MACHINE TOOL WITH A BRUSHLESS MOTOR AND METHOD FOR CONTROLLING A MACHINE TOOL

Description

[0001] The invention relates to a machine tool comprising a brushless motor and power electronics, wherein the power electronics have at least one H-bridge circuit via which the motor is supplied with energy.

[0002] Some motor control methods provide for periodic measurement of an operating parameter of the motor. For this purpose, the power electronics may include at least one measuring resistor. The measuring resistor may be arranged in a supply line of the H-bridge circuit.

[0003] DE 10 2018 124589 A1 describes an energization device for reducing an excitation coil magnetic field.

[0004] WO 2020 / 085507 A1 describes a power tool with a brushless motor. A control means of the power tool may include a lead angle control section for controlling a lead angle of the brushless motor.

[0005] The object of the present invention is to provide a machine tool and a method for controlling a machine tool according to claim 1 and claim 5, respectively, which make it possible to measure an operating parameter required for controlling the motor precisely and cost-effectively.

[0006] The object is achieved by a machine tool comprising a brushless motor and power electronics, wherein the power electronics have at least one H-bridge circuit via which the motor is supplied with energy, wherein at least one measuring resistor is arranged in a supply line of the H-bridge circuit, wherein the power electronics are configured to switch the H-bridge circuit crosswise.

[0007] The H-bridge circuit can have at least four switches. The switches can be and / or comprise power semiconductors, such as FET transistors, such as MOS-FETs. One of the switches can be provided in each of the four branches of the H-bridge circuit.

[0008] The motor can be arranged in the bridge branch of the H-bridge circuit. The H-bridge circuit can have a first and a second supply line. Two of the four branches can be connected to one of the two supply lines.

[0009] Then, in one variant, a cross-connection of the H-bridge circuit can be understood as a connection of the four switches in which a first switch in a first branch, which is connected to the first supply line, and a fourth switch in a fourth branch, which is connected to the second supply line, are initially closed. A second and a third switch, each located in one of the two remaining branches, in particular a second and a third branch, can be open.

[0010] Likewise, a second variant can correspond to a cross-connection if the second switch in the second branch, which is connected to the second supply line, and the third switch, which is connected in a third branch, which is connected to the first supply line, are switched and the first and fourth switches are open.

[0011] Thus, for a cross-connection, the first and fourth or the second and third switches can be switched and the other switches can be open.

[0012] The first variant and the second variant can in particular be switched periodically and alternately.

[0013] The measuring resistor is located in one lead of the H-bridge circuit. For example, the measuring resistor can be located in the second lead.

[0014] By cross-connecting the H-bridge circuit, it can be achieved that the measuring resistor is energized during at least a predominant part of a switching period of the H-bridge circuit when the motor is periodically controlled.

[0015] This allows an electrical parameter of the measuring resistor, such as a voltage drop across it, to be measured during a relatively long measurement window within each switching period. The measured parameter can then be used to determine an operating parameter of the motor. For example, the voltage drop in conjunction with the resistance of the measuring resistor can be used to determine the current flowing through it and thus also the current flowing through the motor.

[0016] Since the measurement window is relatively long, a measurement can alternatively or additionally begin with a time offset from the beginning of a switching period. The time offset can be chosen such that transient phenomena or similar phenomena have decayed. This can further improve the measurement accuracy.

[0017] Since only a measuring resistor arranged in the supply line is required, production is cost-effective.

[0018] Due to its arrangement in the supply line, the measuring resistor is continuously connected to a defined potential with at least one of its two terminals.

[0019] The cross-connection of the H-bridge circuit does not require a freewheeling phase of the motor.

[0020] Improving measurement accuracy can be particularly effective when the motor is capable of and / or intended to generate high power. For example, the motor may have a maximum power of at least 1 kW, or at least 3 kW, for example. The maximum power may be a peak power and / or a continuous power, measured, for example, over at least 60 seconds.

