Current measurement circuit, stage device, and actuator control method

Abstract

The present invention provides a current measurement circuit that can suppress the generation of noise in the current path of the object being measured. [Solution] The relationship between the current flowing through the current path and the sensor output differs, and multiple current sensors connected in series are inserted into the current path. A selection circuit selects one sensor output from the multiple sensor outputs based on the sensor output from each of the multiple current sensors, and outputs the selected sensor output as the current measurement value.

Description

Technical Field

[0001] The present invention relates to a current measurement circuit, a stage device, and a method for controlling an actuator.

Background Art

[0002] A circuit that switches two current detection units according to the magnitude of the current flowing through a current path to be measured and detects the current is known (Patent Document 1). The current detection unit for detecting a small current detects the current flowing through a current detection transistor connected in parallel to a transistor that allows current to flow through the current path. The current detection unit for detecting a large current is connected in series to the transistor that allows current to flow through the current path and directly detects the current flowing through the current path. When detecting a small current, the loss caused by the current detection unit is reduced by conducting a switch connected in parallel to the current detection unit for large current.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the circuit described in Patent Document 1, since the switch is turned on and off during measurement of a large current and measurement of a small current, noise generated during switching is superimposed on the current. An object of the present invention is to provide a current measurement circuit capable of suppressing the generation of noise in a current path to be measured. Another object of the present invention is to provide a control method for controlling an actuator using this current measurement circuit.

Means for Solving the Problems

[0005] According to one aspect of the present invention, Inserted into the current path, a plurality of current sensors having different relationships between the current flowing through the current path and the sensor output, and connected in series with each other, Based on the sensor outputs from each of the plurality of current sensors, a selection circuit that selects one sensor output from the plurality of sensor outputs and outputs the selected sensor output as a current measurement value A current measurement circuit including is provided.

[0006] According to another aspect of the present invention, The current measurement circuit, A movable stage, An actuator driven by the inverter to move the movable stage, A driver that controls the inverter based on the output from the current measurement circuit A stage device including is provided.

[0007] According to still another aspect of the present invention, Measuring the current flowing through the current path with a plurality of current sensors inserted in series in the current path and having different relationships between the current flowing through the current path and the sensor output, Based on the sensor outputs of each of the plurality of current sensors, a control method is provided that selects one sensor output from the plurality of sensor outputs and controls an actuator based on the selected sensor output.

Advantages of the Invention

[0008] Since the plurality of current sensors are connected in series with each other and inserted into the current path, the current flowing through the current path always flows through the plurality of current sensors, and sensor outputs can always be obtained from the plurality of current sensors. Since the selection circuit selects one from the plurality of sensor outputs, there is no influence on the current path at the time of selection. Therefore, generation of noise in the current path to be measured can be suppressed.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a block diagram of a current measurement circuit 10 according to a first embodiment. [Figure 2] Figure 2 is a graph showing an example of 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, as well as the relationship between the current sensor selected by the selection circuit 15 and the current Io. [Figure 3] Figure 3 is a graph showing an example of the relationship between the current Io and the digitally converted output voltage Vo. [Figure 4] Figure 4 is a block diagram of the stage apparatus according to the second embodiment. [Figure 5] Figure 5 is a flowchart showing the control procedure for motor 21. [Modes for carrying out the invention]

[0010] The current measurement circuit according to the first embodiment will be described with reference to Figures 1 to 3. Figure 1 is a block diagram of a current measurement circuit 10 according to 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 with each other and inserted into the current path 50 through which the current to be measured flows. The relationship between the current flowing through the current path 50 and the sensor output differs between the two current sensors 11H and 11L, as will be explained with reference to Figure 2. One current sensor 11H is a sensor for high currents, and the other current sensor 11L is a sensor for low currents.

[0011] The current sensor 11H for high currents includes a current detection element 12H and an AD converter 13H, while the current sensor 11L for low currents includes a current detection element 12L and an AD converter 13L. Each of the current detection elements 12H and 12L outputs a voltage corresponding to the current flowing through the current path 50. For example, Hall elements can be used as the current detection elements 12H and 12L.

