Method for setting the operating point of a position measuring device and circuit arrangement

Abstract

Method for setting the operating point of a position measuring device (1) in which at least one sensor (5, 6, 7, 8) scans a dimensioned object (3), wherein an actual value (90) is determined by means of the sensor (5, 6, 7, 8), by means of which a manipulated variable (40) setting the operating point, namely a control voltage or a control current, of the position measuring device (1) is controlled, characterized in that the manipulated variable (40) is changed when the actual value (90) lies outside a dead range (T) defined by a lower limit (U) and an upper limit (O).

Description

[0001] The invention relates to a method for setting the operating point of a position measuring device, in which at least one sensor scans a physical dimension, and an actual value is determined by means of the sensor, by means of which a manipulated variable, namely a control voltage or a control current, of the position measuring device is controlled. A further aspect of the invention is a circuit arrangement with at least one sensor for scanning a physical dimension of a position measuring device, wherein an actual value can be determined by means of the sensor, by means of which a manipulated variable, namely a control voltage or a control current, of the position measuring device, which sets the operating point of the position measuring device, can be controlled. The invention further relates to a position measuring device with a physical dimension and such a circuit arrangement. Position measuring devices are used, among other things, in...Used to determine the position of moving components, for example, to detect longitudinal or angular position. The components can be equipped with a physical dimension that is scanned by one or more sensors, which can be arranged in an integrated circuit.

[0002] Such a position measuring device, which has a magnetic sensor designed as a Hall sensor, via which a magnetic measuring element is scanned, is known from DE 10 2010 050 026 A1.

[0003] DE 101 57 112 A1 discloses a control device for a position measuring device. Depending on a deviation signal, the luminous intensity of a light source varies; this light source serves as a guide for manually adjusting the scanning distance during the mounting of the scanning head.

[0004] A position measuring device based on the optical scanning of the measuring instrument is described in DE 103 39 366 A1. This position measuring device has several optical sensors that scan a measuring instrument having transparent and opaque areas.

[0005] In such position measuring devices, the operating point can shift over time due to aging effects. This shift manifests itself, for example, in the measurement signals detected by the sensors drifting in a certain direction. Therefore, in such position measuring devices, a control variable, such as a control voltage or a control current, is often regulated to set the operating point.

[0006] To control the manipulated variable, the position measuring device known from DE 103 39 366 A1 first determines an actual value using one or more optical sensors. Based on this actual value, a control voltage is continuously derived, which regulates the brightness of a light source to a variable setpoint and thus sets the operating point of the position measuring device.

[0007] Operating point shifts of position measuring devices can be compensated for using such control methods. However, a disadvantage of such methods is that a control behavior arises in the area around the setpoint, which can generate fluctuations in the measurement signals. In the position measuring device known from DE 103 39 366 A1, this can manifest itself, for example, in the alternating detection of stronger or weaker measurement signals. Such behavior is undesirable in position measuring devices, as it can distort the measurement result, especially if the fluctuations are already within the measurement accuracy range of the measuring device.

[0008] Therefore, the invention is based on the objective of enabling measurement with fewer measurement errors.

[0009] In a method of the type mentioned at the beginning, the problem is solved by changing the manipulated variable when the actual variable lies outside a dead zone defined by a lower bound and an upper bound.

[0010] Since changes to the manipulated variable are only made when the actual variable is outside the dead range, the manipulated variable remains unchanged in the procedure when the actual variable is within the dead range.

[0011] No measures are taken to adjust the operating point in the dead zone, so no fluctuations in the measurement signals occur, which can improve the measurement result of the position measuring device.

[0012] In principle, the measured actual value can depend on the position of the operating point of the position measuring device. Therefore, the manipulated variable that sets the operating point can influence the actual value. Thus, the position measuring device can have feedback in the form of a control loop, through which the manipulated variable can be controlled.

[0013] Preferably, a predetermined setpoint for adjusting the operating point lies within the deadband, so that changes to the manipulated variable in the area of ​​the desired operating point of the position measuring device can be prevented. Particularly preferably, the deviation of the upper and lower limits from the setpoint is less than 10% of the setpoint, and especially less than 6% of the setpoint.

[0014] It is particularly advantageous if the lower and / or upper cabinets are adjustable. Adjusting the lower and / or upper cabinets allows you to influence the position and size of the dead zone.

[0015] According to an advantageous embodiment of the method, the manipulated variable is increased when the actual value is lower than the lower limit and decreased when the actual value is higher than the upper limit. With this type of control behavior, the manipulated variable is only changed in the direction of the setpoint when there are significant deviations from it.

