CN116336923A - Displacement sensor for measuring length by utilizing multiple Hall sensor chips - Google Patents

Abstract

As shown in figure 1 of the specification, the invention consists of two parts, namely a magnet A1 arranged on a moving object, a circuit board A2 provided with a plurality of Hall sensing devices and fixed below the magnet, wherein a plurality of Hall sensing devices are arranged on the circuit board at equal intervals.

Description

Displacement sensor for measuring length by utilizing multiple Hall sensor chips

Technical field:

the invention relates to a device for contactlessly measuring the displacement of a target object.

The background technology is as follows:

the hall effect is an effect of the interaction of a current in a conductive material with a magnetic field to create an electromotive force, the further the magnet is from the hall effect sensor chip in space, the smaller the voltage the magnet induces at the hall effect sensor chip. Based on this, we can derive the distance of the magnet from the sensor chip by this principle. When the magnet is arranged at the top of the chip and is shifted leftwards and rightwards, the induced voltage also changes correspondingly, when the magnet is arranged at the positive top, the induced voltage is the largest, and when the magnet is shifted, the voltage is reduced. Of course, this change is related to the distance between the magnet and the chip, which is not linear, but the farther the bias is to the left and right, the smaller the induced voltage is, which is a rule that is determined. The present invention utilizes this principle to measure the length of the position shift between objects, and because the sensor chips are uniformly arranged on the whole measuring scale, it is possible to determine the position of the magnet on the scale.

The invention comprises the following steps:

see fig. 1. The measuring device consists of a measuring ruler and a magnet arranged in a measuring moving object.

The measuring ruler is a strip-shaped circuit board, N Hall sensor chips are equidistantly arranged in the circuit board, for example, every 10mm, one sensor chip is placed, and if the ruler with the length of 1 meter is actually required to be measured, 102 sensor chips (the sensors at two ends are not used for direct measurement) are needed to be placed. (the total rule occupies 1010mm in length and 1000mm in measurement range)

Working principle:

1. when the power-on is performed, the output voltages of all the sensors are checked one by one, and the current detection target (namely, the magnet) can be confirmed to be closest to the sensor according to the highest output voltage of the sensor chip. We can derive the approximate location of the current sensor (e.g. the 25 th sensor voltage is highest, then if the chip distance is 1mm, then the current approximate location should be between 24mm and 25 mm). The 3 sensors on the left and right are used as tracking detection sensors. For example, in fig. 1, the magnet is located above the C2 sensor, and then the 3 sensors of C1, C2, and C3 are selected as the sensor chips that need to track and measure.

2. The 3 sensor chips closest to the magnet in all the sensor chips in the device are taken as measuring objects, wherein the sensor C2 is called a central sensor and is mainly used for measuring, and the sensor chips C1 and C3 on two sides can be used for judging whether the current measuring object (magnet) is far left or far right (when being far left or far right and equidistant from the central sensor), for example, if the voltages at C2 are measured only when they are 1mm apart, the voltages at C2 are equal at both positions, so that the right and left side determination is performed by the voltages at C1 and C3, and the tracking of the sensor is switched (i.e., the 3 sensor chips to be tracked are switched to the right or left) when the magnet continues to move to the right or left. By measuring the induced voltage on the center sensor, we can know the current accurate position, and obviously, the magnet is at its maximum induced voltage when it is just on top of the center sensor C2. The farther the center is, the smaller the induced voltage is, of course, the voltage is not in a proportional linear relationship with the moving position, therefore, we need to perform a compensation algorithm to obtain the accurate position, according to experiments, when using an AD with 16-bit resolution, the proper design can make our resolution to be within 1um, so that the position of the magnet is accurately known. The voltage value in the range of a sensor is stored in FLASH in the MCU at intervals of a certain distance, for example, at intervals of 50um, and when the measured voltage is a certain value, the accurate value of the current position can be obtained by a linear interpolation method. For example, when this voltage is measured to be the maximum value, it can be known that the current position is at the very top of the chip. When this voltage is at a minimum, the current position will be at the midpoint of the two chips, such as at the midpoint of C1 and C2, with the voltage induced on C2 being at a minimum, and moving to the left will switch to the C1-centered sensor chip. And at other voltages, the current position value is calculated by a table look-up and interpolation method. Accordingly, the error will theoretically be below 50um, and in practice the error will of course be smaller than this.

