Radar sensor device

Abstract

This radar sensor device comprises: a signal acquisition unit that repeatedly transmits and receives electromagnetic waves at a constant chirp period to acquire signal data; a first target detection unit; and a second target detection unit. The first target detection unit processes, for each sensing period including a first frame time composed of N consecutive chirp periods, a plurality of pieces of signal data acquired in the first frame time, thereby detecting a target operating in a first velocity range. The second target detection unit processes M pieces of signal data to be processed acquired in a second frame time to detect a target that operates within a second velocity range smaller than the first velocity range, where one of predetermined timings among the plurality of pieces of signal data acquired in the first frame time is to be processed, the sensing cycle is regarded as a chirp cycle, and M consecutive sensing cycles are defined as the second frame time.

Description

Radar sensor device

[0001] This specification discloses a radar sensor device.

[0002] Conventionally, as this type of radar sensor device, there has been proposed a device including a beat signal generation unit that repeatedly transmits and receives chirp waves to generate a beat signal, a first signal processing unit that observes the generated beat signal for a first number of observations during an observation time Tup1 and calculates a first speed from the beat signals of the first number of observations, a second signal processing unit that observes the generated beat signal for a second number of observations, which is smaller than the number obtained by multiplying the first number of observations by a time ratio (observation time Tup1 / observation time Tup2), during an observation time Tup2 that is longer than the observation time Tup1, and calculates a second speed from the beat signals of the second number of observations, and a speed determination unit that uniquely determines a measurement result of a speed represented by a resolution achieved by the second signal processing unit using the first speed calculated by the first signal processing unit (see, for example, Patent Document 1). The speed determination unit obtains a plurality of speed candidates in consideration of folding from the second speed calculated by the second signal processing unit, and determines, as the measurement result of the speed of the object, the speed candidate closer to the first speed calculated by the first speed calculation unit among the plurality of speed candidates.

[0003] Japanese Patent Application Laid-Open No. 2019-15625

[0004] In the invention described in Patent Document 1, although it is possible to measure the speed of an object with high resolution while suppressing an increase in calculation load, there is a risk of mismeasuring the speed when the objects detected by the first signal processing unit and the second signal processing unit are different objects.

[0005] The main object of the present disclosure is to achieve both the detection of an object operating within a first speed range and the detection of an object operating within a second speed range smaller than the first speed range while suppressing an increase in the amount of data.

[0006] The present disclosure has adopted the following means to achieve the above main object.

[0007] The radar sensor device of this disclosure is a radar sensor device for measuring the relative velocity of an object, and comprises: a signal acquisition unit that repeatedly transmits and receives electromagnetic waves at a constant chirp period to acquire signal data; a first object detection unit that detects an object operating in a first velocity range by processing a plurality of signal data acquired in a first frame time consisting of N (N is a natural number of 2 or more) consecutive chirp periods for each sensing period including the first frame time; and a second object detection unit that processes M of the signal data acquired in the second frame time, with one of the plurality of signal data acquired in the first frame time being the processing target, treating the sensing period as the chirp period, and treating M (M is a natural number of 2 or more) consecutive sensing periods as the second frame time, to detect an object operating in a second velocity range smaller than the first velocity range.

[0008] In the radar sensor device of this disclosure, the first object detection unit detects objects operating in a first velocity range by processing a plurality of signal data acquired in a first frame time consisting of N consecutive chirp periods for each sensing period including the first frame time. On the other hand, the second object detection unit processes one of the plurality of signal data acquired in the first frame time at a predetermined timing, treats the sensing period as a chirp period, and uses M consecutive sensing periods as the second frame time, processing M signal data acquired in the second frame time to detect objects operating in a second velocity range smaller than the first velocity range. This makes it possible to detect objects operating in the first velocity range and objects operating in the second velocity range smaller than the first velocity range simultaneously while suppressing an increase in the amount of data.

[0009] This is a schematic diagram of the robot system. This block diagram shows the electrical connection relationships between the robot body, the robot control device, and the radar sensor device. This is a flowchart illustrating an example of object detection processing. This is an explanatory diagram illustrating the first chirp frame and the second chirp frame.

[0010] Next, the forms for implementing this disclosure will be described with reference to the drawings.

[0011] Figure 1 is a schematic diagram of the robot system 1. Figure 2 is a block diagram showing the electrical connection relationship between the robot body 10, the robot control device 20, and the radar sensor device 30. As shown in the figure, the robot system 1 comprises the robot body 10, the robot control device 20 which controls the operation of the robot body 10, and the radar sensor device 30 of this embodiment which is capable of detecting objects (interfering objects) around the robot body 10.