[0021] The motor can have multiple coils. The coils can be controlled and / or driven via multiple H-bridge circuits. For this purpose, the power electronics can have multiple, in particular at least three, H-bridge circuits.

[0022] The machine tool can be designed as a mobile machine tool. For this purpose, it can be designed, for example, as an electric handheld power tool and / or comprise such a tool.

[0023] Alternatively or additionally, the machine tool, in particular the mobile machine tool, can also be designed as a construction robot and / or comprise such a robot.

[0024] The machine tool can be configured for use on a construction site, for example, a building construction site and / or a civil engineering site. It can be designed for drilling, cutting, for example, chiseling, sawing or cutting, pressing, and / or grinding. Accordingly, the machine tool can be configured to accommodate a tool, for example, a drilling tool, a cutting tool, for example, a chiseling tool, a saw blade or a knife, a pressing tool, or a grinding tool, for example, a grinding wheel.

[0025] Alternatively or additionally, it is conceivable that the machine tool is configured for suction, blowing, and / or measuring. Accordingly, it can be configured to accommodate a tool in the form of a suction and / or blowing tool, for example, a suction and / or blowing pipe, and / or a measuring tool.

[0026] The machine tool, in particular the mobile machine tool, can be portable. It can therefore have a weight of no more than 43 kg, particularly preferably no more than 25 kg, in particular no more than 10 kg, for example no more than 5 kg. The machine tool can, for example, be an electric handheld power tool.

[0027] "Mobile" can also include a machine tool that is designed to be temporarily fixed to a surface, for example, to perform construction work. This can also include column-mounted handheld power tools, for example.

[0028] Alternatively or in addition to portability, the machine tool, in particular the mobile machine tool, may have a mobile platform. The mobile platform may have a chassis, for example a tracked chassis and / or a wheeled chassis.

[0029] In particular, the machine tool can also be designed as a construction robot. For this purpose, it can have a manipulator. An end effector can be arranged and / or formed on the manipulator. The end effector can be configured to directly and / or indirectly pick up the tool. For example, the machine tool can be designed as a drilling construction robot, a chisel construction robot, and / or a grinding construction robot.

[0030] The scope of the invention also includes a method for controlling a machine tool with the features described above.

[0031] The H-bridge circuit of the machine tool is switched crosswise and periodically.

[0032] The measuring resistor arranged in the supply line of the H-bridge circuit can thus be subjected to current over a relatively long period of time within a switching period.

[0033] Thus, the electrical parameter can be determined over a large portion of the switching period.

[0034] A measurement on the measuring resistor can also be performed with a time delay from the beginning of a switching period. This allows, for example, a measurement to begin after transient phenomena or similar processes have, at least largely, subsided.

[0035] Due to the small number of measuring resistors required, a cost advantage can arise.

[0036] An electrical parameter can be measured at the measuring resistor during at least one measurement window. The electrical parameter can be, for example, a voltage drop across the measuring resistor. The voltage drop can correlate with an operating parameter of the motor, such as a current flow through the motor, particularly when the resistance value of the measuring resistor is constant or essentially constant. Thus, the operating parameter of the motor can be determined based on the electrical parameter measured at the measuring resistor.

[0037] The measurement window may comprise a measurement duration of at least 50% of the switching period of the H-bridge circuit.

[0038] If multiple measurement windows are available within a switching period of the H-bridge circuit, a longest measurement window can be selected for measuring the electrical parameter. Alternatively or additionally, if multiple measurements of the electrical parameter are performed during different measurement windows within the switching period, the measurement from the longest measurement window can be used.

[0039] If the measurement is based on summing or averaging several individual measured values ​​within a measurement window, a longer measurement window can better compensate for random fluctuations. This also improves the achievable measurement accuracy.

[0040] Further features and advantages of the invention will become apparent from the following detailed description of exemplary embodiments of the invention, based on the figures of the drawing, which illustrate details essential to the invention, and from the claims. The features shown therein are not necessarily to scale and are presented in such a way that the special features of the invention can be clearly seen. The various features can be implemented individually or in combinations in variants of the invention.