[0012] AD converters 13H and 13L convert the voltages (analog signals) output from current detection elements 12H and 12L, respectively, into digital signals. The digitally converted signals are referred to as "sensor outputs." The resolution and full-scale voltage values are different between the two AD converters 13H and 13L.

[0013] Based on the sensor outputs from current sensors 11H and 11L respectively, selection circuit 15 selects one sensor output from the two sensor outputs and outputs the selected sensor output as the current measurement value. Selection circuit 15 is composed of, for example, an FPGA (field-programmable gate array). When selection circuit 15 is composed of an FPGA, faster processing is possible compared to the case of being composed of a CPU and software.

[0014] Next, referring to FIG. 2, the input / output characteristics of the two current detection elements 12H and 12L (FIG. 1) will be described. FIG. 2 is a graph showing an example of the relationship between the current Io flowing through the current path 50 (FIG. 1) and the output voltage Vo of the current detection elements 12H and 12L, and the relationship between the current sensor selected by the selection circuit 15 (FIG. 1) 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 detection elements 12H and 12L, and the vertical axis of the lower graph represents the other of the current sensors 11H and 11L.

[0015] The thin solid line in the upper graph indicates the input / output characteristic C H of the current detection element 12H for large currents, and the thick solid line indicates the input / output characteristic C L of the current detection element 12L for small currents. The input / output characteristics C H , C L are point-symmetric about the origin O. The linear characteristic range R H of the current detection element 12H for large currents is wider than the linear characteristic range R L of the current detection element 12L for small currents. The maximum values of the linear characteristic ranges R H , R L are denoted as I H , I L respectively.

[0016] 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 detection elements 12H and 12L. That is, the same current flows through the low-current current detection element 12L as the current flowing through the high-current current detection element 12H. Therefore, the low-current current detection element 12L has the same linear characteristic range R as the high-current current detection element 12H. H The maximum value of the current I H A device with the above current rating values ​​is used. However, the current Io is within the linear characteristic range R. L The maximum value of the current I L When this value is exceeded, the output of the low-current current sensing element 12L saturates.

[0017] Detection error Err of high-current current sensing element 12H H The detection error Err of the current sensing element 12L for small currents L Larger than. In Figure 2, the detection error Err H Err L An example of the range is shown by the dashed line. Note that in Figure 2, the detection error Err H Err L The range is shown as being larger than it actually is.

[0018] The selection circuit 15 tentatively determines the current value Io based on the sensor output of the high-current current sensor 11H. The tentatively determined current value is within the linear characteristic range R. L When the current Io increases, the selection circuit 15 selects the sensor output of the low-current current sensor 11L. L The maximum value I L When the current exceeds a certain threshold, the selection circuit 15 switches the selected current sensor from the low-current current sensor 11L to the high-current current sensor 11H. When the current Io decreases and the provisionally determined current value falls below the switching threshold I1, 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 within the linear characteristic range R L The maximum value I LIt is set to a smaller value. In this way, a hysteresis characteristic is introduced to the timing of the current switching.

[0019] When the current Io is small, the low-current current sensor 11L is selected, resulting in a smaller detection error compared to when the high-current current sensor 11H is used for current measurement. Furthermore, the linear characteristic range R of the low-current current sensor 11L is also reduced. L When the current exceeds a certain value, the high-current sensor 11H is selected, allowing the current Io to be measured while maintaining linearity.

[0020] Next, the relationship between the output voltage Vo, which has been converted to a digital signal, and the current Io will be explained with reference to Figure 3. Figure 3 is a graph showing an example of the relationship between the current Io and the digitally converted output voltage Vo. When the AD converters 13H and 13L convert the voltage (analog signal) output from the current sensing elements 12H and 12L to a digital signal, quantization errors occur. Due to these quantization errors, the output voltage Vo changes in a stepwise manner with respect to the current Io. Note that in Figure 3, the quantization error is shown as an exaggeration compared to the actual quantization error.

