machine tool requires to reach a maximum speed n_max from a standstill.If the standstill of the machine tool is assigned time t0 and the first reaching of the maximum speed is assigned time t1, the time span of the “acceleration time t_up” extends between times t0 and t1. The term “braking time t_down” in the sense of the invention preferably stands for the time span that the machine tool requires to come from this maximum speed n_max to the standstill in which the tool of the machine tool no longer rotates, i.e. the speed n assumes the value “0”, n = 0 revolutions per minute (rpm). If the standstill of the machine tool is assigned time t3 and the start of the braking process is assigned time t2, the time span “braking time t_down” extends between times t2 and t3. In the time span between t1 and t2, the machine tool can be worked on, for example by operating it at different speeds.According to the invention, it is preferred that the machine tool comprises a speed controller for adjusting a speed. Preferably, the short braking times in "normal" braking situations and upon detection of a kickback event can be achieved by the proposed braking method, i.e., by feeding the rotational energy stored in the machine tool back into a power supply device of the machine tool, for example, and by reducing the braking power of the machine tool when the power supply device of the machine tool has reached its limits for absorbing electrical energy.

[0048] It is preferred within the meaning of the invention that the kickback event is detected with the aid of a sensor device. In other words, the machine tool can comprise a sensor device that is configured to detect kickback events or other emergencies reliably, quickly, and accurately. It can also be preferred within the meaning of the invention that the existing electronics or electronics present in the machine tool are used to detect kickback events. For this purpose, for example, operating parameters of the machine tool, such as current, the speeds of the motor and / or spindle, accelerations, or electrical energy, about which information is already available or known in the machine tool, can be evaluated in order to detect the onset of a kickback event.In the sense of the invention, it may also be preferable to provide detection devices, such as sensors, on the machine tool in order to determine and evaluate the said operating parameters in order to reliably and quickly detect kickback events or other emergencies.

[0049] 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 motor of the machine tool is 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. It is particularly preferred within the meaning of the invention for the machine tool to be a battery-operated cut-off grinder with a cutting disc as the tool. The machine tool can be connected to at least one energy supply device in order to be supplied with electrical energy from the energy supply device.The at least one power supply device of the machine tool can, for example, deliver a voltage of more than 20 volts (V). A voltage between 21 and 22 V is particularly preferred. The machine tool can also have two or more power supply devices. If the machine tool has more than one power supply device, the electrical energy released when the machine tool decelerates can be fed back into the first and / or second power supply device. This recuperation can occur substantially simultaneously, sequentially, or according to a specially designed algorithm.

[0050] 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 in that it has a steel core with diamond segments.

[0051] It is preferred within the meaning of the invention that the motor of the machine tool is controllable using field-oriented control or block commutation. In a preferred embodiment of the invention, it is preferred that the braking angle ß_brems can be changed in order to reduce the braking power of the machine tool and to rotate the current space vector l_S, max in the space vector representation. If the motor of the machine tool is controlled using block commutation, it can also be preferred within the meaning of the invention that the commutation angles are changed in order to reduce the braking power of the machine tool. In a preferred embodiment, the commutation angles are changed such that the resulting commutation blocks are lagging. The machine tool can comprise a braking chopper, wherein the braking chopper is configured to absorb electrical energy released when the tool of the machine tool is braking.The brake chopper is particularly designed to absorb additional electrical energy in addition to the energy supply device, which the energy supply device can no longer absorb due to a limited power consumption.

[0052] The following describes an exemplary embodiment of the invention, namely a braking method with recuperation and efficient regenerative braking operation with a brake chopper, as shown by way of example in Figure 4. In this embodiment of the invention, the PWM signal of the brake chopper can be generated as follows, with the PWM signal being generated in particular by the first controller, for example, a two-point controller. The first controller can comprise a comparator or be formed by a comparator. The comparator is configured to compare the battery voltage u_Akku with the output control variable of the battery current controller U_Chopper.

