Object detection device, robot system, and failure diagnosis method

Abstract

This object detection device comprises: a sensor unit that transmits and receives electromagnetic waves; a determination unit that acquires an intensity at each distance on the basis of an output signal from the sensor unit, calculates an intensity differential, which is the difference between the acquired intensity and a predetermined comparison intensity, at each distance, and detects an intensity differential peak for the distances to determine the presence or absence of an object; and a diagnosis unit that diagnoses a failure of the object detection device by comparing the intensity differential and a threshold value having the reverse sign.

Description

Object detection device, robot system, and fault diagnosis method

[0001] This specification discloses an object detection device, a robot system, and a fault diagnosis method.

[0002] A measuring device has been proposed that includes a reflecting object observation unit that irradiates a detection target area with electromagnetic waves, receives reflected waves from a reflector installed at a predetermined position, and observes the distance to the reflector and the reflection intensity from the received reflected waves, a determination processing unit that determines the presence or absence of an obstacle based on fluctuations in the distance and reflection intensity output from the reflecting object observation unit, and a self-diagnosis unit that determines an abnormality in the device (see, for example, Patent Document 1). The self-diagnosis unit inputs the distance to the reflection position and the reflection intensity from the determination processing unit, and determines that an abnormality has occurred in the measuring device if the reflection intensity deviates from a predetermined range determined in accordance with natural fluctuations for a certain period of time and the distance to the reflection position deviates from the detection target area.

[0003] Japanese Patent Application Laid-Open No. 2005-233615

[0004] The device described in Patent Document 1 determines that an abnormality has occurred in the measurement device when the reflection intensity deviates from a predetermined range for a certain period of time and the distance to the reflection position deviates from the detection target area, but if the reflection intensity decreases to the point where it is difficult to observe the distance, it is not possible to diagnose an abnormality in the measurement device. Furthermore, it is desirable to diagnose an abnormality using as simple a process as possible.

[0005] A main object of the present disclosure is to more reliably self-diagnose a fault in an object detection device using simple processing.

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

[0007] The object detection device of the present disclosure is an object detection device that detects objects, and comprises: a sensor unit that transmits and receives electromagnetic waves; a determination unit that acquires intensity for each distance based on an output signal from the sensor unit, calculates a differential intensity, which is the difference between the acquired intensity and a predetermined comparison intensity, for each distance, and determines whether or not the object is present by detecting a peak of the differential intensity with respect to the distance; and a diagnosis unit that diagnoses a malfunction of the object detection device by comparing the differential intensity with a threshold value of the opposite sign.

[0008] In the object detection device disclosed herein, a differential intensity is calculated for each distance, which is the difference between the intensity for each distance acquired based on the output signal from the sensor unit and a predetermined comparison intensity, and the presence or absence of an object is determined by detecting the peak of the differential intensity for each distance. For example, by measuring background noise in advance and setting the measured intensity as the comparison intensity, the influence of the background noise on the intensity can be eliminated, allowing for accurate object detection. Furthermore, while the intensity acquired based on the output signal from the sensor unit decreases due to a sensor failure, the comparison intensity remains constant, so the differential intensity appears with an inverted sign due to a sensor failure. Therefore, by comparing the differential intensity with a threshold value of an inverted sign, the object detection device can more reliably self-diagnose a failure with simple processing.

[0009] The robot system of the present disclosure comprises: a robot; an object detection device provided on the robot, the object detection device having a sensor unit that transmits and receives electromagnetic waves, a determination unit that acquires intensity for each distance based on an output signal from the sensor unit, calculates a differential intensity, which is the difference between the acquired intensity and a predetermined comparison intensity, for each distance, and determines the presence or absence of the object by detecting a peak of the differential intensity with respect to the distance, and a diagnosis unit that diagnoses a malfunction of the sensor unit by comparing the differential intensity with a threshold value of an opposite sign; and a robot control device that stops the operation of the robot when a malfunction of the sensor unit is diagnosed by the diagnosis unit while the robot is operating.