[0021] The full scale of the AD converter 13L of the low-current current sensor 11L is within the linear characteristic range R L The maximum value of the current I L The output voltage V when a current equivalent to this flows. L It is set based on the following: The full scale of the AD converter 13H of the current sensor 11H for high current is the linear characteristic range R H The maximum value of the current I H The output voltage V when a current equivalent to this flows. H It is set based on the current sensor 11L for small currents and the AD converter 13L, where the voltage is the output voltage V L Within the following range, a current sensor 11H with a resolution higher than that of the AD converter 13H is used. Therefore, the quantization error is smaller compared to when measuring the current using only the current sensor 11H.

[0022] Next, we will describe the excellent effects of the first embodiment. In the first embodiment, a current sensor 11H for high currents and a current sensor 11L for low currents are used to widen the current measurement range and reduce detection errors in the low current region (detection error Err in Figure 2). L Err H This allows for a reduction in the quantization error (corresponding to the quantization error shown in Figure 3). Furthermore, it allows for a reduction in the quantization error in the low-current region.

[0023] Since the two current sensors 11H and 11L, which are inserted in series in the current path 50, are connected in series with each other, the current Io is constantly measured by the two current sensors 11H and 11L. The current Io is within the linear characteristic range R for small currents. L The maximum value of the current I L Furthermore, when the selected sensor output switches between the two current sensors 11H and 11L when the switching threshold I1 changes, the current path 50 (Figure 1) does not affect the switching in any way. Therefore, it is possible to prevent the generation of noise during switching.

[0024] In the first embodiment, Hall elements are used for the current sensing elements 12L and 12H. In the Hall element, the voltage generated by the Hall effect is detected and output by an isolation amplifier, so the current path to be measured (primary circuit) and the output terminal (secondary circuit) that outputs the measurement result are isolated. Therefore, a high level of safety can be ensured. Furthermore, when a large current flows through the current path to be measured, the Hall element for small currents will be used in the nonlinear region, but it is possible to select an element with specifications that will remain within the rated range even for currents in the nonlinear region. Moreover, in the Hall element for current detection, a constant magnetic field is applied to the current path made of semiconductor, and the magnetic field does not change with the magnitude of the current. Therefore, magnetic saturation caused by the properties of magnetic materials does not occur.

[0025] Next, a modified example of the first embodiment will be described. In the first embodiment, two current sensors 11H and 11L connected in series are inserted into the current path 50 (Figure 1), but three or more current sensors connected in series may be inserted. Also, in the first embodiment, Hall elements are used as current detection elements 12H and 12L, but other current detection elements that output a voltage corresponding to the amount of current may be used.

[0026] For example, as a current sensing element 12L for small currents, the maximum current (current I in Figure 2) is used. H A current transformer designed to prevent magnetic saturation during high current may be used, and a shunt resistor may be used as the current sensing element 12H for high currents. The current sensing element 12L for low currents may be used for the maximum current (current I in Figure 2). H By designing it so that magnetic saturation does not occur when the current is large (current I in Figure 2), the current can be reduced. L (larger current) to small current (current I in Figure 2) L Even when the current transitions rapidly to a smaller current, the current transitions within a range where magnetic saturation does not occur. Therefore, compared to the case where the current sensing element 12L transitions from a state where magnetic saturation occurs (low inductance state) to a state where magnetic saturation does not occur, the decrease in the accuracy of reading the current value is suppressed. Alternatively, two current transformers with different numbers of turns in the secondary winding may be used as the current sensing elements 12L and 12H for small and large currents, respectively.

[0027] In the first embodiment, as shown in Figure 2, the linear characteristic range R of the current detection element 12L for small currents L In this configuration, the relationship between the current Io and the output voltage Vo is the same for both the high-current current sensing element 12H and the low-current current sensing element 12L. Other configurations include the linear characteristic range R of the low-current current sensing element 12L. L In this configuration, the relationship between the current Io and the output voltage Vo may differ between the high-current current detection element 12H and the low-current current detection element 12L. For example, for the same current Io, elements may be used such that the output voltage Vo of the low-current current detection element 12L is higher than the output voltage Vo of the high-current current detection element 12H.

