Rotational speed detection device

Abstract

To provide a rotational speed detection device which has a simple and inexpensive constitution, and which further, can be easily additionally installed to an existing device or equipment.SOLUTION: A rotational speed detection device comprises: an index part 8a provided on a rotary body 8; sensors 9a, 9b that output a detection signal according to approach and separation by the index part 8a; and a computing unit that performs calculation of rotational speed of the rotary body 8 based on the detection signal. The rotational speed detection device includes a first sensor 9a and a second sensor 9b that are arranged spaced apart in a rotational direction. The first sensor 9a and the second sensor 9b are provided at positions where the timings of detecting the index part 8a are different according to a rotational direction of the rotary body 8. The computing unit obtains a rotational direction of the rotary body 8 on the basis of a time lag between a detection signal by the first sensor 9a and a detection signal by the second sensor 9b.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a device for detecting the rotational speed of a rotating body that rotates while traveling in order to determine the traveling speed of a traveling body such as a small electric towing vehicle, and in particular to a device that can detect the rotation direction as well as the rotational speed. [Background technology]

[0002] An example of this type of detection device is described in Patent Document 1. This device is a magnetic detection device that includes a magnetic rotating plate, with S and N poles arranged alternately in the rotational direction, attached to an object (rotating body) whose rotation speed is to be detected, and a rotation sensor facing the magnetic rotating plate. When the magnetic rotating plate rotates together with the rotating body, each magnetic pole passes in front of the rotation sensor, generating a pulse train signal. The rotation speed is detected by counting these pulses. The device in Patent Document 1 also includes a second magnetic pole rotating plate, whose magnetic poles are shifted in the rotational direction relative to the first magnetic pole rotating plate, and a second rotation sensor facing the second magnetic pole rotating plate. The device is configured to detect the rotation direction based on the phase shift between the pulse train signals obtained by the first rotation sensor and the second rotation sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 09-159684 Summary of the Invention [Problem to be solved by the invention]

[0004] The device described in Patent Document 1 detects the rotation speed of a rotating body based on a pulse train signal obtained by a rotation sensor, where the pulse width or the number of pulses per unit time generated by each magnetic pole, arranged at regular intervals, crossing the front side of the rotation sensor corresponds to the rotation speed of the rotating body. The pulse train signals are out of phase with each other by shifting the first and second magnetic pole rotating plates in the rotation direction. Since this shift corresponds to the rotation direction of the rotating body, the device described in Patent Document 1 detects the rotation direction based on the pulse train signal obtained by the two magnetic pole rotating plates and the rotation sensor. Thus, to detect the rotation direction as well as the rotation speed, the device described in Patent Document 1 requires two pairs of magnetic pole rotating plates and opposing rotation sensors. In other words, the device described in Patent Document 1 requires at least two identical magnetic rotating plates and rotation sensors, resulting in a complex, large-scale, and expensive configuration. Furthermore, adding the device to an existing device or equipment requires additional space, which may ultimately make it impossible to add the device.

[0005] The present invention has been made in light of the above technical problems, and aims to simplify and reduce the cost of a rotational speed detection device that can detect both the rotational speed and the direction of rotation, and further to make it possible to easily add the device to existing devices and equipment. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the present invention provides a rotational speed detection device comprising an indicator portion provided on a rotating body that is the detection object, a sensor that outputs a detection signal when the indicator portion approaches and moves away from the rotating body, and a calculator that calculates the rotational speed of the rotating body based on the detection signal, wherein the sensor includes a first sensor and a second sensor that are arranged apart in the rotational direction of the rotating body, and the first sensor and the second sensor are arranged at positions where the timing of detecting the indicator portion differs depending on the rotational direction of the rotating body, and the calculator is further configured to determine the rotational direction of the rotating body based on the time difference between the detection signal from the first sensor and the detection signal from the second sensor.

[0007] In the present invention, the indicator portions may be arranged in a row at a constant pitch in the rotational direction on the rotating body, and the distance between the first sensor and the second sensor in the rotational direction may be a dimension that is an integer multiple of the pitch of the indicator portions plus or minus a dimension that is different from half the pitch.

[0008] In the present invention, the indicator portion may be a protrusion protruding from the rotating body, and the first sensor and the second sensor may be configured so that the voltage changes as the protrusion approaches and moves away from each other.