[0010] The robot system of the present disclosure includes the object detection device of the present disclosure, and therefore can more reliably self-diagnose the object detection device with simple processing. Furthermore, if a malfunction of the object detection device is diagnosed, the robot is stopped, thereby ensuring the safety of the robot.

[0011] The present disclosure may also be in the form of a fault diagnosis method.

[0012] 5A is a schematic diagram of a robot system according to the present embodiment; FIG. 5B is a block diagram showing the electrical connection relationship between a robot main body, a robot control device, and a safety device; FIG. 3A is an explanatory diagram showing how a peak is determined from the signal strength for each distance BIN in a normal state, and FIG. 3B is an explanatory diagram showing how a peak is determined from the signal strength for each distance BIN in a fault state; FIG. 5A is an explanatory diagram showing an example of signal strength (distance spectrum) for each distance BIN acquired from a sensor unit; FIG. 5B is an explanatory diagram showing an example of comparison strength for each distance BIN that is set in advance; and FIG. 5C is an explanatory diagram showing an example of differential strength for each distance BIN; FIG. 5B is an explanatory diagram showing an example of differential strength for each distance BIN in a fault state; and FIG. 5C is an explanatory diagram showing an example of differential strength obtained when an object is present at an extremely short distance; and FIG. 5C is a flowchart showing object detection processing of a modified example; and FIG. 5A is a schematic diagram of a robot system according to another embodiment;

[0013] Next, embodiments of the present disclosure will be described with reference to the drawings.

[0014] Fig. 1 is a schematic diagram of a robot system 1 according to this embodiment. Fig. 2 is a block diagram showing the electrical connection relationship between a robot main body 10, a robot controller 20, and a safety device 30. As shown in the figure, the robot system 1 according to this embodiment includes the robot main body 10, the robot controller 20 that controls the operation of the robot main body 10, and a robot safety device 30 that can detect interfering objects around the robot main body 10.

[0015] The robot body 10 is a work robot that performs a specified task, and examples thereof include a processing robot that processes a workpiece with a tool, a transport robot that grasps a workpiece with a chuck and transports it to another position, and an assembly robot that grasps a workpiece with a chuck and assembles it to an object.

[0016] The robot main body 10 has a base 11 and an articulated arm 12 mounted on the base 11. The articulated arm 12 has a plurality of arms connected in series to the base 11 via joint shafts. Each joint shaft is provided with a servo motor 15 that drives the corresponding joint shaft, and an encoder 16 (rotary encoder) that detects the rotation angle of the corresponding servo motor 15. The robot main body 10 also has an amplifier unit 17 that applies a driving current to each servo motor 15.

[0017] 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 safety device 30. The robot control device 20 also outputs control signals to the amplifier unit 17 of the robot main body 10 and inputs detection signals from the encoder 16.

[0018] The control unit 21 of the robot control device 20 controls the operation of the robot main body 10 as follows. Specifically, the control unit 21 first sets a target angle for each joint axis of the articulated arm 12 using inverse kinematics based on the target position and target posture of the hand. Next, the control unit 21 acquires the current angle of each joint axis from the corresponding encoder 16 and sets a speed command value for each joint axis using feedback calculations (e.g., proportional-integral calculations or proportional-integral-derivative calculations) based on the difference between the target angle and the current angle. Next, the control unit 21 multiplies the speed command value by a speed limit value determined within a range from 0 (0%) to 1 (100%) to set a target speed that limits the speed command value. For example, if the speed limit value is 1 (100%), the target speed is the same as the speed command value. In other words, the robot speed is not limited. Furthermore, if the speed limit value is 0.5 (50%), the target speed is half the speed command value. Furthermore, if the speed limit value is 0 (0%), the target speed is 0 regardless of the speed command value. That is, the robot control device 20 stops the operation of the robot main 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 a 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 servo motor 15 outputs a torque corresponding to the set torque command.

