Current measurement circuit, worktable device, and control method for an actuator

Abstract

The present invention provides a current measurement circuit capable of suppressing noise generated in a current path to be measured. A plurality of current sensors are inserted into the current path, the relationship between the current flowing through the current path and the sensor output of each of the plurality of current sensors is different, and the plurality of current sensors are connected in series with each other. A selection circuit selects one sensor output from among the plurality of sensor outputs based on the sensor output from each of the plurality of current sensors, and outputs the selected sensor output as a current measurement value.

Description

[0001] This application claims priority to Japanese Patent Application No. 2024-216268, filed on December 11, 2024. The entire contents of that Japanese application are incorporated herein by reference. Technical Field

[0002] This invention relates to a current measuring circuit, a workbench device, and a control method for an actuator. Background Technology

[0003] A known circuit (Patent Document 1) switches between two current detection units and detects the current based on the magnitude of the current flowing through the path of the current to be measured. The current detection unit for detecting small currents detects the current flowing through a current detection transistor, which is connected in parallel with a transistor that allows current to flow through the current path. The current detection unit for detecting large currents is connected in series with the transistor that allows current to flow through the current path, directly detecting the current flowing through the current path. When detecting small currents, losses caused by the current detection units are reduced by turning on the switch connected in parallel with the current detection unit for large currents.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2013-152181 Summary of the Invention

[0005] In the circuit described in Patent Document 1, the switch is turned on and off during high-current and low-current measurements, thus the noise generated during the switching action is superimposed on the current. The object of this invention is to provide a current measurement circuit capable of suppressing noise generated in the path of the current being measured. Another object of this invention is to provide a control method using this current measurement circuit to control an actuator.

[0006] According to one aspect of the present invention, a current measuring circuit is provided, comprising:

[0007] Multiple current sensors are inserted into a current path, the current flowing through the current path having different relationships with the sensor outputs, and are connected in series;

[0008] The selection circuit selects one sensor output from multiple current sensors based on their respective sensor outputs and outputs the selected sensor output as the current measurement value.

[0009] According to another aspect of the present invention, a worktable apparatus is provided, comprising:

[0010] The current measurement circuit;

[0011] Movable worktable;

[0012] An actuator, driven by an inverter, moves the movable worktable; and

[0013] The driver controls the inverter based on the output from the current measurement circuit.

[0014] According to another aspect of the present invention, a control method is provided, which performs the following processing:

[0015] Multiple current sensors are used to measure the current flowing through the current path. The multiple current sensors are connected in series in the current path, and the relationship between the current flowing through the current path and the sensor output is different for each of them.

[0016] Based on the respective sensor outputs of the plurality of current sensors, one sensor output is selected from the plurality of sensor outputs, and the actuator is controlled according to the selected sensor output.

[0017] Invention Effects

[0018] Because multiple current sensors are connected in series and inserted into the current path, the current flowing through the current path always flows through multiple current sensors, and sensor outputs are always obtained from multiple current sensors. Since the selection circuit selects one of the multiple sensor outputs, the selection has no effect on the current path. Therefore, noise generated in the current path under test can be suppressed. Attached Figure Description

[0019] Figure 1 This is a block diagram of the current measurement circuit 10 based on the first embodiment.

[0020] Figure 2 This is an example showing the relationship between the current Io flowing through the current path 50 and the output voltage Vo of the current sensing elements 12H and 12L, and a graph showing the relationship between the current sensor selected by the selection circuit 15 and the current Io.

[0021] Figure 3 This is a graph illustrating an example of the relationship between current Io and digitally converted output voltage Vo.

[0022] Figure 4 This is a block diagram of a workbench device based on the second embodiment.

[0023] Figure 5 This is a flowchart showing the control steps of motor 21.

[0024] In the diagram: 10, 10U, 10V, 10W - Current measurement circuit; 11H - Current sensor for high current; 11L - Current sensor for low current; 12H, 12L - Current detection element; 13H, 13L - AD converter; 15 - Selection circuit; 20 - Inverter; 21 - Motor; 22 - AC power supply; 23 - Rectifier circuit; 24 - Smoothing capacitor; 25 - Movable worktable; 30 - Driver; 31 - Upper controller; 50, 50U, 50V, 50W - Current path. Detailed Implementation

[0025] refer to Figures 1-3 The current measurement circuit based on the first embodiment will be described.