[0053] If the battery voltage u_Akku—possibly plus a hysteresis contribution—is greater than the reference voltage U_Chopper, a high level can be output at the PWM signal U_GatedriverinputPWM. Otherwise, a low level is output. According to the invention, it is preferred that the battery current ripple, the battery voltage ripple, and / or the resulting switching frequency be adjusted via the width of the hysteresis. According to the invention, it is preferred to determine the duty cycle of the PWM signal using a low-pass filter, preferably an RC low-pass filter. PID controllers, for example, can be used as controllers for the battery current or the duty cycle.

[0054] If, for example, a machine tool is to be braked with a comparatively cold and full rechargeable battery («accumulator»), the rechargeable battery initially has a high cell voltage, preferably due to the high battery charge level, and a high internal cell resistance due to the low temperatures. When electrical energy is fed back into the energy supply device, the battery voltage can rise quickly, so that the voltage limit U_Akku, max of the energy supply device is reached within a short time. Within the scope of the proposed braking method, the voltage is advantageously limited to this limit value U_Akku, max. According to the invention, it is preferred that the energy supply device is operated within the range of the voltage limit U_Akku, max over long stretches of the braking process.

[0055] For example, if a machine tool is to be braked with a relatively warm and essentially half-charged battery, the voltage limit U_Battery, max will not be reached. Instead, it may be preferable in this case to actively limit the battery current to the limit value using a control system.

[0056] 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.

[0057] In the figures, identical and similar components are numbered with the same reference numerals.

[0058] They show:

[0059] Fig. 1 Working range of a possible stator current space vector in a space vector representation for efficient generator braking operation

[0060] Fig. 2a, b Working range of a possible stator current space vector in a space vector representation with maximum lossy generator braking operation

[0061] Fig. 3 Possible block diagram of «recuperation» with efficient generator braking operation without brake chopper

[0062] Fig. 4 possible block diagram «recuperation» with efficient generator braking operation with brake chopper

[0063] Fig. 5 Possible block diagram of «recuperation» with maximum lossy generator braking operation without brake chopper

[0064] Fig. 6 Possible block diagram of «recuperation» with maximum lossy generator braking operation with brake chopper

[0065] Fig. 7 schematic plot of speed against time to illustrate the braking and acceleration time

[0066] Fig. 8 schematic plot of speed against time to illustrate the braking and acceleration time

[0067] Fig. 9 schematic representation of a preferred embodiment of the proposed machine tool. Examples of embodiments and description of the figures:

[0068] Figure 1 shows a possible space vector representation depicting the operation of a machine tool 10. In particular, Figure 1 shows the operating range AB of a possible stator current space vector l_S in such a space vector representation during efficient regenerative braking operation of the machine tool 10. The I_d value of the current flowing through the motor 12 of the machine tool 10 is shown on the x-axis of the space vector representation. A machine tool 10 is shown schematically in Fig. 8.

[0069] The y-axis of the space vector representation shows the I_q value of the current flowing through the motor 12 of the machine tool 10. The value l_q represents the torque-generating component of the current, while the value l_d represents the field-generating current component.

[0070] Figure 1 shows the four quadrants 1, 2, 3 and 4 of a space vector representation. The first quadrant 1 is characterized by a negatively increasing torque \ M and generator operation G. The second quadrant 2 is characterized by a positively increasing torque ^M and motor operation M. The third quadrant 3 is characterized by a negatively increasing torque \ M and motor operation M. The fourth quadrant 4 is characterized by a positively increasing torque ^M and generator operation G. The increasing and decreasing torques of the torque hyperbolas are symbolized in Figures 1 and 2 by dashed arrows. The torque hyperbolas are preferably formed by operating points with the same torque. A circle K is drawn in Figure 1, where circle K represents the current limit of an inverter of machine tool 10. Circle K orThe current limit of the inverter lies equally in the four quadrants 1, 2, 3, and 4 of the space vector representation, which means that a center point of the circle K coincides with the intersection point of the y- and x-axes of the space vector representation. The operating range AB of the stator current space vector l_S is shown in the third quadrant 3 of the space vector representation. In the space vector representation shown in Figure 1, the operating range AB of the stator current space vector l_S coincides with the MTPA characteristic curve of the machine tool 10. The motor 12 of the machine tool 10 is therefore advantageously operated at an efficiency-optimized operating point in which the current heat losses are minimal.