[0009] In the present invention, the first sensor and the second sensor may be configured to generate a signal in response to a change in magnetic flux caused by the approach of the protrusion.

[0010] In the present invention, the indicator portion may be a heat dissipation fin provided on the rotating body. [Effects of the Invention]

[0011] According to the present invention, as the rotating body rotates, the indicator portion approaches and moves away from the sensor, causing the sensor to output a detection signal. The first sensor and the second sensor are provided in relative positions where the timing at which they detect the indicator portion differs depending on the rotation direction of the rotating body, and the rotation direction can be detected based on the difference in detection timing. Therefore, in the present invention, the rotation direction can be detected by arranging the first sensor and the second sensor, which have the same configuration, at a distance as described above, so the indicator portion can be common to the first sensor and the second sensor. As a result, it is possible to provide a rotation speed detection device that requires fewer components and is simple in configuration and inexpensive.

[0012] In addition, in the present invention, the indicator portions may be arranged in a line at a constant pitch in the rotational direction. In this case, the detection signal is a pulse train signal consisting of a series of pulses. The pulse width or the number per unit time corresponds to the rotational speed, and the calculator calculates the rotational speed based on the detection signal. Meanwhile, the first and second sensors are arranged apart in the rotational direction of the rotor, and the distance between them is offset by a distance that is less than half the pitch, relative to an integer multiple of the pitch of the indicator portions. Therefore, even though the detection signals from the first and second sensors are output in response to the indicator portions, there is a time delay corresponding to the distance that is less than half the pitch. This delay varies depending on the rotational direction of the rotor, and the calculator calculates the rotational direction of the rotor based on the time delay between the detection signals from the first and second sensors. Therefore, in the present invention, by arranging the first sensor and second sensor having the same configuration at a distance as described above, the direction of rotation can be detected, and the indicator portion can be common to the first sensor and the second sensor. As a result, the number of required components can be reduced, making it possible to provide a rotation speed detection device that is simple in configuration and inexpensive.

[0013] Furthermore, in the present invention, the indicator part may be a protrusion to which the sensor responds or a heat dissipation fin arranged at a fixed pitch, and therefore can be easily added to an existing rotating body equipped with these protrusions or heat dissipation fins without requiring any major modifications to the equipment. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing an example in which the present invention is applied to a rotational speed detection device for a small electric towing vehicle, and is a schematic side view of the small electric towing vehicle. FIG. [Figure 2] FIG. 2 is a schematic rear view of the small electric towing vehicle as seen from the rear. [Figure 3] FIG. 2 is a partial schematic diagram showing the relative arrangement of the rear wheels, motor, rotating body, and sensor. [Figure 4] FIG. 10 is an explanatory diagram for explaining the positional relationship between two sensors and an indicator portion. [Figure 5] FIG. 4 is a waveform diagram showing an example of detected waveforms obtained by two sensors. DETAILED DESCRIPTION OF THE INVENTION

[0015] Next, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the embodiment described below is merely an example of how the present invention can be implemented, and is not intended to limit the present invention.

[0016] The rotational speed detection device according to the present invention can be used, for example, as a device for detecting the traveling speed of a vehicle (mobile object), and an example thereof will be described below. Figures 1 and 2 show an example in which the rotational speed detection device according to the present invention is mounted on a small electric tow vehicle (hereinafter simply referred to as vehicle) 1 that travels within a designated area such as a factory (not shown). The vehicle 1 shown here is configured so that rear wheels 2 are driven by a motor 3, and is capable of manual driving, where the vehicle is operated by a driver (not shown), and automatic driving, where the vehicle is operated according to a pre-prepared program. Therefore, although not specifically shown, the vehicle is equipped with devices for traveling that are equipped on a typical vehicle, such as a steering device, an acceleration / deceleration device, and a braking device.

[0017] In addition, the vehicle is equipped with devices for autonomous driving, such as a three-dimensional lidar (3D LIDAR) 4 for detecting the presence and distance of surrounding facilities and equipment, a computer 5 for processing data input from the 3D LIDAR 4, and a programmable logic controller (PLC) 6 for controlling driving. Furthermore, a motor controller 7 is provided to control the motor 3, and is configured to control the motor 3 in response to acceleration and deceleration operations during manual driving, and based on control command signals from the PLC 6 during autonomous driving.