[0041] The schematic drawing shows embodiments of the invention and explains them in more detail in the following description.

[0042] They show: Fig. 1 a machine tool in the form of an electric hand-held power tool; Fig. 2 a machine tool in the form of a construction robot; Figs. 3 and 4Circuit diagrams of a power electronics system with an H-bridge circuit; Fig. 5 a time diagram of the states of two switches and of time periods of possible measurement windows; and Fig. 6 a block diagram of a power electronics system with several H-bridge circuits.

[0043] In the following description of the figures, the same reference numerals are used for identical or functionally corresponding elements to facilitate understanding of the invention.

[0044] Fig. 1 shows a machine tool 100. The machine tool 100 comprises a drilling machine tool 102. This is designed as an electro-pneumatic hammer drill. It has a tool holder 104 in which a rock drilling tool 105 The machine tool 100 is designed for drilling reinforced rock.

[0045] Furthermore, the machine tool 100 has a grip area106 The grip area 106 is designed for manual and / or mechanical holding of the machine tool 100.

[0046] Between the handle area 106 and the rest of the machine tool 100, a vibration damping 108 designed to minimize transmission of vibrations from the rest of the machine tool 100 to the handle area 106.

[0047] Furthermore, the drilling device 100 has a suction device 110 The suction device 110 is arranged, in particular detachably, on the machine tool 100. It is configured to selectively generate an air flow through negative pressure or positive pressure. Thus, it can be operated selectively as a suction device or as a blowing device.

[0048] The drilling machine 102 and the suction device 110 are powered by a battery pack 112 supplied with electrical energy.

[0049] The drilling machine tool 102, and thus the machine tool 100, further comprises power electronics 50 on.

[0050] The power electronics 50 is electrically connected to a motor M1 connected. Motor M1 is a brushless motor. It is configured to drive tool 105. Power electronics 50 is configured to control motor M1.

[0051] The power electronics 50 and the motor M1 are arranged within the drilling machine 102. For illustration purposes, they are shown in Fig. 1 only shown schematically.

[0052] It is conceivable that the suction device 110 also has a brushless motor which is controlled by a power electronics of the suction device 110 corresponding to the power electronics 50.

[0053] Fig. 2 shows a machine tool 101.Machine tool 101 is designed as a drilling robot. It has a mobile platform 116 The mobile platform 116 is designed, for example, as a tracked vehicle. The mobile platform 116 can be remotely controllable, semi-autonomous, and / or fully autonomous.

[0054] On the mobile platform 116 there is a lifting device 118 arranged through which a manipulator 120 can also be displaced vertically. The manipulator 120 is designed in the form of an arm. It has six degrees of freedom.

[0055] At its free end, the manipulator 120 has a machine tool holder 122. A machine tool 100 is accommodated in the machine tool holder 122. The machine tool 100 can be used as described above in connection with Fig. 1 described embodiment.

[0056] Fig. 3 and Fig. 4show simplified circuit diagrams of a power electronics 50 with an H-bridge circuit 10. The power electronics 50 can be the power electronics 50 of the embodiments according to Fig. 1 and Fig. 2 are equivalent to.

[0057] The H-bridge circuit 10 has a total of four switches S1, S2, S3, S4 on.

[0058] The switches S1, S2, S3, and S4 can be power semiconductors, for example. They can be transistors and / or comprise them. Two of the switches S1, S2 and S3, S4 are connected in series with each other and in parallel with the other two switches S3, S4 and S1, S2, respectively.

[0059] Each of the switches S1, S2, S3, S4 is connected to one of four branches of the H-bridge circuit 10.

[0060] The H-bridge circuit 10 is supplied with energy via a first and a second supply line 12, 14. In one of the two supply lines 12, 14,for example in the second supply line 14, a measuring resistor R1 switched on.