[0071] The 0 Nm characteristic curve N runs through the first quadrant 1 and the fourth quadrant 4, essentially parallel to the y-axis of the space vector representation. Furthermore, a second 0 Nm characteristic curve N2 results, which runs on the x-axis or coincides with the x-axis (therefore not shown). The space vector representation depicted in Figure 1 shows a machine tool 10 and its operation, in which the braking power of the machine tool 10 is reduced by determining at least one correction factor k and applying it to a maximum motor current l_S, max of the machine tool 10, so that a reduced setpoint l_S, red for the motor current is obtained. This corresponds to efficient regenerative braking operation of the machine tool 10.

[0072] Figures 2a and 2b show a space vector representation of a maximum-loss generator braking operation of a machine tool 10. In contrast to Figure 1, in the braking method shown in Figure 2, a current space vector l_S, max is rotated in the space vector representation by applying a changed braking angle ß_brems, so that a length of the current space vector l_S, max remains essentially unchanged and the braking power of the machine tool 10 is reduced. The current space vector l_S, max is initially located in the third quadrant 3 of the space vector representation, but as a result of the rotation in Figure 2a, it reaches the boundary between the second quadrant 2 and the third quadrant 3. The current space vector l_S, max is initially located in the third quadrant 3 of the space vector representation, but as a result of the rotation in Figure 2b, it reaches the fourth quadrant 4.The braking angle ß_brems is also shown in the fourth quadrant 4 of the space vector representation. The rotated current space vector l_S, max intersects the circular area K in the fourth quadrant 4, which represents the current limit of the inverter of the electronics of the machine tool 10. This intersection point of the rotated current space vector l_S, max and the circular area K coincides with the intersection point of the circular area K and the 0 Nm characteristic curve N in the exemplary embodiment of the invention shown in Figure 2. The operating range AB is therefore limited to operating points between the states "maximum braking torque" and "no braking torque, i.e., 0 Nm".

[0073] It should be noted that the block diagrams shown in Figures 3 to 6 show exemplary braking methods for a machine tool 10 in which the motor 12 is operated with a field-oriented control. The proposed method can, of course, also be implemented with a machine tool 10 in which the motor 12 is controlled with block commutation. The motor 12 of the machine tool 10 is a brushless motor, which can preferably deliver a power of more than 1,800 watts (W).

[0074] Fig. 3 shows a possible block diagram of "recuperation" with efficient generator-type braking operation of a machine tool 10 without a brake chopper 18. In the braking process shown in Figure 3, the battery voltage regulator 20 is configured to output a correction factor k_U, red for the voltage of the energy supply device 14, while the battery current regulator 22 is configured to output a correction factor kJ, red for the current of the energy supply device 14. In addition, a speed controller 30 is provided which regulates the speed n of the machine tool 10. Setpoint current values ​​are obtained as output or manipulated variables of the braking process and can be passed on to the motor current controllers 34, 36. The setpoint current values ​​can preferably be setpoint current values ​​for the d and q axes of the space vector representation.The motor current controllers 34, 36 represent in particular a d-current controller 34 and a q-current controller 36, wherein the motor current controllers 34, 36 pass their control commands to the pulse width modulation PWM.

[0075] Fig. 4 shows a possible block diagram for "recuperation" with efficient generator-type braking operation of a machine tool 10 with a brake chopper 18. The block diagram shown in Figure 4 shows the battery current controller 22, the speed controller 30, and the motor current controllers 34, 36, which are already known from Figure 3 and the block diagram shown there. Furthermore, Figure 4 shows a duty cycle controller 28, which, within the meaning of the invention, can preferably also be referred to as a "third controller" and is used to limit the duty cycle to a setpoint value D_setpoint of, for example, 95%. The output value of this third controller is a correction factor k_red, which lies between the values ​​0 and 1. This correction factor k_red can be multiplied by the current l_S, max to obtain the reduced motor stator setpoint current l_S, red.