[0018] In the case of manual driving, the driver is responsible for recognizing the vehicle 1's speed and whether it is moving forward or backward and for operating the vehicle, but in the case of automatic driving, it is necessary to grasp the speed and whether it is moving forward or backward on behalf of the driver, and a rotational speed detection device is provided for this detection. The vehicle 1 basically drives the motor 3 in response to a command signal to travel (forward or backward) at a commanded speed and in a commanded direction, but if, for example, there is a slope on the road surface and the driving force of the motor 3 is insufficient, the vehicle may not move in the direction commanded by the command signal and may end up moving in the opposite direction. In such a case, the vehicle 1 may be automatically stopped or the output torque of the motor 3 may be increased, so it is necessary to detect the direction of travel.

[0019] For this purpose, as an example, a rotational speed detection device according to an embodiment of the present invention is configured to detect the rotation of a rotating body that rotates together with the rear wheels 2, which are drive wheels, when the vehicle 1 is traveling, and to detect the direction of rotation (the direction of travel or movement in the case of the vehicle 1). In the example shown in FIGS. 1 and 2, a sensor 9 that outputs a detection signal in response to the rotation of the rotating body 8 is provided on the outer periphery of the motor 3 (more precisely, on the outer periphery of the rotating body 8 that rotates together with the motor 3). The sensor 9 is a detector that outputs a detection signal in response to a plurality of indicators 8a provided on the rotating body 8 at a constant pitch in the rotational direction of the rotating body 8. For example, the sensor 9 may be an electromagnetic pickup that generates a signal in response to changes in magnetic flux. In the example shown in the figures, the sensor 9 is composed of two detectors, a first sensor 9a and a second sensor 9b, arranged facing the rotating body 8, as shown in FIGS. 3 and 4.

[0020] The first sensor 9a and the second sensor 9b are disposed apart from each other in the rotational direction of the rotor 8, and the interval L between them is set so that the timing at which the first sensor 9a and the second sensor 9b detect the indicator portions 8a of the rotor 8 is shifted (so that there is a time lag). Specifically, if the pitch, which is the distance between the indicator portions 8a in the rotational direction (circumferential direction), is "P," the interval L measured in the rotational direction (circumferential direction) between the first sensor 9a and the second sensor 9b is an integer multiple of the pitch P plus or minus a distance shifted from half the pitch P (P / 2). Explaining this in terms of a central angle, since multiple n indicator portions 8a are provided at equal intervals at a constant pitch P on the outer periphery of the rotor 8, the central angle θ (angle around the center O of the rotor 8) corresponding to the distance between the indicator portions 8a is expressed as an angle (2π / n) obtained by dividing "2π" by the number n of indicator portions 8a, as shown in FIG. 4. Figure 4 shows an example in which the second sensor 9b is approximately three pitches (3P) away from the first sensor 9a, and the distance (central angle) between them is set to a central angle (3θ-θ / 3) obtained by subtracting an angle (e.g., θ / 3) that is half the angle θ corresponding to the pitch P from an angle (e.g., 3θ) that is an integer multiple of the pitch P.

[0021] 4, when the indicator portion 8a approaches the first sensor 9a and the first sensor 9a outputs a detection signal, the indicator portion 8a is far from the second sensor 9b, so the second sensor 9b does not output a detection signal. As the rotating body 8 rotates from this state, the indicator portion 8a moves away from the first sensor 9a and another indicator portion 8a approaches the second sensor 9b, causing the second sensor 9b to respond to the indicator portion 8a and output a detection signal. In this way, the first sensor 9a and the second sensor 9b are configured to output detection signals at different times.

[0022] Regarding the indicator 8a, the indicator 8a may be any element that the sensor 9 (9a, 9b) senses and outputs a detection signal. If the sensor 9 (9a, 9b) is an electrical or magnetic detector, such as an electromagnetic pickup, the indicator 8a may be a metallic protrusion. If the sensor 9 (9a, 9b) is an optical detector, the indicator 8a may be a reflective element that reflects visible light or light of a specific wavelength differently from other elements. In the example shown in FIG. 3 or 4, the indicator 8a is composed of heat dissipation fins that protrude outward in the radial direction and are provided at a constant pitch P in the rotational direction on the outer periphery of the rotor 8. Therefore, the first sensor 9a and the second sensor 9b are positioned close to the tips of the heat dissipation fins. As the rotor 8 rotates, the heat dissipation fins approach and move away from the first sensor 9a and the second sensor 9b, causing the first sensor 9a and the second sensor 9b to output a detection signal.