[0026] Figure 1 This is a block diagram of the current measurement circuit 10 based on the first embodiment. The current measurement circuit 10 includes two current sensors 11H and 11L and a selection circuit 15. The two current sensors 11H and 11L are connected in series and inserted into the current path 50 through which current flows. (See reference...) Figure 2 As explained, the relationship between the current flowing through current path 50 and the sensor output differs between the two current sensors 11H and 11L. One current sensor 11H is a high-current sensor (used for high-current applications), while the other current sensor 11L is a low-current sensor (used for low-current applications).

[0027] The high-current sensor 11H includes a current sensing element 12H and an AD converter 13H, while the low-current sensor 11L includes a current sensing element 12L and an AD converter 13L. The current sensing elements 12H and 12L each output a voltage corresponding to the current flowing through the current path 50. Hall effect elements can be used, for example, as the current sensing elements 12H and 12L.

[0028] A / D converters 13H and 13L convert the voltages (analog signals) output from current sensing elements 12H and 12L into digital signals, respectively. The digital signal converted by the A / D converter is called the "sensor output". The resolution and full-scale voltage value are different between the two A / D converters 13H and 13L.

[0029] The selection circuit 15 selects one sensor output from the current sensors 11H and 11L based on their respective outputs, and outputs the selected sensor output as the current measurement value. The selection circuit 15 can be constructed, for example, using an FPGA (Field Programmable Gate Array). Compared to a system constructed with a CPU and software, the selection circuit 15, constructed with an FPGA, allows for high-speed processing.

[0030] Next, refer to Figure 2 For the two current sensing elements 12H and 12L ( Figure 1 The input and output characteristics of ) will be explained. Figure 2 This indicates that the current flows through a path of 50 ( Figure 1 An example of the relationship between the current Io of the current sensing elements 12H and 12L and the output voltage Vo of the selection circuit 15. Figure 1 The graph shows the relationship between the selected current sensor and the current Io. The horizontal axis represents the current Io, the vertical axis of the upper graph represents the output voltage Vo of the current sensing elements 12H and 12L, and the vertical axis of the lower graph represents the difference between the current sensors 11H and 11L.

[0031] The solid line in the upper chart represents the input-output characteristics C of the high-current sensing element 12H. H The thick solid line represents the input-output characteristics C of the 12L current sensing element for small current applications. L Input / output characteristics C H C L It is point-symmetric with respect to the origin O. The linear characteristic range R of the high-current sensing element 12H is... H The linear characteristic range R of the 12L current sensing element for small current applications L Wide. This extends the linear characteristic range R. H R L The maximum values ​​are respectively labeled as I H I L .

[0032] Since the two current sensors 11H and 11L are connected in series and inserted into the current path 50, the same current flows through the two current sensing elements 12H and 12L. That is, the current flowing through the small current sensing element 12L is the same as the current flowing through the large current sensing element 12H. Therefore, the linear characteristic range R of the small current sensing element 12L with a current rating greater than or equal to that of the large current sensing element 12H is used. H Maximum current I H The component. However, if the current Io exceeds the linear characteristic range R... L Maximum current I L If the current is low, the output of the 12L current sensing element will saturate.

[0033] The detection error Err of the 12H current sensing element for high current applications H The detection error Err of the 12L current sensing element for small currents is greater than that of small currents. L .exist Figure 2 In the diagram, the detection error Err is represented by a dashed line. H Err LOne example within that range. Additionally, in Figure 2 In the middle, the detection error Err H Err L The range is expressed as an enlargement compared to the actual range.

[0034] The selection circuit 15 uses the output of the high-current sensor 11H to provisionally determine the current value of Io. When the provisional current value is within the linear characteristic range R... L When the current Io increases, and the provisional current value exceeds the linear characteristic range R of the low-current sensor 11L, the selection circuit 15 selects the sensor output of the low-current sensor 11L. L The maximum value I L If the selected current sensor Io decreases and the provisional current value falls below the switching threshold I1, then the selection circuit 15 switches the selected current sensor from the high-current current sensor 11H to the low-current current sensor 11L. The switching threshold I1 is set to a value greater than the linear characteristic range R. L The maximum value IL is small. Thus, it imparts a hysteresis characteristic in the timing of current switching.