[0016] This method is particularly suitable for position measuring devices that incorporate an optical sensor, especially a photodiode sensor. It is advantageous if the brightness of a light source illuminating the measuring scale is adjusted via the control variable. Adjusting the brightness of the light source counteracts aging effects of the light source and / or the sensors.

[0017] Furthermore, the method can be applied to position measuring devices that incorporate a magnetic sensor. Preferably, the magnetic sensor is designed as a Hall sensor. In this context, it is advantageous if the manipulated variable is the control current of the Hall sensor, so that the drift of the Hall sensor can be compensated for by changing the manipulated variable.

[0018] Alternatively, other parameters influencing the operating point of the position measuring device can be set via the manipulated variable. Another possibility is that the gain of a sensor's measurement signal can be adjusted via the manipulated variable. In particular, adjusting the gain of the measurement signal can compensate for the drift of the amplifier and / or the drift of the sensor generating the measurement signal.

[0019] It is preferred that several sensors scan the measuring instrument. This allows the operating point to be set based on multiple measurement signals. The sensors can be arranged to generate periodic measurement signals, in particular sine and / or cosine signals. It is especially preferred that the sensors are arranged such that their measurement signals have a predetermined phase shift relative to each other, for example, 120° or 90°. This enables simple evaluation and, at the same time, highly accurate measurement.

[0020] The actual value used for control can be calculated as the sum of the measurement signals from multiple sensors, for example, to keep the DC component of sinusoidal signals constant. Alternatively, the sum of the squares of processed sensor measurement signals can be used, for example, to keep the amplitude of sinusoidal signals constant. By incorporating multiple sensors to determine the actual value, the control of the manipulated variable can be improved.

[0021] In a circuit arrangement of the type mentioned above, the task is solved by a controller designed such that the manipulated variable is changed when the actual value lies outside a deadband defined by a lower and an upper limit. This offers the same advantages as those already described in connection with the method for setting the operating point.

[0022] An advantageous embodiment provides that the lower and upper limits are selected such that a setpoint of the controller lies within the deadband, particularly in the middle of the deadband. Control-induced fluctuations of the manipulated variable and the measurement signals in the region of the desired operating point of the position measuring device can thus be eliminated, thereby improving the measurement accuracy.

[0023] Furthermore, it is advantageous if the circuit arrangement is designed as an integrated circuit, resulting in a compact design. The controller and the sensor(s) can be arranged in a separate integrated circuit or in a shared integrated circuit.

[0024] In a position measuring device of the type mentioned above, the problem is solved by providing a circuit arrangement of the type described above. This results in the same advantages that have already been described in connection with the method for setting the operating point.

[0025] The features and designs explained in the method can also be used alone or in combination in the circuit arrangement and the position measuring device.

[0026] Further details and advantages of the invention will be explained below with reference to the exemplary embodiment shown in the drawings. This shows: Fig. 1 a block diagram of a position measuring device and Fig. 2 a diagram with several time-dependent signal profiles of the position measuring device according to Fig. 1 to illustrate the processes involved in setting the operating point.

[0027] The Fig. Figure 1 shows a block diagram of an optical position measuring device 1, which can be used as a position encoder to determine the absolute position of a movable component. The position measuring device 1 can, for example, be designed as an optical rotary encoder, which can be used to determine the absolute angular position of a rotatably mounted component.

[0028] The position measuring device 1 has a measuring element 3 which is connected to the movable component. In the case of a component rotatably mounted on a shaft, the measuring element 3 can be designed in the form of a disk which sits on the same shaft as the component and is rotatable together with it.

[0029] The scale 3 is movably arranged between a light source 4, designed as an LED, and four sensors 5, 6, 7, 8 of the position measuring device 1, which scan the scale 3. The scale 3 is illuminated by the light source 4. The scale 3 is made of a translucent material and has an opaque measuring scale, so that the light emitted by the LED 4 can only fall on the sensors 5, 6, 7, 8 in predetermined positions of the scale. By moving the measuring instrument 3 relative to the LED 4 and the sensors 5, 6, 7, 8, the brightness measurable by the sensors 5, 6, 7, 8 is modulated, so that by evaluating the measurement signals 50, 60, 70, 80 of the sensors 5, 6, 7, 8, the absolute position of the measuring instrument 3 and thus the absolute position of the component connected to the measuring instrument 3 can be determined.Position determination can be carried out using evaluation electronics not shown in the figures.