[0012] In this embodiment, the robot body 10 is configured as a stationary robot having a multi-joint arm 12. However, the robot body 10 is not limited to a stationary robot and may be configured as a mobile robot. The mobile robot may be a transport robot such as an automated guided vehicle, in addition to a robot equipped with a multi-joint arm.

[0013] The robot body 10 comprises a base 11 and a multi-joint arm 12 mounted on the base 11. The multi-joint arm 12 has multiple arms connected in series to the base 11 via joint axes. Each joint axis is equipped with a servo motor 15 that drives the corresponding joint axis and an encoder 16 (rotary encoder) that detects the rotation angle of the corresponding servo motor 15. The robot body 10 also includes an amplifier unit 17 that applies driving current to each servo motor 15.

[0014] The robot control device 20 includes a control unit 21 configured as a microprocessor including a CPU, ROM, and RAM, and an I / O port 32 for exchanging signals with the control unit 31 of the radar sensor device 30. The robot control device 20 also receives detection signals from the encoder 16 and outputs control signals to the amplifier unit 17.

[0015] The control unit 21 of the robot control device 20 controls the operation of the robot body 10 as follows. Specifically, the control unit 21 first sets the target angle of each joint axis of the articulated arm 12 using inverse kinematics based on the target position and target orientation of the end-effector. Next, the control unit 21 obtains the current angle of each joint axis from the corresponding encoder 16 and sets the speed command value of each joint axis by feedback calculation (for example, proportional-integral calculation or proportional-integral-derivative calculation) based on the difference between the target angle and the current angle. Next, the control unit 21 sets a target speed that limits the speed of the speed command value by multiplying the speed command value by a speed limit value determined in the range of 0 (0%) to 1 (100%). For example, if the speed limit value is 1 (100%), the target speed will be the same as the speed command value. In other words, the robot speed will not be limited. Also, if the speed limit value is 0.5 (50%), the target speed will be half the speed of the speed command value. Furthermore, if the speed limit value is 0 (0%), the target speed will be 0 regardless of the speed command value. In other words, the robot control device 20 stops the operation of the robot body 10. Next, the control unit 21 calculates the current speed from the current angle of the joint axis obtained from the encoder 16, and sets the torque command value to be output from the servo motor 15 by feedback calculation (for example, proportional-integral calculation or proportional-integral-derivative calculation) based on the difference between the calculated current speed and the target speed. Then, the control unit 21 outputs a control signal to the corresponding amplifier unit 17 so that the torque corresponding to the set torque command is output from the servo motor 15.

[0016] The radar sensor device 30 in this embodiment is a safety device and is attached to the end of the articulated arm 12. The radar sensor device 30 may be attached to the base 11 of the robot body 10, or it may be installed around the robot body 10. The radar sensor device 30 detects objects (e.g., people) around the robot body 10 and measures the distance L to the object and the velocity V (relative velocity) of the object. It sets a speed limit value based on the distance L to the object, or based on a combination of the distance L to the object and the velocity V (approach velocity) of the object. The speed limit value is set so that the shorter the distance L to the object, or the higher the velocity V of the object, the greater the speed limit on the robot body 10.

[0017] The radar sensor device 30 includes a control unit 31 that controls the entire device, an I / O port 32 for exchanging signals with the control unit 21 of the robot control device 20, and a sensor unit 40 that monitors the surroundings. The control unit 31 is configured as a microprocessor including a CPU 31a, ROM 31b, and RAM 31c. The signals exchanged between the control unit 31 of the radar sensor device 30 and the control unit 21 of the robot control device 20 may be duplicated.

[0018] In this embodiment, the sensor unit 40 is configured as an FMCW (Frequency Modulation Continuous Wave) radar sensor. The sensor unit 40 includes a transmitting antenna 41 that transmits a transmit chirp, a receiving antenna 42 that receives reflected waves from an object as a receive chirp, a synthesizer 43 that generates a transmit chirp, a mixer 44 that mixes the transmit chirp and the receive chirp to generate a beat signal (signal data), and an A / D converter 45 that performs A / D conversion of the beat signal. The synthesizer 43 generates a signal that has been modulated so that its frequency changes over time as a transmit chirp. In this embodiment, the synthesizer 43 generates N transmit chirps (N is a natural number of 2 or more) that are separated by a certain transmission interval Tc (chirp period) as one chirp frame (hereinafter also referred to as the first chirp frame).