[0035] When the current Io is small, a small-current current sensor 11L is selected, thus reducing the detection error compared to using a large-current current sensor 11H for current measurement. Furthermore, if the current Io exceeds the linear characteristic range R of the small-current current sensor 11L... L Therefore, a high-current current sensor 11H is selected, which can measure current Io while maintaining linearity.

[0036] Next, refer to Figure 3 The relationship between the output voltage Vo and the current Io, which are converted into digital signals, is explained. Figure 3 This is a graph illustrating an example of the relationship between the current Io and the digitally converted output voltage Vo. When the voltage (analog signal) output from the current sensing elements 12H and 12L is converted into a digital signal by the AD converters 13H and 13L, quantization error occurs. Due to this quantization error, the output voltage Vo varies in a step-like manner relative to the current Io. Furthermore, in Figure 3 In this context, the quantization error is represented as an amplified version of the actual quantization error.

[0037] The full-scale range of the 11L current sensor and the 13L AD converter for low current applications is based on the equivalent linear characteristic range R. L The maximum value of the current I L Output voltage V when current flows through LTo set. The full-scale range of the AD converter 13H of the current sensor 11H for high current is based on the equivalent linear characteristic range R. H The maximum value of the current I H Output voltage V when current flows through H The quantization error is set accordingly. The A / D converter 13L, used as the current sensor 11L for low current applications, employs a component with higher resolution than the A / D converter 13H used for high current applications, in the range of output voltage VL or below. Therefore, compared to using only the high current sensor 11H to measure current, the quantization error is reduced.

[0038] Next, the superior effects of the first embodiment will be explained.

[0039] In the first embodiment, by using a high-current sensor 11H and a low-current sensor 11L, the current measurement range can be expanded and the detection error in the low-current region can be reduced (equivalent to...). Figure 2 Detection error Err L Err H and Figure 3 (The quantization error shown). Furthermore, it is possible to reduce the quantization error in the low-current region.

[0040] Because the two current sensors 11H and 11L, which are connected in series in the current path 50, are connected in series with each other, the current Io is always measured by the two current sensors 11H and 11L. When the current Io crosses a small current range, the linear characteristic range R is used. L Maximum current I L When the threshold I1 changes, and the selected sensor output switches between the two current sensors 11H and 11L, the current path 50 ( Figure 1 It is unaffected by any switching. Therefore, it can prevent noise from being generated during switching.

[0041] In the first embodiment, Hall elements are used in the current sensing elements 12L and 12H. In the Hall element, an isolation amplifier detects and outputs the voltage generated by the Hall effect, thus isolating the path of the current under test (primary circuit) from the output terminal (secondary circuit) that outputs the measurement result. This ensures high safety. Furthermore, even when a large current flows through the path of the current under test, although a Hall element for small currents is used in the nonlinear region, it is possible to select an element whose specifications allow the current to fall within the rated range even in the nonlinear region. Moreover, in the Hall element for current sensing, a constant magnetic field is applied to the current path, which is made of semiconductor, and the magnetic field does not change according to the magnitude of the current. Therefore, magnetic saturation caused by the properties of magnetic materials does not occur.

[0042] Next, a variation of the first embodiment will be described.

[0043] In the first embodiment, in the current path 50 ( Figure 1 Two current sensors 11H and 11L connected in series are inserted into the device, but three or more current sensors connected in series can also be inserted. Furthermore, in the first embodiment, Hall elements are used as current sensing elements 12H and 12L, but other current sensing elements that output a voltage corresponding to the current quantity can also be used.

[0044] For example, as a current sensing element 12L for low current applications, it can be designed to detect the maximum current ( Figure 2 Current I H A current transformer that does not experience magnetic saturation at maximum current ( ), used as a high-current sensing element 12H, can utilize a shunt resistor. This is achieved by designing the low-current sensing element 12L to withstand the maximum current ( ). Figure 2 Current I H Magnetic saturation does not occur even when the current is from a large current (greater than 1000 ohms). Figure 2 Current I L The current rapidly transitions from a large current to a small current (less than) Figure 2 Current I L In the case of a low-inductance current (where the current is low), the current transitions within a range where magnetic saturation does not occur. Therefore, compared to the case where the transition occurs from a state of magnetic saturation (low inductance state) in the current sensing element 12L to a state where magnetic saturation does not occur, the decrease in the accuracy of current value reading can be suppressed. Furthermore, two current transformers with different numbers of turns in the secondary winding can be used as the low-current sensing element 12L and the high-current sensing element 12H.