[0019] In this embodiment, the robot safety device 30 is attached to the hand of the articulated arm 12. The safety device 30 detects an interfering object around the robot main body 10 and outputs a speed limit value according to the distance to the interfering object, etc. to the robot control device 20. In this embodiment, the safety device 30 also performs a self-diagnosis to determine whether or not a malfunction has occurred, and outputs a speed limit value according to the diagnosis result to the robot control device 20.

[0020] The safety device 30 includes a control unit 31 configured as a microprocessor including a CPU, ROM, and RAM, an I / O port 32 for exchanging signals with the control unit 21 of the robot control device 20, and a sensor unit 40 for monitoring the surroundings. Note that the signals exchanged between the control unit 31 of the safety device 30 and the control unit 21 of the robot control device 20 may be duplicated.

[0021] 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 transmission chirp, a receiving antenna 42 that receives a wave reflected from an object as a reception chirp, a synthesizer 43 that generates the transmission chirp, a mixer 44 that mixes the transmission chirp and the reception chirp to generate an intermediate frequency signal (IF signal), and a processing unit 45 that processes the IF signal to detect the distance L to the object, etc. The synthesizer 43 generates a transmission chirp signal modulated so that the frequency changes over time. In this embodiment, the synthesizer 43 generates a set (one frame) of N transmission chirps (N is a natural number greater than or equal to 2) spaced at regular intervals. The processing unit 45 includes an A / D converter 46 that performs A / D conversion on the IF signal generated by the mixer 44, a DSP 47 that performs Fourier transform processing (FFT processing) on ​​the A / D converted IF signal, etc. The DSP 47 performs FFT processing (distance FFT processing) on ​​the IF signal in chirp units to obtain a distance spectrum indicating the signal strength for each frequency. Since the frequency corresponds to the distance BIN, which is equivalent to the detection distance from the sensor unit 40, the distance L to the object can be calculated by determining the peak of the signal strength. Note that the DSP 47 may also perform FFT processing (velocity FFT processing) on ​​the data after the distance FFT processing in frame units to obtain a velocity spectrum. The relative velocity V to the object can be calculated by determining the peak of the signal strength in the velocity spectrum.

[0022] Here, peak detection is performed by determining whether the signal strength exceeds a peak detection threshold at any distance BIN (see FIG. 3A ). The peak detection threshold can be set, for example, using a constant false alarm rate (CFAR). However, if the overall signal strength weakens due to a malfunction of the safety device 30 (e.g., malfunction of the transmitting antenna 41 or the receiving antenna 42, malfunction of the power supply circuit, etc.), the signal strength may fall below the peak detection threshold at all distance BINs, even if an object is present around the safety device 30 (see FIG. 3B ). As a result, the safety device 30 may be unable to detect the object, and safety may not be ensured. Therefore, the safety device 30 of this embodiment performs self-diagnosis to determine whether a malfunction has occurred. If a malfunction is detected, the safety device 30 transmits a control signal (speed limit value) to the robot control device 20 to stop the operation of the robot main body 10.

[0023] Next, the operation of the safety device 30 of this embodiment will be described. In particular, the operation when the safety device 30 performs self-diagnosis of its own failure will be described. Fig. 4 is a flowchart showing an example of an object detection process executed by the control unit 31 (CPU) of the safety device 30. This process is repeatedly executed at predetermined time intervals (for example, every few msec or every tens of msec).