3. When the magnet moves, when the magnet moves to the left or right, the induced voltage on the chips at two sides is larger than the induced voltage of the originally set central sensor chip, for example, when the magnet moves to the left and passes through the midpoint between C1 and C2, the induced voltage of the C1 sensor chip is larger than the induced voltage of the C2 sensor chip, at this time, the C1 sensor chip is taken as the central sensor chip, and the current position can be obtained by measuring the voltage on the C1 sensor chip. At this point we successfully performed the switching of the central sensor chip. Software uses C1 sensor chip as the center sensor chip and C0 as the left sensor chip and C2 as the right sensor chip. We then have 3 sensor chips C0, C1, C2 as the sensor chips for the tracking measurement. By analogy, we have also obtained accurate magnet positions. Of course, the sensor chips at the leftmost and rightmost ends are not used for detection but are used for judgment only, and thus the measurement range is (number of sensors-2) the sensor interval. For example, a1 meter rule, 10mm sensor chip spacing, the number of sensor chips is 102.

Since the speed of AD conversion is on the order of microseconds, the response speed (output speed) of this sensor chip is quite high. On the order of tens of microseconds (i.e., the period of time for updating the output position) can be reached. Therefore, the sensor is a position measuring device with high response speed in principle.

4. When the magnet moves above the leftmost or rightmost sensor chip, we act as a special treatment where the displacement values are set to 0 and maximum, respectively. That is, when the sensor chip at the two ends is moved to the leftmost or rightmost side, the sensor chip at the two ends is not used for measurement, for example, for the above-mentioned 1 meter long rule, the interval is 10mm, and the 1 st sensor chip and the 102 th sensor chip are not used for accurate measurement because the measured value is fixed to 0 or 1000mm when the induced voltage moved to the two sensor chips is maximum.

5. When the magnet exceeds the detection area, a large voltage cannot be detected on the three sensor chips that are being tracked (in which case the voltage of all 3 sensor chips is low because the magnet is lost), which is the missing magnet. At this time, the circuit continuously detects the voltages of all hall sensor chips (in the above example, 102 sensor chips all the voltages are measured) until the magnet is captured again when a voltage higher than a certain set threshold value is reached. A fault light may be caused to flash to indicate that the magnet is currently lost and automatically enter an operational state immediately upon capture of the magnet.

Description of the drawings:

FIG. 1 is a schematic view of the installation of a Hall sensor and a moving object (magnet)

FIG. 2 is a schematic view of a process plate

Fig. 2 shows the circuit principle, and it can be seen that the circuit consists of a CPU, a high-precision AD converter, a multi-way switch and an output circuit. The corresponding N sensor chip channels of the multi-way switch, for example, the length of the ruler is 1 meter, the sensor chip interval is 10mm, 102 sensor chips are arranged, and 102 signals are correspondingly connected. The output circuit converts the result into output, and the output circuit is commonly composed of digital interfaces such as RS485 and CAN or analog interface circuits such as 0-10V and 4-20 mA.

The specific implementation mode is as follows:

in fig. 2, the sensor comprises an MCU, a multi-way switch, a high-precision AD conversion chip and an output circuit, wherein all hall sensor chips are connected to the AD conversion chip through a multi-way switch, wherein the MCU will enter a tracking measurement state after determining the initial position of the magnet according to the maximum voltage, in this state, it only measures 3 sensor induced voltages, and since the chip intervals of the measuring sensors are the same, the variation rule of the induced voltages and the relative positions is the same for the offset of the magnet positions, based on this, we have stored in the MCU a relation table between the positions and the induced voltages in advance, and the position of the current magnet deviating from the top of the chip is reversely deduced through interpolation algorithm. Obviously, when the magnet is positioned at the positive top of the chip, the induction voltage is maximum, and the farther the magnet is away, the smaller the induction voltage, when the magnet moves, the induction voltage is minimum until the magnet moves to a position between the two chips, and then the magnet moves to one side, and the chip with the maximum induction voltage is the adjacent chip. At this time, we will move the tracked 3 chips to the left or right by one chip to switch the tracked 3 chips, and use this adjacent chip as the measurement chip. For example, in fig. 1, we originally trace and measure the 3 chips of C1, C2 and C3, when the magnet moves leftwards, the magnet moves leftwards after being located at the intersection of C1 and C2, at this time we trace and measure the three chips of C0, C1 and C2, and use C1 as the calculation standard to measure the current position. In this way, the absolute position value of the magnet at any position of the rule is determined.

And an output circuit:

the output circuit is a typical circuit that can output a standard digital interface signal or an analog standard analog output signal.

Claims (1)

1. A technique of determining the amount of positional movement of a measurement target (a target having a permanent magnet embedded therein) above the measurement target by measuring voltages of a plurality of hall sensors at equal distances using a built-in interpolation algorithm.

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