[0076] Furthermore, the block diagram shown in Figure 4 shows a two-point controller 24 with hysteresis, which is preferably referred to as the "first controller" in the sense of the invention. This first controller 24 is preferably used to control the braking resistor 18 referred to as the "brake chopper". The first controller 24 can, for example, be designed as a comparator with switching hysteresis and be set up to compare an intermediate circuit voltage with a reference voltage. The intermediate circuit voltage can preferably also be referred to as the battery voltage u_Akku, while the reference voltage is referred to in Figure 4 as "U_Chopper". The first controller 24 outputs a PWM signal as an output signal, which outputs a high level when the battery voltage is greater than the reference voltage, i.e. u_Akku > u_Chopper. A duty cycle of the PWM signal can, for example, be formed by the low-pass filter 32 shown in Figure 4.In the sense of the invention, it is preferred that values ​​or quantities which vary over time are designated with lower case letters, while constant values ​​or quantities, such as limit values ​​or other predetermined values, are designated with upper case letters. Fig. 5 shows a possible block diagram for “recuperation” with maximum loss-related regenerative braking operation of a machine tool 10 without a brake chopper 18. Similar to the block diagram in Figure 3, the braking method described in Figure 5 outputs correction factors k_U, red and kJ, red which can be combined to form a common correction factor k_red. The correction factor k_red used in Figure 5 preferably results from a combination of the correction factors k_U, red and kJ, red for the voltage and the electrical current.In the embodiment of the invention shown in Figure 5, in which preferably no brake chopper 18 is used, the correction factor k_red has no component that is attributable to a duty cycle of the brake chopper 18.

[0077] In particular, the correction factor k_U, red from the battery voltage regulator 20 and the correction factor kJ, red from the battery current regulator 22 can be determined. From the correction factors k_U, red and kJ, red, the combined correction factor k_red can be calculated, which can be used to calculate the stator current space vector angle or braking angle ß_brems. To do this, the angles ß_brems, MTPA and ß_brems, 0 Nm are subtracted from each other and multiplied by the combined correction factor k_red. The ß_brems, 0 Nm can be added back to the product to obtain the braking angle ß_brems. The parameter ß_brems, MTPA preferably represents the angle on the MTPA characteristic curve, while the parameter ß_brems, 0 Nm corresponds to the stator current space vector angle in the fourth quadrant 4 of the space vector representation or the stator current space vector angle on the x-axis between the second quadrant 2 and the third quadrant 3 at which no torque is generated.This parameter ß_brems, 0 Nm in the fourth quadrant 4 preferably results from the intersection point of the current limit circuit K with the 0 Nm characteristic curve N. With the help of the braking angle ß_brems and the current l_S, max, the d and q setpoints can be calculated, which can be passed on to the d current controller 34 and the q current controller 36.

[0078] Fig. 6 shows a possible block diagram of “recuperation” with maximum loss-prone regenerative braking operation of a machine tool 10 with brake chopper 18, wherein the block diagram shown in Fig. 6 is largely a combination of elements of the block diagrams from Figs. 4 and 5.

[0079] Fig. 7 shows a schematic plot of the speed n of the motor 12 of the machine tool 10 against time t to illustrate the braking time t_down and the acceleration time t_up. A possible curve of the speed n is shown with an interruption between the times t1 and t2. In the time period between the times t0 and t1, the speed n of the machine tool 10 increases in order to reach a maximum value n_max at time t1. This time period between the limits t1 and t2 is referred to in the invention as the acceleration time t_up. From the maximum speed value n_max, the machine tool 10 can be brought to a standstill by a braking process. In conventionally operating machine tools, such a braking process can take place according to the dashed line in Figure ? and, for example, last longer than the acceleration time t_up.In this case, the ratio of deceleration time to acceleration time can be greater than 1 because the deceleration time t_down is greater than the acceleration time t_up. In the plot of speed n versus time t shown in Figure 7, the deceleration time t_down is limited by the times t2 and t3.

[0080] According to a preferred embodiment of the invention, the braking of the machine tool 10 takes place according to the two solid lines in Figure 7. The braking takes place according to a normal braking process according to the right-hand solid line, with a braking time t_down lying in a range between 2 and 4 seconds. In such a case, the ratio of braking time to acceleration time can be less than 1, i.e. the braking time t_down is less than the acceleration time t_up. After a kickback case is detected, the machine tool 10 or its tool 16 can be braked in less than 1.5 seconds. Such a rapid or kickback braking process is represented by the left-hand solid line in Figure 7. In such a case, the ratio of braking time to acceleration time can be less than 0.7, preferably less than 0.5, i.e. the braking time t_down is significantly less than the acceleration time t_up.For example, the braking time t_down can be less than 70%, preferably less than 50% of the acceleration time t_up.