[0024] In the object detection process, the control unit 31 first acquires a distance spectrum indicating signal strength for each frequency (distance BIN) from the sensor unit 40 (S100). FIG. 5A shows an example of a distance spectrum acquired from the sensor unit 40. Next, the control unit 31 calculates, for each distance BIN, a differential intensity ΔA (=A-B), which is the difference between the acquired signal strength A and a preset comparison intensity B (S102). Here, in this embodiment, the comparison intensity B is the signal strength (dark noise) for each distance BIN measured by the sensor unit 40 in a space without a detected object. Therefore, the differential intensity ΔA is the signal strength obtained by removing the dark noise component from the signal strength A obtained by the sensor unit 40. FIG. 5B shows an example of the comparison intensity B for each distance BIN. FIG. 5C shows an example of the differential intensity ΔA for each distance BIN. Then, the control unit 31 extracts the differential intensity ΔAn in the close distance range from the differential intensity ΔA for each distance BIN (S104), and determines whether the differential intensity ΔAn is greater than or equal to a predetermined negative threshold value α for any of the extracted distance BINs in the close distance range (S106).

[0025] If the control unit 31 determines that the differential intensity ΔAn is equal to or greater than the negative threshold value α for any distance BIN in the short distance range, it determines that there is no abnormality in the robot itself, sets the number of abnormality detections N to 0 (S108), and performs the peak determination described above (S110). Next, the control unit 31 calculates the distance to the object based on the distance BIN corresponding to the peak differential intensity ΔA (S112), and sets a speed limit value for the robot main body 10 based on the distance to the object (S114). The speed limit value is set so that the shorter the distance to the object, the greater the speed limit value for the robot main body 10. In this embodiment, as described above, the speed limit value is set within a range of 0 to 1 as a ratio of the target speed to the speed command value for the robot main body 10. The control unit 31 then transmits the set speed limit value to the robot control device 20 (S116) and ends the object detection process.

[0026] If the control unit 31 determines in S106 that the differential intensity ΔAn is less than the negative threshold value α at any distance BIN in the short-distance range, it increments the abnormality detection count N by 1 (S118) and determines whether the abnormality detection count N is equal to or greater than a predetermined count Nref (S120). Here, the predetermined count Nref is the number of abnormality detections required to confirm the diagnosis of a malfunction of the safety device itself, and is predetermined, e.g., 5 or 10 times. The threshold value α and the predetermined count Nref may be set based on the results of statistically calculating the variation in signal strength in the short-distance range measured by multiple safety devices 30. If the control unit 31 determines that the abnormality detection count N is less than the predetermined count Nref, it proceeds to S110 and executes the processes of S110 to S116. On the other hand, if the control unit 31 determines that the abnormality detection count N is equal to or greater than the predetermined count Nref, it determines that a malfunction has occurred in the control unit 31 (S122). The control unit 31 then sets the speed limit value to 0 (S124), transmits the speed limit value to the robot control device 20 (S116), and terminates the object detection process. The robot control device 20 sets the target speed by multiplying the speed command value by the speed limit value. Therefore, when the robot control device 20 receives a speed limit value of 0, it sets the target speed to 0 regardless of the speed command value. This causes the robot control device 20 to stop the operation of the robot main body 10. Therefore, even if a failure occurs in the safety device 30 and it becomes unable to detect nearby interfering objects, the safety of the surrounding area can be ensured. If the difference intensity ΔAn is determined to be equal to or greater than the negative threshold value α before the abnormality detection count N becomes equal to or greater than the predetermined number Nref, the abnormality detection count N is reset to 0 in S108. Therefore, the control unit 31 determines that a failure has occurred in itself when the number of consecutive times that the difference intensity ΔAn is determined to be less than the negative threshold value α becomes equal to or greater than the predetermined number Nref (when this continues for a time equal to or greater than the execution time interval of the object detection process multiplied by the predetermined number Nref).