[0019] The control unit 31 performs a Fourier transform (FFT) on the beat signal generated by the sensor unit 40 to detect the distance L and velocity V to the object. The control unit 31 performs an FFT on the beat signal in units of chirps (distance FFT) to obtain a distance spectrum showing the signal strength for each frequency. Since the frequency corresponds to the distance BIN which corresponds to the detected distance from the sensor unit 40, the distance L to the object can be calculated by determining the peak of the signal strength. The control unit 31 also performs an FFT on the data after the distance FFT processing in units of chirp frames (velocity FFT) to obtain a velocity spectrum. The relative velocity V with respect to the object can be calculated by determining the peak of the signal strength in the velocity spectrum. The peak determination is performed by determining whether or not the signal strength exceeds a peak determination threshold. The peak determination threshold can be set, for example, by CFAR (Constant False Alarm Rate).

[0020] Furthermore, in this embodiment, the radar sensor device 30 is configured as a MIMO (Multi-Input Multi-Output) radar sensor and can also detect the relative angle θ of an object (the angle of the object with respect to the reference direction from the radar sensor device 30). Since the relative angle θ of an object is not central to this disclosure, a detailed explanation is omitted.

[0021] Next, the operation of the radar sensor device 30 of this embodiment will be described in detail. Figure 3 is a flowchart showing an example of object detection processing performed by the CPU 31a of the control unit 31. This processing is repeatedly performed at predetermined time intervals (for example, every few milliseconds).

[0022] In the object detection process, the CPU 31a of the control unit 31 first determines whether or not a beat signal has been input from the sensor unit 40 (S100). If the CPU 31a determines that no beat signal has been input, it terminates the object detection process. On the other hand, if the CPU 31a determines that a beat signal has been input, it increments the variable i by 1 (S102) and stores the i-th beat signal in the first memory area of ​​the RAM 31c (S104). Here, the first memory area is an area that can store up to N beat signals. The variable i is initially set to a value of 0, and is incremented by 1 each time a beat signal is input until it reaches a value of N, that is, until a beat signal equivalent to one first chirp frame has been input (stored).

[0023] Next, the CPU 31a determines whether the variable i has a value of 1 (S106). This determination determines whether the input beat signal is signal data based on the transmit / receive chirp at the beginning of the first chirp frame. If the CPU 31a determines that the variable i has a value of 1, it increments the variable k by 1 (S108) and determines whether the variable k is greater than the value M (S110). If the CPU 31a determines that the variable k is less than or equal to the value M, it stores the k-th beat signal in the second memory area of ​​the RAM 31c (S112) and terminates the object detection process. If the CPU 31a determines that the variable k is greater than the value M, it overwrites the oldest data in the second memory area of ​​the RAM 31c with the k-th beat signal (S114) and terminates the object detection process. Here, the second memory area is an area that can store up to M beat signals. The variable k is initially set to a value of 0 and is incremented by 1 each time the beat signal at the beginning of the first chirp frame is input (stored). In the second memory area, once the maximum number of beat signals (M) has been stored, subsequent beat signals are stored in such a way that they overwrite the oldest data. As the processes S110 to S114 are repeated, the second memory area will store M beat signals acquired in M ​​consecutive first chirp frames.

[0024] In S106, if the CPU 31a determines that variable i is not valued at 1, it determines whether variable i is valued at N (S116). If the CPU 31a determines that variable i is not valued at N, that is, greater than value 1 and less than value N, it terminates the object detection process. On the other hand, if the CPU 31a determines that variable i is valued at N, it determines that a beat signal equivalent to one first chirp frame is stored in the first memory area and starts the following detection process (S118).

[0025] In the detection process, the CPU 31a performs distance FFT processing on each of the N beat signals in the first memory area to measure the distance L (first distance L1) of the object, and also performs velocity FFT processing on the data after the distance FFT processing in units of the first chirp frame to measure the velocity V (first velocity V1) of the object (S120). Next, the CPU 31a resets the variable i to value 0 and clears the first memory area (S122). Then, the CPU 31a determines whether the variable k is greater than or equal to the value M (S124). When the CPU 31a determines that the variable k is greater than or equal to the value M, it determines that the second memory area contains M beat signals acquired in M ​​consecutive first chirp frames, and performs distance FFT processing on each of the M beat signals in the second memory area to measure the distance L of the object (second distance L2). At the same time, it performs velocity FFT processing on the data after the distance FFT processing in units of second chirp frames, which have a longer frame time than the first chirp frames, to measure the velocity V of the object (second velocity V2) (S126). As a result, the CPU 31a can measure the second velocity V2 of the object with finer velocity resolution than the first velocity V1. In this embodiment, the measurement of the second velocity V2 is for detecting slight human movements such as breathing. When measuring the second velocity V2, the CPU 31a discards the zero velocity component in order to distinguish and detect a stationary person from an object. On the other hand, when measuring the first velocity V1, the CPU 31a does not discard the zero velocity component. In this embodiment, the CPU 31a also performs pairing in the detection process by comparing a first distance L1 with a second distance L2, or comparing a first velocity V1 with a second velocity V2, thereby considering objects with approximately the same distances L1 and L2 or velocities V1 and V2 as the same object. If the CPU 31a also measures the angle θ of the object, it may also consider the angle matching when performing pairing. In S124, if the CPU 31a determines that the variable k is less than the value M, it skips S126. Then, the CPU 31a waits for the detection processing time Td to elapse (S128) and terminates the object detection process.