[0045] In the first embodiment, as Figure 2 As shown, the linear characteristic range R of the current sensing element 12L for small current applications is... L In the current sensing element 12H for high current and 12L for low current, the relationship between current Io and output voltage Vo is the same. As for other structures, the linear characteristic range R of the low current sensing element 12L is... L In this context, the relationship between current Io and output voltage Vo can differ between the high-current sensing element 12H and the low-current sensing element 12L. For example, the following element can be used: for the same current Io, the output voltage Vo of the low-current sensing element 12L is higher than the output voltage Vo of the high-current sensing element 12H.

[0046] As in the modified example of the first embodiment described above, when current transformers are used as current sensing elements 12L and 12H, it is essential to ensure that magnetic saturation does not occur even at high currents. To prevent magnetic saturation at high currents, the size of the magnetic material must be increased, thus the element size increases according to the rated maximum current. In contrast, when using Hall elements, as described above, there is the advantage of not experiencing magnetic saturation.

[0047] Furthermore, when shunt resistors are used for the current sensing elements 12L and 12H, the primary and secondary circuits are not isolated. Therefore, to ensure sufficient safety, it is preferable to insert an insulating IC at the end. Moreover, since large currents also flow through the shunt resistors used for small currents, abnormal heating may sometimes occur, leading to damage to the small current shunt resistors. As described above, when using Hall effect sensors, the primary and secondary circuits are isolated, thus ensuring sufficient safety. Furthermore, as described above, as a small current Hall effect sensor, a component that is designed to withstand large currents without damage can be used.

[0048] As stated above, from the viewpoints of magnetic saturation and component damage, Hall elements are preferred over current transformers or shunt resistors when using current sensing elements 12L and 12H.

[0049] Next, refer to Figure 4 and Figure 5 The workbench apparatus and control method based on the second embodiment will be described.

[0050] Figure 4 This is a block diagram of the workbench apparatus based on the second embodiment. DC current is supplied to the inverter 20 from the AC power supply 22 via the rectifier circuit 23. A smoothing capacitor 24 is connected between the high-voltage side power line and the low-voltage side power line of the inverter 20. The inverter 20 includes a high-voltage side switching element Q for phase U. UH and low-voltage side switching element Q UL V-phase high-voltage side switching element Q VH and low-voltage side switching element Q VL Phase W high-voltage side switching element Q WH and low-voltage side switching element Q WL Insulated-gate bipolar transistors (IGBTs) are used, for example, in the switching elements. Freewheeling diodes are connected to the switching elements.

[0051] Three-phase AC current is output from the inverter 20 via the U-phase current path 50U, the V-phase current path 50V, and the W-phase current path 50W to drive the motor 21 (actuator). The motor 21 may be a linear motor, for example. The movable worktable 25 is driven by the motor 21.

[0052] Current measuring circuits 10U, 10V, and 10W are respectively inserted into the current path 50U for phase U, the current path 50V for phase V, and the current path 50W for phase W. As the current measuring circuits 10U, 10V, and 10W, the current measuring circuit 10 based on the first embodiment is used. Figure 1 The current path 50U for phase U, the current path 50V for phase V, and the current path 50W for phase W are respectively equivalent to the current path 50 inserted in the current measurement circuit 10 based on the first embodiment. Figure 1 The current measurement circuits 10U, 10V, and 10W measure the instantaneous values ​​of the AC current flowing through the current path 50U for phase U, the current path 50V for phase V, and the current path 50W for phase W at certain time intervals.

[0053] The current measurement values ​​output from the current measurement circuits 10U, 10V, and 10W are input to the driver 30. The driver 30 controls the switching element Q according to the instructions from the host controller 31 and the input current measurement values. UH Q UL Q VH Q VL Q WH Q WL Instructions from the host controller 31 may include, for example, target current values ​​for the U-phase, V-phase, and W-phase.

[0054] Next, refer to Figure 5 The control steps for motor 21 are explained. Figure 5 This is a flowchart showing the control steps of motor 21.