[0027] FIG. 6 is an explanatory diagram showing an example of the differential intensity of each distance BIN during a malfunction. Because the comparison intensity B is a fixed value, if the signal intensity A weakens overall due to a malfunction of the sensor unit 40 or the like, the differential intensity ΔA will appear as a negative value except for the distance BIN band where an object is present (see FIG. 6 ). Therefore, the control unit 31 can self-diagnose the presence or absence of a malfunction by determining whether the differential intensity ΔA is less than the negative threshold α for any distance BIN. However, if an object is present at a very short distance from the sensor unit 40, most of the reflected waves received by the sensor unit 40 will be reflected from the object, and fewer will be reflected from distances behind the object. Therefore, even if no malfunction has occurred, the differential intensity ΔA will be negative in areas other than the short distance range (see FIG. 7 ). In this case, performing self-diagnosis based on whether the differential intensity ΔA in areas other than the short distance range is less than the negative threshold α may result in an erroneous malfunction diagnosis. In this embodiment, the differential intensity ΔA used for self-diagnosis is limited to the differential intensity ΔAn in the short distance range, so that even if an object is present at an extremely short distance from the sensor unit 40, it is possible to prevent a false diagnosis of a malfunction.

[0028] Here, the correspondence between the main elements of the embodiment and the main elements of the present disclosure described in the claims will be described. That is, the safety device 30 of the present embodiment corresponds to the object detection device of the present disclosure, the sensor unit 40 is an example of a sensor unit, the control unit 31 that executes the processing of S100-S112 of the object detection processing is an example of a determination unit, and the control unit 31 that executes the processing of S118-S122 of the object detection processing is an example of a diagnosis unit. Also, the robot main body 10 is an example of a robot, and the robot control device 20 is an example of a robot control device.

[0029] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure.

[0030] For example, in the above-described embodiment, the negative threshold value α and the predetermined number of times Nref are determined in advance, but they may also be set by an operator's operation.

[0031] In the above-described embodiment, the control unit 31 diagnoses its own malfunction based on whether the differential intensity ΔAn is less than the negative threshold value α for any distance BIN in the short distance range. However, the control unit 31 may also diagnose its own malfunction based on whether the differential intensity ΔAn is less than the negative threshold value α for all distance BINs in the short distance range. Furthermore, the control unit 31 may also diagnose its own malfunction based on whether the differential intensity ΔAn is less than the negative threshold value α for a predetermined number or more of distance BINs in the short distance range.

[0032] In the above-described embodiment, the control unit 31 diagnoses itself as having a malfunction when the state in which the differential intensity ΔAn is less than the negative threshold value α is determined a predetermined number of times Nref or more consecutively. However, the control unit 31 may also diagnose itself as having a malfunction when the state in which the differential intensity ΔAn is less than the negative threshold value α is determined a predetermined number of times Nref or more within a predetermined time. In this case, the object detection process of the modified example shown in FIG. 8 can be executed instead of the process shown in FIG. 4. Note that the same steps as those in FIG. 4 are assigned the same step numbers, and their descriptions will be omitted to avoid duplication.

[0033] In the object detection process of the modified example, if the control unit 31 determines in S106 that the differential intensity ΔAn in the short distance range is less than the negative threshold value α, it determines whether the timer T has a value of 0 (S200). If the control unit 31 determines that the timer T has a value of 0, it starts the timer T (S202) and proceeds to S204. If the control unit 31 determines that the timer T has not a value of 0, i.e., that the timer T has already started, it proceeds to S204. Next, the control unit 31 determines whether the value of the timer T is less than a predetermined value Tref (S204). If the control unit 31 determines that the value of the timer T is less than the predetermined value Tref, it increments the abnormality detection count N by 1 (S118). If the control unit 31 determines that the abnormality detection count N is equal to or greater than the predetermined count Nref (YES in S120), it determines that a malfunction has occurred in the control unit 31 (S122). On the other hand, if the value of the timer T becomes equal to or greater than the predetermined value Tref in S204 before the number of abnormality detections N becomes equal to or greater than the predetermined number Nref, the control unit 31 determines that the time has expired, resets the value of the timer T and the value of the number of abnormality detections N to 0 (S206), and proceeds to S110. Thus, in the object detection process of the modified example, the control unit 31 diagnoses itself as having a malfunction if the number of abnormality detections N (the number of times a state in which the differential intensity ΔAn is less than the negative threshold value α is detected) becomes equal to or greater than the predetermined number Nref before the value of the timer T becomes equal to or greater than the predetermined value Tref (before the time expires).