[0026] In this way, the CPU 31a uses the transmission interval Tc of the transmitted chirp as the chirp period and considers N consecutive transmitted and received chirps as the first chirp frame. It stores the N beat signals acquired during the time of the first chirp frame (first chirp frame time Tf1) in the first memory area and measures the first velocity V1 of the object from the N beat signals in the first memory area. Furthermore, the CPU 31a considers the sensing period T, which consists of the first chirp frame time Tf1 and the detection processing time (detection processing time Td), as the chirp period and considers M consecutive sensing periods T as the time of the second chirp frame (second chirp frame time Tf2). It stores the M beat signals acquired in each of the M consecutive first chirp frames in the second memory area and measures the second velocity V2 of the object from the M beat signals in the second memory area. As a result, the radar sensor device 30 of this embodiment can simultaneously detect objects with a normal speed (first speed V1) and objects with a weak speed (second speed V2). In other words, by appropriately determining the first chirp frame time Tf1 and the second chirp frame time Tf2, the radar sensor device 30 of this embodiment can detect a person moving at a normal speed as an object, and can also distinguish and detect a person who is stationary with weak movements such as breathing from an object. As a result, the radar sensor device 30 can be effectively used as a safety device.

[0027] Here, the velocity resolution V_res of the radar sensor device 30 is inversely proportional to the chirp frame time Tf, as shown in equation (1), where λ is the wavelength and Tf is the chirp frame time. Therefore, by increasing the chirp frame time Tf, the resolution can be made finer. On the other hand, the maximum detection speed V_max is determined by the number of chirp transmissions and receptions N per chirp frame time Tf, as shown in equation (2). For example, if the number of chirp transmissions and receptions N is kept constant and only the chirp frame time Tf is doubled, the velocity resolution V_res becomes twice as fine (half), but the maximum detection speed V_max becomes half. For this reason, in order to double the velocity resolution V_res without changing the maximum detection speed V_max, not only the chirp frame time Tf but also the number of transmissions and receptions N must be doubled, which leads to an increase in the amount of data.

[0028] V_res=λ / 2Tf…(1) V_max=V_res×N / 2…(2)

[0029] For example, if a 60 GHz radar is used as the radar sensor device 30, and the wavelength is 5 mm, in order to detect weak movements of about 2 mm / s, such as human respiration, it is necessary to set the chirp frame time Tf to about 2 seconds and the velocity resolution to about 1.25 mm / s. On the other hand, in order to stably detect human movement speeds up to a typical 2000 mm / s, the number of transmissions and receptions N per chirp frame time Tf needs to be 3200 or more, which results in an enormous amount of data and is not practical. Since object detection is performed by array calculations using FFT, the increase in the amount of data leads not only to insufficient memory but also to a prolongation of the sensing period T (detection process). In contrast, in this embodiment, it is sufficient to provide a first memory area that stores N beat signals to detect the general human motion speed (first velocity V1) and a second memory area that stores M beat signals for each sensing period T to detect the weak human movement (second velocity V2). Therefore, it is possible to suppress the increase in the amount of data while simultaneously detecting objects with general velocity and objects with weak velocity.

[0030] Here, the correspondence between the main elements of the embodiment and the main elements of the present disclosure as described in the claims will be explained. Specifically, the radar sensor device 30 of this embodiment corresponds to the object detection device of the present disclosure, the sensor unit 40 is an example of a signal acquisition unit, the CPU 31a that executes object detection processing S100 to S106 and S116 to S122 is an example of a first object detection unit, and the CPU 31a that executes object detection processing S100 to S114, S116, S124, and S126 is an example of a second object detection unit. In addition, the RAM 31c is an example of a storage unit.

[0031] It goes without saying that this disclosure is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of this disclosure.