[0023] In the embodiment described here, the detection signal generated by the sensor 9 (9a, 9b) is a pulse train signal, and the pulse width, pulse interval, or number of detected pulses per unit time corresponds to the rotational speed of the rotating body 8. That is, when the rotational speed is slow, the pulse width and pulse interval become wider, and the number of pulses per unit time becomes smaller. Conversely, when the rotational speed is fast, the pulse width and pulse interval become narrower, and the number of pulses per unit time becomes larger. Furthermore, because the interval between the first sensor 9a and the second sensor 9b is set as described above, there is a timing difference between the detection signals obtained by these first sensor 9a and second sensor 9b, and the length of this difference corresponds to the rotational direction of the rotating body 8.

[0024] The above-mentioned PLC 6 is connected to sensors 9 (9a, 9b), and is configured to determine the rotation speed and rotation direction based on detection signals (pulse train signals) input from the sensors 9 (9a, 9b). Therefore, the PLC 6 corresponds to the computing unit in the embodiment of the present invention.

[0025] The PLC 6 is an electronic control device mainly composed of a microcomputer, configured to perform calculations in accordance with a pre-prepared program using input data and pre-stored data. In this embodiment of the present invention, the PLC 6 is particularly configured to calculate the traveling speed of the vehicle 1 and determine whether the vehicle is moving forward or backward. Regarding its traveling speed calculation function, the aforementioned rotating body 8 is configured to rotate together with the rear wheels 2, so there is a correspondence between the traveling speed and the rotational speed of the rotating body 8. Therefore, the traveling speed is calculated as the rotational speed of the rotating body 8. As described above, the detection signal of the sensor 9 (9a, 9b) is a pulse train signal, and the number of pulses detected per unit time (i.e., the number of indicator portions 8a) corresponds to the rotational speed of the rotating body 8. Therefore, the vehicle speed is calculated by counting the number of pulses per unit time. The PLC 6 calculates the traveling speed by counting the number of pulses per unit time based on the detection signal input from the first sensor 9a or the detection signal input from the second sensor 9b, or the detection signals input from both sensors 9a and 9b.

[0026] Meanwhile, forward and reverse travel is determined by comparing the detection signal from the first sensor 9a with the detection signal from the second sensor 9b. Figure 5 shows a detection waveform A obtained by the first sensor 9a and a detection waveform B obtained by the second sensor 9b. In the example shown here, the detection value (e.g., voltage) decreases as the indicator part 8a approaches and moves away from each of the first sensor 9a and the second sensor 9b, i.e., crosses over them. Therefore, each of the detection waveforms A and B is a waveform in which valleys occur at a period T that corresponds to the pitch P of the indicator part 8a and the rotational speed of the rotor 8 (the traveling speed of the vehicle 1).

[0027] As described above, the first sensor 9a and the second sensor 9b are arranged offset in the rotational direction of the rotor 8. Therefore, for example, at time t0, when one of the indicator portions 8a approaches the first sensor 9a and the detection value of the first sensor 9a drops, both indicator portions 8a are out of alignment with the tip of the second sensor 9b. That is, at time t0, the detection value in detection waveform A drops to form a valley, while the detection value in detection waveform B is high. As the rotor 8 rotates from this state, the indicator portion 8a moves away from the first sensor 9a, and its detection value increases. In contrast, the indicator portion 8a gradually approaches the second sensor 9b, and at time t1, when the indicator portion 8a faces the tip of the second sensor 9b, the detection value of the second sensor 9b drops, and a valley appears in detection waveform B.

[0028] The time difference ΔT between time t0 and time t1 corresponds to the difference in the distance between the first sensor 9a and the second sensor 9b (the angle between them) relative to the pitch P of the indicator portion 8a or an integral multiple thereof (central angle). For example, in FIG. 4, when the rotating body 8 is rotating counterclockwise, the time difference ΔT is equivalent to θ / 3. Conversely, when the rotating body 8 is rotating clockwise, the time difference ΔT is equivalent to 2θ / 3 (= θ - θ / 3). Ultimately, the length of the time difference ΔT between the time when the detection value in detection waveform A reaches a predetermined value and the time when detection waveform B reaches a value corresponding to that predetermined value corresponds to the rotation direction of the rotating body 8. Therefore, the PLC 6 calculates this time difference ΔT and determines the rotation direction of the rotating body 8, i.e., whether the vehicle 1 is moving forward or backward, based on the calculated value. That is, in the example shown in FIG. 4, if the time difference ΔT is a length equivalent to θ / 3, it is determined that the rotating body 8 is rotating counterclockwise, and conversely, if the time difference ΔT is a length equivalent to 2θ / 3, it is determined that the rotating body 8 is rotating clockwise.