[0034] In the embodiment described above, the control unit 31 performs self-diagnosis of a malfunction based on whether or not the differential intensity ΔAn in the short-distance range is less than the negative threshold value α. However, depending on the application of the safety device 30, the control unit 31 may also perform self-diagnosis of a malfunction based on whether or not the differential intensity ΔA is less than the negative threshold value α in areas other than the short-distance range.

[0035] In the above-described embodiment, the safety device 30 sets the speed limit value based on the distance L to the object, but the speed limit value may also be set based on a combination of the distance L to the object and the relative speed (approach speed to the object) V. In this case, the control unit 31 may set the speed limit value so that the shorter the distance L to the object and the faster the relative speed V, the greater the speed limit of the robot main body 10. Furthermore, the control unit 31 may calculate an expected arrival time until the robot main body 10 reaches the sensor unit 40 based on the combination of the distance L to the object and the relative speed V, and set the speed limit value based on the expected arrival time.

[0036] In the above-described embodiment, the control unit 31 of the safety device 30 sets a speed limit value based on the distance L to the object and transmits the speed limit value to the robot control device 20. However, the control unit 31 of the safety device 30 may transmit the distance L to the object to the robot control device 20, so that the robot control device 20 sets a speed limit value based on the distance L.

[0037] In the above-described embodiment, the safety device 30 is attached to the hand (tip) of the articulated arm 12 of the robot main body 10. However, the safety device 30 may also be attached to the base 11 of the robot main body 10. Furthermore, while the safety device 30 is provided on a stationary robot, it may also be provided on a self-propelled robot. The self-propelled robot may be an arm robot with the above-described articulated arm, or a transport robot. For example, as shown in FIG. 9 , the self-propelled robot may be an automatic exchange robot 110 that moves along the mounting line 100 to exchange the feeders 102 for each of the component mounters 101 in a mounting line 100 having feeder tables arranged in the transport direction of the board and each of which has a detachable feeder 102. When an interfering object is detected within the detection range, the safety device 30 outputs a speed limit value corresponding to the relative distance L from the interfering object to the automatic exchange robot 110. The automatic exchange robot 110 multiplies the input speed limit value by the speed command value, and travels at a travel speed limited according to the speed limit value. Furthermore, when the safety device 30 diagnoses that a failure has occurred, it outputs a speed limit value of 0 to the automatic exchange robot 110, causing the automatic exchange robot 110 to stop traveling.

[0038] As described above, the object detection device of the present disclosure calculates, for each distance, a differential intensity, which is the difference between the intensity for each distance acquired based on the output signal from the sensor unit and a predetermined comparison intensity, and detects the peak of the differential intensity for each distance to determine the presence or absence of an object. For example, by measuring background noise in advance and setting the measured intensity as the comparison intensity, the influence of the background noise on the intensity can be eliminated, allowing for accurate object detection. Furthermore, while the intensity acquired based on the output signal from the sensor unit decreases due to a sensor failure, the comparison intensity remains constant, so the differential intensity appears with an inverted sign due to a sensor failure. Therefore, by comparing the differential intensity with a threshold value of an inverted sign, the object detection device can more reliably self-diagnose a failure with a simple process.

[0039] In the object detection device according to the present disclosure, the diagnosing unit may diagnose a fault in the object detection device when the differential intensity exceeds the threshold in the direction of the opposite sign. By determining whether the differential intensity exceeds the threshold in the direction of the opposite sign, a fault in the object detection device can be more reliably diagnosed through simple processing.