[0028] 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 necessary to prevent magnetic saturation even at high currents. In order to prevent magnetic saturation at high currents, the dimensions of the magnetic material must be increased, which means that the elements become large depending on the rated maximum current. In contrast, when using Hall elements, there is the advantage that magnetic saturation does not occur, as has already been explained.

[0029] Furthermore, when shunt resistors are used for the current sensing elements 12L and 12H, the primary and secondary circuits are not isolated from each other, so it is preferable to insert an isolation IC in the subsequent stage to ensure sufficient safety. In addition, since a large current flows through the shunt resistor for small currents, abnormal heat generation may occur, and the shunt resistor for small currents may be damaged. When Hall elements are used, as already explained, the primary and secondary circuits are isolated from each other, so sufficient safety is ensured. Furthermore, as already explained, it is possible to use Hall elements for small currents that are not damaged even when a large current flows through them.

[0030] As mentioned above, from the standpoint of preventing magnetic saturation and element damage, it is preferable to use Hall elements as current sensing elements 12L and 12H rather than using current transformers or shunt resistors.

[0031] Next, a stage apparatus and control method according to the second embodiment will be described with reference to Figures 4 and 5.

[0032] Figure 4 is a block diagram of a stage device according to 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 power line and the low-voltage power line of the inverter 20. The inverter 20 has a high-voltage switching element Q for the U phase. UH and the low-voltage switching element Q UL , V-phase high-voltage side switching element Q VH and the low-voltage switching element Q VL , high-voltage side switching element Q for W phase WHand the low-voltage switching element Q WL It includes the following. Each of the switching elements is, for example, an insulated-gate bipolar transistor. Each of the switching elements is connected to a freewheeling diode.

[0033] Three-phase alternating current is output from the U-phase current path 50U, the V-phase current path 50V, and the W-phase current path 50W of the inverter 20, and the motor 21 (actuator) is driven. For example, a linear motor is used as the motor 21. The movable stage 25 is driven by the motor 21.

[0034] Current measurement circuits 10U, 10V, and 10W are inserted into the U-phase current path 50U, the V-phase current path 50V, and the W-phase current path 50W, respectively. The current measurement circuit 10 (Figure 1) according to the first embodiment is used as the current measurement circuits 10U, 10V, and 10W. Each of the U-phase current path 50U, the V-phase current path 50V, and the W-phase current path 50W corresponds to the current path 50 (Figure 1) into which the current measurement circuit 10 according to the first embodiment is inserted. The current measurement circuits 10U, 10V, and 10W measure the instantaneous value of the AC current flowing through the U-phase current path 50U, the V-phase current path 50V, and the W-phase current path 50W, respectively, with a fixed time step size.

[0035] The current measurement values ​​output from the current measurement circuits 10U, 10V, and 10W are input to the driver 30. Based on the commands from the higher-level controller 31 and the input current measurement values, the driver 30 controls the switching element Q UH Q UL Q VH Q VL Q WH Q WL This controls the currents. Commands from the higher-level controller 31 include, for example, current target values ​​for the U-phase, V-phase, and W-phase.

[0036] Next, the control procedure for motor 21 will be explained with reference to Figure 5. Figure 5 is a flowchart showing the control procedure for motor 21.

[0037] First, the current measurement circuits 10U, 10V, and 10W each measure the current flowing through the U-phase current path 50U, the V-phase current path 50V, and the W-phase current path 50W using the high-current current sensor 11H (Figure 1) and the low-current current sensor 11L (Figure 1) respectively (Step S1).

[0038] The selection circuit 15 (Figure 1) selects one of the sensor outputs of the high-current sensor 11H and the low-current sensor 11L based on the sensor outputs of the high-current sensor 11H and the low-current sensor 11L, and outputs it as a current measurement value (step S2). The current measurement value is input to the driver 30.