[0032] For example, in the embodiment described above, the second chirp frame used a beat signal acquired based on the transmit / receive chirp at the beginning of the first chirp frame. However, any beat signal acquired at a different timing may be used, as long as it is acquired at the same timing for each first chirp frame.

[0033] Furthermore, in the embodiment described above, the CPU 31a stores up to M beat signals acquired at predetermined timings for each sensing period T in the second memory area, then overwrites subsequent beat signals in order from the oldest data, and processes the M beat signals in the second memory area for each sensing period T to measure the second velocity V2 of the object. However, the CPU 31a may also measure the second velocity V2 of the object for each second chirp frame time Tf2 by repeating a measurement process, which involves storing up to M beat signals acquired for each sensing period T in the second memory area, processing the M beat signals in the second memory area to measure the second velocity V2 of the object, and a reset process, which involves resetting the second memory area, for each second chirp frame time Tf2.

[0034] As described above, in the radar sensor device of this disclosure, the first object detection unit detects objects operating in a first velocity range by processing a plurality of signal data acquired in a first frame time consisting of N consecutive chirp periods for each sensing period including the first frame time. On the other hand, the second object detection unit processes one of the plurality of signal data acquired in the first frame time at a predetermined timing, treats the sensing period as a chirp period, and uses M consecutive sensing periods as the second frame time, processing M signal data acquired in the second frame time to detect objects operating in a second velocity range smaller than the first velocity range. This makes it possible to detect objects operating in the first velocity range and objects operating in the second velocity range smaller than the first velocity range simultaneously while suppressing an increase in the amount of data.

[0035] In the radar sensor device of this disclosure, the second object detection unit may include a storage unit for storing the signal data, and after storing up to M of the signal data to be processed acquired at each sensing cycle in the storage unit, it may overwrite the oldest data in order and process the M of the signal data to be processed stored in the storage unit at each sensing cycle. In this way, the second object detection unit can detect an object operating in the second velocity range at the same sensing cycle as the first object detection unit while suppressing an increase in the amount of data stored in the storage unit. In this case, the second object detection unit may store the signal data acquired based on electromagnetic waves transmitted and received at the beginning of the sensing cycle as the data to be processed in the storage unit.

[0036] Furthermore, in the radar sensor device of this disclosure, the first speed range may be a speed range capable of detecting a moving person, and the second speed range may be a speed range capable of detecting a stationary person in distinction from an object. In this way, when the radar sensor device of this disclosure is used as a safety device, it becomes possible to detect people in the surrounding area more reliably, thereby enhancing safety.

[0037] This disclosure can be used in industries such as the manufacturing of radar sensor devices.

[0038] 1 Robot system, 10 Robot body, 11 Base, 12 Articulated arm, 15 Servo motor, 16 Encoder, 17 Amplifier unit, 20 Robot control device, 21 Control unit, 22 I / O port, 30 Radar sensor device, 31 Control unit, 31a CPU, 31b ROM, 31c RAM, 32 I / O port, 40 Sensor unit, 41 Transmitting antenna, 42 Receiving antenna, 43 Synthesizer, 44 Mixer, 45 A / D converter.

Claims

1. A radar sensor device for measuring the relative velocity of an object, comprising: a signal acquisition unit that repeatedly transmits and receives electromagnetic waves at a constant chirp period to acquire signal data; a first object detection unit that detects an object operating in a first velocity range by processing a plurality of signal data acquired in a first frame time consisting of N (N is a natural number of 2 or more) consecutive chirp periods for each sensing period including the first frame time; and a second object detection unit that processes M of the signal data acquired in the second frame time, with one of the plurality of signal data acquired in the first frame time being the processing target, treating the sensing period as the chirp period, and using M (M is a natural number of 2 or more) consecutive sensing periods as the second frame time, to detect an object operating in a second velocity range smaller than the first velocity range.

2. A radar sensor device according to claim 1, comprising a storage unit for storing the signal data, wherein the second object detection unit stores up to M of the signal data to be processed acquired at each sensing cycle in the storage unit, overwrites them in order from the oldest data, and processes the M of the signal data to be processed stored in the storage unit at each sensing cycle.

3. A radar sensor device according to claim 2, wherein the second object detection unit stores signal data acquired based on electromagnetic waves transmitted and received at the beginning of the sensing cycle in the storage unit as the object to be processed.

4. A radar sensor device according to any one of claims 1 to 3, wherein the first speed range is a speed range capable of detecting a moving person, and the second speed range is a speed range capable of detecting a stationary person separately from an object.

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