[0081] Figure 8 also shows a schematic plot of the rotational speed n of the motor 12 of the machine tool 10 against time t to illustrate the braking time t_down and the acceleration time t_up. The inventors have recognized that with a reduced rotational speed, the rotating cutting disk 16 has only very little rotational energy and therefore poses little risk to the user of the machine tool 10. It may therefore be sufficient in the context of the invention that the tool 16 of the machine tool 10 is not brought to a complete standstill, but that the braking process ends beforehand, for example when the tool 16 of the machine tool 10 rotates at a rotational speed n of less than 70%, preferably less than 63%, 55%, 45%, 32%, or 22% of the original rotational speed n_max of the tool 16.Of course, the tool 16 of the machine tool 10 can also rotate at an even lower proportion of the original speed n_max until it is decelerated to a standstill, for example. The end of the deceleration time t_down is then determined accordingly by end times t3_70%, t3_63%, t3_55%, t3_45%, t3_32%, or t3_22%. Of course, all intermediate values ​​between 70 and 0% are also possible, such as 67%, 57.5%, 43.33%, 2.56%, etc. In this embodiment of the invention, it is preferred that the greater part of its rotational energy is extracted from the tool 16 of the machine tool 10 and fed back into the energy supply device 14 of the machine tool 10. By removing the majority of the rotational energy, the tool 16 of the machine tool 10 can be braked to such an extent that the rotating cutting disk 16 no longer poses a danger to the user of the machine tool 10.If the braking time t_down does not end when the tool 16 of the machine tool 10 comes to a standstill, but rather already when the tool 16 of the machine tool 10 is only rotating at less than 70%, preferably less than 63%, 55%, 45%, 32%, 22% of the original speed n_max of the tool 16, then the time period until the tool of the machine tool actually comes to a standstill is advantageously no longer important, because the braking time t_down or its end point t3 is determined by reaching the lower speed.

[0082] It may also be preferred in the sense of the invention that the machine tool 10 or its tool 16 is brought to a standstill with a reduced gradient with a different pitch.

[0083] In the plot of speed n against time t shown in Figure 8, constant straight lines are plotted for the values ​​of 90% of the maximum speed n_max and 10% of the maximum speed n_max. The value of 90% of the maximum speed n_max, together with the corresponding time value 11_90%, forms a pair of values ​​that lie on the graph n(t). Analogously, the value of 10% of the maximum speed n_max, together with the corresponding time value t3_10%, forms a pair of values ​​that lie on the graph n(t).

[0084] Figure 9 shows a schematic representation of a preferred embodiment of the proposed machine tool 10. The machine tool 10 has a motor 12, which is preferably designed as a brushless motor. The machine tool 10 can have a tool 16, which can be designed, for example, as a disk-shaped cutting tool. The machine tool 10 shown in Figure 9 is preferably a cut-off machine with which cuts can be made in a substrate, such as concrete. The tool 16 of the machine tool 10 can be surrounded by a blade guard (without reference symbol) to protect the user of the machine tool 10 from flying chips and sparks. The machine tool 10 can be connected to at least one energy supply device 14 to supply the machine tool 10 with electrical energy.Of course, the machine tool 10 can also have two or more energy supply devices 14. In the context of the present invention, electrical energy can be fed back into the at least one energy supply device 14, particularly when the machine tool 10 is decelerated. The machine tool 10 can also have one or more handles (without reference numerals) with which the user of the machine tool 10 can transport the machine tool 10 or guide it during operation.