[0039] For example, the linear characteristic range R of the current sensor 11L for small currents, where the current amplitude is small. L Within this range, the sensor output of the low-current current sensor 11L is selected at all time points within one cycle. The amplitude of the current is within the linear characteristic range R of the low-current current sensor 11L. L If the current exceeds a certain value, the selected current sensor switches between the low-current current sensor 11L and the high-current current sensor 11H within one cycle.

[0040] The driver 30 controls the inverter 20 based on the sensor output (current measurement value) selected by the current measurement circuit 10U, 10V, and 10W, respectively. The operation of the motor 21 is controlled by the control of the inverter 20 (step S3). Steps S1, S2, and S3 are repeated until the operation of the movable stage 25 is completed (step S4).

[0041] Next, we will describe the excellent effects of the second embodiment. In the second embodiment, the current measurement circuit 10 (Figure 1) from the first embodiment is used as the current measurement circuit 10U, 10V, and 10W. Therefore, even if switching occurs between the low-current current sensor 11L and the high-current current sensor 11H, the current flowing through the current paths 50U, 50V, and 50W is not affected. As a result, the effects of noise caused by switching are eliminated, and the motor 21 can be controlled stably. For example, malfunctions of the movable stage 25 caused by noise become less likely.

[0042] When driving the movable stage 25, a large current is required to operate it at high speed. Furthermore, in order to improve the positioning accuracy when the movable stage 25 is stopped, high precision is required for current measurement when driving with a small current.

[0043] When using only the high-current current sensor 11H to measure high currents during high-speed operation, a large detection error Err occurs in the measurement value at low currents, as shown in Figure 2. H This results in a detection error. Due to this detection error, it is difficult to improve the positional accuracy of the movable stage 25 when it is stopped. In the second embodiment, when measuring small currents, a current sensor 11L for small currents (Figure 1) is used, so as shown in Figure 2, the detection error Err L This reduces the size of the movable stage 25 when it is stopped. As a result, the positioning accuracy of the movable stage 25 when it is stopped can be improved.

[0044] Furthermore, as shown in Figure 3, the quantization error at low currents is reduced, making it possible to position the sensor with higher precision.

[0045] The embodiments described above are illustrative, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments is possible. Similar effects and benefits from similar configurations in multiple embodiments will not be mentioned sequentially for each embodiment. Furthermore, the present invention is not limited to the embodiments described above. For example, it will be obvious to those skilled in the art that various modifications, improvements, and combinations are possible. [Explanation of symbols]

[0046] 10, 10U, 10V, 10W current measurement circuit 11H High-current current sensor 11L Low-current current sensor 12H, 12L current sensing element 13H, 13L AD converter 15 Selection Circuit 20 Inverters 21 Motor 22 AC power supply 23 Rectifier circuit 24 smoothing capacitors 25 movable stages 30 drivers 31 Top Controller 50, 50U, 50V, 50W current path

Claims

1. Multiple current sensors are inserted into a current path, and the relationship between the current flowing through the current path and the sensor output is different, and these sensors are connected in series with each other. A selection circuit that, based on the sensor output from each of the plurality of current sensors, selects one sensor output from the plurality of sensor outputs and outputs the selected sensor output as a current measurement value. A current measurement circuit is provided.

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

3. The current measurement circuit according to claim 2, wherein each of the plurality of current sensors includes an AD converter that converts an 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. Furthermore, it is equipped with an inverter, The current measuring circuit according to any one of claims 1 to 3, wherein the alternating current output from the inverter flows through the current path.

5. The current measuring circuit according to claim 4, A movable stage and An actuator driven by the inverter moves the movable stage, Based on the output from the current measurement circuit, a driver controls the inverter. A stage device equipped with the following features.

6. Multiple current sensors are inserted in series with the current path, and the relationship between the current flowing through the current path and the sensor output is different for each sensor, and the current flowing through the current path is measured. A control method that selects one sensor output from the plurality of current sensors based on the sensor output of each of the plurality of current sensors, and controls an actuator based on the selected sensor output.

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