[0030] The optical sensors 5, 6, 7, 8 can be configured as photodiodes or phototransistors. The sensors 5, 6, 7, 8 can be arranged in an integrated circuit assembly 9 on a common substrate. To block stray light, an aperture 2 is provided between the sensors 5, 6, 7, 8 and the scale 3 scanned by the sensors. In applications where stray light is negligible, the aperture 2 can be omitted.

[0031] The time course of the measurement signals 50, 60, 70, 80 of sensors 5, 6, 7, 8 is shown in Fig. Figure 2 shows the sensors 5, 6, 7, and 8 arranged in the integrated circuit assembly 9 such that, when scanning the moving measuring element 2, they generate periodic measurement signals 50, 60, 70, and 80, which have a predetermined phase shift relative to each other. The measurement signals 50, 60, 70, and 80 are periodic signals, in particular voltages of the type of sine or cosine signals. In this embodiment, the phase shift between the four measurement signals 50, 60, 70, and 80 is 90° (π / 2).

[0032] The operating point of the optical position measuring device 1 is determined by the brightness of LED 4. The amplitude of the measurement signals 50, 60, 70, 80 depends on the absolute brightness of LED 4. Over time, variations in the brightness of LED 4 can occur, for example, due to aging changes in the LED 4 or changes in ambient temperature. These fluctuations in brightness caused by LED 4 have a low frequency compared to the brightness changes generated by the movement of the measuring scale 3 and detected by sensors 5, 6, 7, 8. This long-term drift in brightness can impair the measurement accuracy of the position measuring device if the actual brightness achieved deviates significantly from the specified target value of the desired operating point of the position measuring device 1.

[0033] Therefore, the operating point of the position measuring device 1 is set via a control system. For this purpose, the measurement signals 50, 60, 70, 80 from sensors 5, 6, 7, 8 are amplified by amplifiers 500, 600, 700, 800 and fed to adders 901, 902, 903 arranged in an addinger tree configuration. The amplitudes of the amplified measurement signals 50, 60, 70, 80 are added by the adders. The sum of the amplified measurement signals 50, 60, 70, 80 forms the actual value 90 for setting the operating point. The amplifiers 500, 600, 700, 800 and the adders 901, 902, 903 are arranged in an integrated circuit arrangement 9 on a common substrate. Optionally, sensors 5, 6, 7, 8 can also be arranged in the integrated circuit arrangement 9.

[0034] In the position measuring device 1, the brightness of LED 4 is controlled to set the operating point. The brightness of LED 4 can be controlled via its power consumption. The control variable 40 for setting the operating point therefore represents the operating voltage or the operating current of LED 4.

[0035] The change in brightness of LED 4 is detected by sensors 5, 6, 7, and 8. Thus, the manipulated variable 40 not only influences the position of the operating point of the position measuring device 1, but also the actual value 90, resulting in feedback.

[0036] Conventional control methods for setting the operating point can cause fluctuations in the brightness of LED 4. These fluctuations in LED brightness can lead to fluctuations in the measurement signals 50, 60, 70, 80 of sensors 5, 6, 7, 8, which are within the measurement accuracy range of the position measuring device 1. Since the frequency of these control-induced fluctuations is typically in the range of the frequency of the brightness fluctuations at sensors 5, 6, 7, 8 generated by the movement of the scale 3, the measurement result can be degraded.

[0037] To improve the measurement result, the following is therefore carried out on the position measuring device 1 according to Fig. 1. The manipulated variable 40 is then changed if the actual variable 90 lies outside a dead zone T defined by a lower bound U and an upper bound O, cf. Fig.2. Changes to the manipulated variable 40 are only made if the actual variable 90 lies outside the dead zone T. The manipulated variable 40 remains unchanged in this procedure if the actual variable 90 lies within the dead zone T. No adjustments to the operating point are made within the dead zone T, thus preventing fluctuations in the measurement signals 50, 60, 70, and 80, which improves the measurement result of the position measuring device 1.

[0038] To control the manipulated variable 40, a comparator 100, a controller 200 and an integrator 300 are provided in the integrated circuit arrangement 9 of the position measuring device 1, the function of which will be described below.

[0039] The comparator 100, configured as a subtractor, calculates the control deviation 20 from the actual value 90 and a predefined setpoint 10. The control deviation 20 is fed to a controller 200, which is configured to change the manipulated variable 40 when the actual value 90 lies outside the deadband T. The output 30 of the controller 200 is fed to an integrator 300, which calculates the manipulated variable 40.

[0040] Controller 200 increases the manipulated variable 40 when the actual variable 90 is less than the lower limit U. Conversely, if the actual variable 90 is greater than the upper limit O, the manipulated variable 40 is decreased. Thus, the control system only intervenes when the upper limit O is exceeded or the lower limit U is undershot. Within the deadband T, the actual variable 90 can change without controller 20 altering the manipulated variable 40. Therefore, control only occurs when the control deviation 20 is relatively large.