[0061] Its voltage drop can be measured using 2 measuring points 16, 18 measured. Motor M1 is connected in the bridge arm of the H-bridge circuit 10. Motor M1 is again a brushless motor.

[0062] Figs. 3 and 4 show two phases within a switching period that drive motor M1. The H-bridge circuit is connected crosswise for this purpose.

[0063] In a first phase, as described in Fig. 3As shown, switches S1 and S4 are switched on, while switches S2 and S3 are open. Current can thus flow, for example, from the first supply line 12 via switch S1 and motor M1, as well as switch S4, to the second supply line 14. Current flows through the measuring resistor R1 during this phase. A voltage drop, in particular proportional to the current flowing through the measuring resistor R1, can be measured at measuring points 16, 18.

[0064] In a second phase within the switching period, as in Fig. 4 As shown, switches S1 and S4 are open. Now switches S2 and S3 are closed.

[0065] In this second phase, current can flow, for example, from the second supply line 14 via the measuring resistor R1, the switch S2, and the motor M1, and then via the switch S3 to the first supply line 12. Current also flows through the measuring resistor R1 during this phase. Thus, a voltage drop proportional to the current flow through the measuring resistor R1 can be measured at measuring points 16, 18 during this phase as well.

[0066] Such a cross connection of the switches S1, S2, S3, S4, especially with the two different phases as in Fig. 3 and Fig. 4 shown, can now be repeated afterwards.

[0067] The direction of the current flow, in particular from the first supply line 12 to the second supply line 14 or vice versa, can be adjusted by adjusting the potentials at terminals of the supply lines 12, 14.

[0068] The switches S1, S2, S3, S4 can be controlled by a control unit of the power electronics 50. The control unit can comprise, for example, a microcontroller. The microcontroller can comprise a microprocessor, a memory unit with an executable program code stored therein, as well as control outputs. The program code can be configured to switch the H-bridge circuit 10 crosswise when executed on the microcontroller. In particular, it can be configured to switch the H-bridge circuit 10 periodically and alternately according to the two phases according to Fig. 3 and Fig. 4 to switch.

[0069] Fig. 5 shows a timing diagram of the power electronics 50 and the H-bridge circuit 10 from Fig. 3 and Fig. 4 over a switching period TP.As an example, the switching states of the two switches S1 and S3 are plotted over time. The value 1 corresponds to a closed switch, while the value 0 corresponds to an open switch. These states also correspond to current flows through the respective switches S1 and S3.

[0070] The third graph shows the current flow through the measuring resistor R1, simplified to two levels. A value of 1 indicates that current is flowing through the measuring resistor R1, while a value of 0 means that no current, or at least a negligible current, is flowing through the measuring resistor R1.

[0071] It can be seen that switches S1 and S3 operate in opposite directions. Thus, exactly one of the two switches S1 or S3 is always switched on, while the other switch S3 or S1 is open.

[0072] Current flows through the measuring resistor R1 at almost any time. An exception is a short switching period dTU, during which the switches S1 and S3, and in particular also the switches S2 and S4, each change their switching state.

[0073] Thus, a measurement of an electrical parameter, for example the voltage drop across the measuring resistor R1 within the switching period TP during two measuring windows W1, W2 It can be seen that the two measurement windows W1, W2 together cover significantly more than 50 percent of the switching period TP.

[0074] The duty cycle, in particular the ratio of the duration of the first phase ( Fig. 3 ) to the duration of the second phase ( Fig. 4) can be varied. Thus, one of the two measurement windows W1, W2 can be longer than the other. If the two measurement windows W1, W2 are of equal length, a measurement of an electrical parameter of the measuring resistor R1 can be performed in one of the two measurement windows W1, W2 or in both measurement windows W1, W2. In the latter case, for example, an average value can be calculated from the results of the individual measurements in the individual measurement windows W1 or W2.

[0075] For example, the timeline according to Fig. 5 It is assumed that a measurement is taken during the second measurement window W2.