[0029] The determination of forward or reverse movement based on the time difference ΔT described above is made possible by the fact that the distance between the two sensors 9a, 9b is shifted with respect to the pitch P of the indicator portion 8a or a dimension (central angle) that is an integral multiple thereof, and the amount of this shift is different from half the pitch P of the indicator portion 8a. Therefore, instead of determining whether forward or reverse movement is made based on whether the time difference ΔT described above matches the length corresponding to the central angle (θ / 3 or 2θ / 3) that corresponds to the amount of shift, it is also possible to determine whether forward or reverse movement is made based on whether the time difference ΔT is longer than the length corresponding to half the pitch P (θ / 2).

[0030] As described above, in the embodiment of the present invention, the rotation direction of a rotating body 8, i.e., whether the vehicle 1 is moving forward or backward, is determined by using two sensors 9a, 9b to detect a single rotating body 8 on which a plurality of indicator portions 8a are arranged at a constant pitch P in the circumferential direction, and therefore the configuration can be simplified and the device can be made inexpensive compared to providing a detection object (indicator portion) for each sensor 9a, 9b. Furthermore, because the indicator portions 8a can be existing members or parts such as heat dissipation fins, the rotation speed detection device in the embodiment of the present invention can be easily added to an existing device or equipment, which also contributes to a simplified and inexpensive configuration.

[0031] The present invention is not limited to the above-described embodiment, and can be used not only for detecting the traveling speed or forward / reverse movement of a small electric towing vehicle, but also for detecting the rotational speed and direction of a general rotating body. Furthermore, the indicator may be configured with multiple indicators arranged at a constant pitch, or may be a single indicator with two sensors that respond at different times. In this case, the distance between the two sensors may be set to a distance that is shifted from half the circumference of the rotating body. By doing so, the time from when one sensor detects the indicator to when the other sensor detects the indicator varies depending on the direction of rotation, and the direction of rotation can be determined based on this difference in detection timing. [Explanation of symbols]

[0032] 1 vehicle 2 rear wheels 3 motors 4. 3D Lidar 5. Computer 6 Programmable Logic Controller (PLC) 7 Motor Controller 8 Rotating Body 8a Index section 9, 9a, 9b Sensors ΔT time difference θ center angle A Detected waveform B Detected waveform L spacing Pitch T period

Claims

1. A rotation speed detection device comprising: an indicator provided on a rotating body that is a detection target; a sensor that outputs a detection signal when the indicator approaches and moves away from the rotating body; and a calculator that calculates the rotation speed of the rotating body based on the detection signal, the sensor includes a first sensor and a second sensor that are spaced apart in the rotation direction of the rotating body, the first sensor and the second sensor are provided at positions where the timing of detecting the indicator portion differs depending on the rotation direction of the rotating body, The computing unit is further configured to determine the rotation direction of the rotating body based on a time difference between the detection signal from the first sensor and the detection signal from the second sensor. A rotation speed detection device characterized by:

2. 2. The rotational speed detection device according to claim 1, a plurality of the indicator portions are provided on the rotating body at a constant pitch in the rotation direction, The distance between the first sensor and the second sensor in the rotation direction is a dimension obtained by adding or subtracting a dimension that is different from half the pitch to a dimension that is an integer multiple of the pitch of the indicator portion. A rotation speed detection device characterized by:

3. 3. The rotation speed detection device according to claim 1, the indicator portion is a protrusion protruding from the rotating body, The first sensor and the second sensor are configured such that a voltage thereof changes as the protrusions approach and move away from each other. A rotation speed detection device characterized by:

4. 4. The rotational speed detection device according to claim 3, The first sensor and the second sensor are configured to generate a signal in response to a change in magnetic flux caused by the approach of the protrusion. A rotation speed detection device characterized by:

5. 3. The rotation speed detection device according to claim 1, The indicator portion is a heat dissipation fin provided on the rotating body. A rotation speed detection device characterized by:

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