[0040] In this case, the diagnosing unit may diagnose that the object detection device has a malfunction when the differential intensity in the short distance range, among the differential intensity for each distance, exceeds the threshold in the direction of the opposite sign. This makes it possible to prevent erroneous diagnosis of a malfunction even when an object is present at an extremely short distance from the sensor unit. In these cases, the diagnosing unit may diagnose that the object detection device has a malfunction when the differential intensity continues to exceed the threshold in the direction of the opposite sign for a predetermined period of time, or the diagnosing unit may diagnose that the object detection device has a malfunction when the differential intensity exceeds the threshold in the direction of the opposite sign a predetermined number of times or more within a predetermined period of time. This makes it possible to prevent erroneous diagnosis of a malfunction due to noise.

[0041] In addition, the present disclosure may be embodied in a robot system instead of an object detection device. In the robot system, if a fault in the object detection device is diagnosed, the robot's operation is stopped to ensure safety. The present disclosure may also be embodied in a fault diagnosis method.

[0042] The present disclosure is applicable to industries such as the manufacturing of safety devices and robot systems.

[0043] 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 Safety device, 31 Control unit, 32 I / O port, 40 Sensor unit, 41 Transmitting antenna, 42 Receiving antenna, 43 Synthesizer, 44 Mixer, 45 Processing unit, 46 ADC, 47 DSP, 100 Mounting line, 101 Component mounter, 102 Feeder, 110 Automatic exchange robot.

Claims

1. An object detection device that detects objects, comprising: a sensor unit that transmits and receives electromagnetic waves; a judgment unit that acquires intensity for each distance based on an output signal from the sensor unit, calculates a differential intensity for each distance, which is the difference between the acquired intensity and a predetermined comparison intensity, and determines the presence or absence of the object by detecting a peak of the differential intensity with respect to the distance; and a diagnosis unit that diagnoses a malfunction of the object detection device by comparing the differential intensity with a threshold value of the opposite sign.

2. An object detection device according to claim 1, wherein the diagnosing unit diagnoses that a fault has occurred in the object detection device when the differential intensity exceeds the threshold value in the direction of the opposite sign.

3. An object detection device as described in claim 2, wherein the diagnosis unit diagnoses that a malfunction has occurred in the object detection device when the differential intensity in the short distance range, among the differential intensity for each distance, exceeds the threshold in the direction of the opposite sign.

4. An object detection device as described in claim 2 or 3, wherein the diagnosis unit diagnoses that a malfunction has occurred in the object detection device when the state in which the differential intensity exceeds the threshold value in the direction of the opposite sign continues for a predetermined period of time.

5. An object detection device as claimed in claim 2 or 3, wherein the diagnosis unit diagnoses that a malfunction has occurred in the object detection device if a state in which the differential intensity exceeds the threshold value in the direction of the opposite sign occurs a predetermined number of times or more within a predetermined period of time.

6. A robot system comprising: a robot; an object detection device provided on the robot, the object detection device having a sensor unit that transmits and receives electromagnetic waves, a determination unit that acquires intensity for each distance based on an output signal from the sensor unit, calculates a differential intensity for each distance which is the difference between the acquired intensity and a predetermined comparison intensity, and determines the presence or absence of the object by detecting a peak of the differential intensity with respect to the distance, and a diagnosis unit that diagnoses a malfunction of the object detection device by comparing the differential intensity with a threshold value of an opposite sign; and a robot control device that stops the operation of the robot when a malfunction of the object detection device is diagnosed by the diagnosis unit while the robot is operating.

7. A fault diagnosis method for diagnosing a fault in an object detection device comprising a sensor unit which transmits and receives electromagnetic waves, and a judgment unit which acquires intensity for each distance based on an output signal from the sensor unit, calculates a differential intensity for each distance which is the difference between the acquired intensity and a predetermined comparison intensity, and judges the presence or absence of an object by detecting a peak of the differential intensity with respect to the distance, the fault diagnosis method comprising: comparing the differential intensity with a threshold value of an opposite sign; and diagnosing that a fault has occurred in the object detection device if the differential intensity exceeds the threshold value in the direction of the opposite sign.

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