[0076] In order to avoid incorrect measurements due to transient processes or the like, a transient time period can be set after the start of the measuring window W2, for example after an edge of the voltage drop measured at the measuring resistor R1. dTEAfter the settling time dTE has elapsed, the actual measurement can be carried out over a period of time dTM across.

[0077] Individual measured values ​​during this measuring period dTM can, for example, be averaged in order to obtain a measured value of the electrical parameter of the measuring resistor R1 that can also be used for other purposes.

[0078] Fig. 6 now shows a block diagram of another embodiment of a power electronics 50.

[0079] The power electronics 50 has several, in particular for example three, H- Bridge circuits 10. The H-bridge circuits 10 can, at least substantially, correspond to the H-bridge circuit 10 as described above.

[0080] In the power electronics 50, the individual H-bridge circuits 10 are each connected to different coil circuits of motor M1. Their respective switching periods can be offset from one another. The time offset can be selected such that the smoothest, for example, even, running of motor M1 is achieved. List of reference symbols

[0081] 10Bridge circuit 12Supply line 14Supply line 16Measuring point 18Measuring point 50Power electronics 100Machine tool 101Machine tool 102Drilling machine 104Tool holder 105Rock drilling tool 106Grip area 108Vibration damping 110Suction device 112Battery pack 116Platform 118Lifting device 120Manipulator M1Motor R1Measuring resistor S1Switch S2Switch S3Switch S4Switch TPSwitching period W1Measuring window W2Measuring window dTEDuration dTMDuration dTUSwitching period

Claims

1. Power tool (100, 101), comprising - a brushless motor (M1) and - a power electronics system (50), wherein the power electronics system (50) has at least one H-bridge circuit (10), via which the motor (M1) is supplied with power, - wherein at least one measuring resistor (R1) is arranged in a feed line (12, 14) of the H-bridge circuit (10), - wherein the power electronics system (50) is configured to switch the H-bridge circuit (10) crosswise, characterized in that the power tool (100, 101) is configured to measure an electrical parameter at the measuring resistor (R1) during at least one measuring window (W1, W2), wherein, when there are several measuring windows (W1, W2) within one switching period (TP) for the switching of the H-bridge circuit (10), the longest measuring window (W1, W2) is selected for measuring the electrical parameter and / or wherein, when the electrical parameter is measured several times during different measuring windows (W1, W2) within the switching period (TP), the measurement that originates from the longest measuring window (W1, W2) is used further.

2. Power tool according to the preceding claim, characterized in that the power electronics system (50) has a plurality of, in particular at least three, H-bridge circuits (10).

3. Power tool according to either of the preceding claims, characterized in that the power tool (100, 101) is in the form of an electric handheld power tool and / or comprises such an electric handheld power tool.

4. Power tool according to one of the preceding claims, characterized in that the power tool (100, 101) is in the form of a construction robot and / or comprises such a construction robot.

5. Method for controlling a power tool (100, 101), comprising a brushless motor (M1) and a power electronics system (50), wherein the power electronics system (50) has at least one H-bridge circuit (10), via which the motor (M1) is supplied with power, wherein at least one measuring resistor (R1) is arranged in a feed line (12, 14) of the H-bridge circuit (10), wherein the power electronics system (50) is configured to switch the H-bridge circuit (10) crosswise, wherein the H-bridge circuit (10) is switched crosswise and periodically, wherein an electrical parameter is measured at the measuring resistor (R1) during at least one measuring window (W1, W2), characterized in that, when there are several measuring windows (W1, W2) within one switching period (TP) for the switching of the H-bridge circuit (10), the longest measuring window (W1, W2) is selected for measuring the electrical parameter and / or in that, when the electrical parameter is measured several times during different measuring windows (W1, W2) within the switching period (TP), the measurement that originates from the longest measuring window (W1, W2) is used further.

6. Method according to Claim 5, characterized in that the measuring window (W1, W2) covers a time period of at least 50% of the switching period TP for the switching of the H-bridge circuit (10).