[0041] The upper limit O lies above the setpoint, and the lower limit U lies below the setpoint. Preferably, the size of the dead zone T around the setpoint 10 is chosen such that the upper limit O is less than 1.1 times the setpoint and the lower limit U is more than 0.9 times the setpoint. Particularly preferably, the upper limit O is less than 1.06 times the setpoint and the lower limit U is more than 0.94 times the setpoint.

[0042] The lower barrier U and the upper barrier O of the position measuring device 1 are adjustable, so that the position and size of the dead zone T can be set. Thus, the position and size of the dead zone T can be adapted to the requirements of the respective application.

[0043] In a variation of the embodiment, the gain of the amplifiers 500, 600, 700, 800 can be set via the control variable 40 instead of the brightness of the LED 4.

[0044] In a further modification of the exemplary embodiment, a position measuring device 1 can be provided, which is designed as a magnetic position measuring device. The magnetic position measuring device can have a magnetic scale and magnetic sensors for scanning the magnetic scale, which are designed as Hall sensors. With such a magnetic position measuring device, the control current of the Hall sensor can be regulated as described above to set the operating point.

[0045] In the position measuring devices 1 described above, a method is used to set the operating point in which a sensor 5, 6, 7, 8 determines an actual value 90, which is then used to control a manipulated variable 40 that sets the operating point. The manipulated variable 40 is changed when the actual value 90 lies outside a dead zone T defined by a lower limit U and an upper limit O. This reduces control-induced fluctuations of the measurement signals 50, 60, 70, 80 in the operating point region and thus improves the measurement result. Reference symbol: 1 Position measuring device 2 aperture 3. Physical embodiment 4 light sources 5 Sensor 6 Sensor 7 Sensor 8 Sensor 9 integrated circuit arrangement 10 Target value 20 rule deviations 30 Initial size 40 Control variable 50 Measurement signal 60 Measurement signal 70 Measurement signal 80 Measurement signal 90 Actual size 100 comparison tools 200 controllers 300 Integrator 500 amplifiers 600 amplifiers 700 amplifiers 800 amplifiers 901 Adder 902 Adders 903 Adders O upper cabinet T Dead area U-shaped base cabinet

Claims

[1] Method for setting the operating point of a position measuring device (1) in which at least one sensor (5, 6, 7, 8) scans a dimensioned object (3), wherein an actual value (90) is determined by means of the sensor (5, 6, 7, 8), by means of which a control variable (40) setting the operating point, namely a control voltage or a control current, of the position measuring device (1) is controlled, characterized by , that the manipulated variable (40) is changed when the actual variable (90) lies outside a dead zone (T) defined by a lower bound (U) and an upper bound (O). [2] Method according to claim 1, characterized by , that the lower cabinets (U) and / or the upper cabinets (O) are adjustable. [3] Method according to any one of the preceding claims, characterized by , that the sensor (5, 6, 7, 8) is an optical sensor, in particular a sensor of the type of a photodiode, or a magnetic sensor, in particular a Hall sensor. [4] Method according to any one of the preceding claims, characterized by , that the brightness of a light source (4) illuminating the physical medium (3) is adjusted via the control variable (40). [5] Method according to any one of claims 1 to 3, characterized by , that the manipulated variable (40) is a control current of a Hall sensor. [6] Method according to any one of the preceding claims, characterized by , that the gain of a measurement signal (50, 60, 70, 80) of the sensor (5, 6, 7, 8) is set via the control variable (40). [7] Method according to any one of the preceding claims, characterized by , that the actual value (90) is determined by means of several sensors (5, 6, 7, 8), in particular as the sum of the measurement signals (50, 60, 70, 80) of several sensors (5, 6, 7, 8). [8] Circuit arrangement with at least one sensor (5, 6, 7, 8) for scanning a dimension (3) of a position measuring device (1), wherein an actual value (90) can be determined by means of the sensor (5, 6, 7, 8), via which a control variable (40), namely a control voltage or a control current, of the position measuring device (1) can be controlled, characterized by a controller (200) which is designed such that the manipulated variable (40) is changed when the actual variable (90) lies outside a dead range (T) defined by a lower limit (U) and an upper limit (O). [9] Circuit arrangement according to claim 8, characterized by , that the circuit arrangement (9) is designed as an integrated circuit arrangement (9). [10] Position measuring device with a measuring element (3) and a circuit arrangement (9) according to one of claims 8 or 9.

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