[0085] List of reference symbols

[0086] 1 1st quadrant of the space vector representation

[0087] 2 2nd quadrant of the space vector representation

[0088] 3 3rd quadrant of the space vector representation

[0089] 4 4th quadrant of the space vector representation

[0090] 10 Machine tool

[0091] 12 Engine

[0092] 14 Power supply device

[0093] 16 tools

[0094] 18 brake choppers

[0095] 20 Voltage regulator of the power supply device

[0096] 22 Current regulator of the power supply device

[0097] 24 first controller

[0098] 26 second controller

[0099] 28 third controller, in particular duty cycle controller

[0100] 30 speed controllers

[0101] 32 low-pass filters

[0102] 34 d-current regulator

[0103] 36 q-current controllers

[0104] M Engine operation

[0105] G Generator operation l_d torque l_q torque

[0106] 'IM positively increasing torque s M negatively increasing torque

[0107] K Circuit range as current limit of the inverter

[0108] AB Working range of the stator current space vector

[0109] N 0 Nm characteristic curve

[0110] MTPA MTPA characteristic curve (Maximum Torque per Ampere or maximum

[0111] Torque per ampere ß_brake Braking angle

[0112] PWM pulse width modulation n speed t time

Claims

Patent claims 1. A method for braking a machine tool (10), wherein the machine tool (10) is a battery-operated machine tool and electrical energy released during braking of the machine tool (10) is fed back into a power supply device (14) of the machine tool (10), characterized by the following method steps: a) operating the machine tool (10) under specification of a first current value, b) feeding back the electrical energy released during braking of the machine tool (10) into the power supply device (14) of the machine tool (10), c) reducing a braking power of the machine tool (10) if at least one limit value of the power supply device (14) is exceeded, d) continuing to operate the machine tool (10) with target current values, wherein the target current values ​​are calculated based on the reduction in the braking power of the machine tool (10) and the first current value.

2. Method according to claim 1, characterized in that the machine tool (10) is operated along a power loss-optimized characteristic curve.

3. Method according to claim 1 or 2, characterized in that the machine tool (10) is operated along an MTPA characteristic curve in a space vector representation.

4. Method according to claim 3, characterized in that the target current values ​​are target current values ​​for the d- and q-axes of the space vector representation.

5. Method according to one of the preceding claims, characterized in that the braking power of the machine tool (10) is reduced by the following method step: e) rotation of a current space vector l_S, max in the space vector representation by applying a changed braking angle ß_brems, so that a length of the current space vector l_S, max remains essentially unchanged.

6. Method according to one of claims 1 to 4, characterized in that the braking power of the machine tool (10) is reduced by the following method steps: f) determining at least one correction factor k and g) applying the at least one correction factor k to a maximum motor current l_S, max, whereby a reduced setpoint value l_S, red for the motor current is obtained.

7. Method according to claim 6, characterized in that the at least one correction factor k lies in a value range between 0 and 1.

8. The method according to claim 6 or 7, characterized in that the at least one correction factor k is composed of a first correction factor k_U, red, a second correction factor kJ, red and / or a third correction factor k_red, wherein the first correction factor k_U, red is determined by a voltage regulator of the energy supply device and the second correction factor kJ, red is determined by a current regulator of the energy supply device and the third correction factor k_red is used to limit a duty cycle.

9. Method according to one of the preceding claims, characterized in that the machine tool (10) comprises a brake chopper (18), wherein electrical energy released during braking of the tool (16) of the machine tool (10) is picked up by the brake chopper (18).

10. Method according to one of the preceding claims, characterized in that a control of a motor (12) of the machine tool (10) comprises a field-oriented control or a block commutation.

11. Method according to one of the preceding claims, characterized in that the tool (16) of the machine tool (10) is stopped with a braking time in a range of 2 to 4 seconds.

12. Method according to one of the preceding claims, characterized in that the tool (16) of the machine tool (10) is braked with a braking time of less than 1.5 seconds, preferably less than 1 second, most preferably less than 0.5 seconds, if braking occurs after detection of a kickback event.

13. Method according to one of the preceding claims, characterized in that a ratio of braking time t_down to acceleration time t_up is less than 1.

14. Machine tool (10) for carrying out the method according to one of the preceding claims, characterized in that a motor (12) of the machine tool (10) is a brushless motor.

15. Machine tool (10) according to claim 14, characterized in that the machine tool (10) comprises a brake chopper (18), wherein the brake chopper (18) is designed to absorb electrical energy which is released when the tool (16) of the machine tool (10) is braked.

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