[0055] First, the current measurement circuits 10U, 10V, and 10W are respectively connected to a high-current sensor 11H. Figure 1 ) and 11L current sensor for small current applications Figure 1 ), Measure the current flowing through the U-phase current path 50U, the V-phase current path 50V and the W-phase current path 50W (step S1).

[0056] Select circuit 15 ( Figure 1 Based on the sensor outputs of the high-current sensor 11H and the low-current sensor 11L, one of the sensor outputs of the high-current sensor 11H and the low-current sensor 11L is selected and output as the current measurement value (step S2). The current measurement value is input to the driver 30.

[0057] For example, if the amplitude of the current is within the linear characteristic range R of the current sensor 11L for small current applications... LWithin one cycle, the sensor output of the small current sensor 11L is selected at all times. When the current amplitude exceeds the linear characteristic range R of the small current sensor 11L... L In this case, within one cycle, the selected current sensor switches between the low-current current sensor 11L and the high-current current sensor 11H.

[0058] The driver 30 controls the inverter 20 based on the sensor outputs (current measurement values) selected from the current measurement circuits 10U, 10V, and 10W respectively. By controlling the inverter 20, the operation of the motor 21 is controlled (step S3). Steps S1, S2, and S3 are repeated until the operation of the movable worktable 25 ends (step S4).

[0059] Next, the superior effects of the second embodiment will be explained.

[0060] In the second embodiment, the current measurement circuit 10 based on the first embodiment is used as the current measurement circuits 10U, 10V, and 10W. Figure 1 Therefore, even when switching between the low-current sensor 11L and the high-current sensor 11H, the current flowing through the current path 50U, 50V, and 50W will not be affected. Thus, the noise caused by switching can be eliminated, and the motor 21 can be controlled stably. For example, malfunctions of the movable worktable 25 caused by noise are less likely to occur.

[0061] When driving the movable stage 25, a large current must flow to enable its high-speed operation. Furthermore, to improve the positioning accuracy of the movable stage 25 when it stops, high accuracy is required for current measurement during low-current driving.

[0062] In order to measure the large current during high-speed operation, if only a high-current current sensor 11H is used, such as Figure 2 As shown, a large detection error Err is generated in the measurement value at a small current. H Due to this detection error, it is difficult to improve the positional accuracy of the movable stage 25 when it stops. In the second embodiment, a low-current sensor 11L is used for low-current measurement. Figure 1 Therefore, as Figure 2 As shown, the detection error Err L It becomes smaller. Therefore, it can improve the positioning accuracy when the movable worktable 25 stops.

[0063] Furthermore, such as Figure 3 As shown, since the quantization error is smaller at low current, positioning can be achieved with higher accuracy.

[0064] The above embodiments are examples, and it goes without saying that the structures shown in different embodiments can be partially replaced or combined. Similar effects produced by similar configurations in multiple embodiments are not mentioned sequentially in each embodiment. Furthermore, the present invention is not limited to the above embodiments. For example, it will be obvious to those skilled in the art that various changes, improvements, and combinations can be made.

Claims

1. A current measuring circuit, comprising: Multiple current sensors are inserted into a current path, the current flowing through the current path has a different relationship with the sensor output, and they are connected in series: The selection circuit selects one sensor output from multiple current sensors based on their respective sensor outputs and outputs the selected sensor output as the current measurement value.

2. The current measuring circuit according to claim 1, wherein, The plurality of current sensors each include a Hall element.

3. The current measuring circuit according to claim 2, wherein, The plurality of current sensors each include an analog-to-digital converter (AD converter) that converts the analog signal output from the Hall element into a digital signal, and the resolution of the AD converter differs among the plurality of current sensors.

4. The current measuring circuit according to any one of claims 1 to 3, wherein, Further equipped with an inverter, The alternating current output from the inverter flows through the current path.

5. A worktable device, comprising: The current measurement circuit according to claim 4; Movable worktable; An actuator, driven by the inverter, moves the movable worktable; and The driver controls the inverter based on the output from the current measurement circuit.

6. A control method that performs the following processing: Multiple current sensors are used to measure the current flowing through a current path. These current sensors are connected in series within the current path, and the relationship between the current flowing through the current path and the sensor outputs differs. Based on the respective sensor outputs of the plurality of current sensors, one sensor output is selected from the plurality of sensor outputs, and the actuator is controlled according to the selected sensor output.

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