JP5278389B2 - Cable breakage detection device and cable breakage detection method - Google Patents

Description

  The present invention relates to a disconnection detection apparatus and method capable of detecting a disconnection of an electric wire / cable.

With an encoder cable that is connected by serial communication between the servo controller that controls the servo motor provided in the robot mechanism and the encoder device that detects the position or posture of the servo motor, the encoder cable may be bent due to the movement of the robot. Because it is constantly stressed, disconnection may occur due to long-term operation. If a disconnection occurs, the robot system cannot operate normally. In order to recover from an abnormal state due to this signal line disconnection, it is necessary to identify the disconnection location and replace the disconnected encoder cable, resulting in a long stoppage of the production equipment and a decrease in productivity.
In addition, similar disconnection of the cable occurs even when the control device and the operating device are connected to each other by communication, due to dragging of the cable accompanying movement of the operating device, pinching by the device, or the like.

As a general method for detecting conductor breakage in electric wires / cables, there is a method in which a DC current for wire breakage detection is passed through the conductors of wires / cables and the resistance value is measured, but a DC current or signal is applied for wire breakage detection. Therefore, it was impossible to detect when the robot was in operation, and it was necessary to stop the production equipment.
In addition, even if the wire is disconnected at the bent part, there is a case where an instantaneous disconnection phenomenon that returns to the contact state may occur when the bending is restored. was there.
To solve such problems, the communication transmission system is a differential signal that sends an electrical signal with a voltage difference between the two signals, and the line receiver excludes the two differential signals whose phases are reversed. There has been proposed a technique for detecting disconnection by logical OR (see, for example, Patent Document 1).

JP 2006-170657 A (FIG. 1)

However, the technique described in Patent Document 1 requires two line receivers, and therefore, the impedance of the transmission line becomes mismatched. Therefore, because of the obstruction factor that the reflection of the transmission line has a great influence, the technique is faster. There was a problem that it was difficult to apply to the communication.
The present invention has been made in view of such problems, and is a disconnection detection device capable of reliably detecting conductor disconnection of electric wires and cables with high-speed communication and even when the system is in operation. And its detection method.

  In order to solve the above-described problem, according to one aspect of the present invention, there is a difference between a first device including a first transceiver circuit and a second device including a second transceiver circuit. In a cable disconnection detection device of a communication device that is connected by a signal and performs communication based on control of a transmission / reception control circuit, the difference based on a frequency spectrum value in a preamble period of a common mode signal via a resistor between the differential signals. A cable disconnection detection device including a disconnection detection circuit that detects disconnection of a motion signal is applied.

  According to the present invention, by detecting the frequency spectrum of the common mode signal in the preamble period of the communication frame between the first device and the second device and comparing the frequency spectrum with a threshold value, it is possible to detect the disconnection of the electric wire / cable. As a result, it is possible to reliably detect the conductor breakage of the electric wire / cable while the system is operating (communication) with high-speed communication.

The block diagram of the cable disconnection detection apparatus of the communication circuit which concerns on 1st Embodiment of this invention. Differential signal and common mode signal waveforms before and after disconnection Normal mode common mode signal spectrum Spectrum of common mode signal at disconnection The block diagram of the disconnection detection circuit which concerns on 1st Embodiment of this invention. 1 is a block diagram of a transmission / reception control circuit according to a first embodiment of the present invention. 1 is a block diagram of a frame generation circuit according to a first embodiment of the present invention. Timing of sampling delay signal according to first embodiment of the present invention Operation flow chart of disconnection detection according to the first embodiment of the present invention. The block diagram of the disconnection detection circuit of the cable disconnection detection apparatus which concerns on 3rd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
First, the configuration of the cable breakage detection apparatus according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram of a cable break detection device for a communication circuit according to a first embodiment of the present invention. In the figure, communication is performed between a first device (not shown) and a second device (not shown), and the first transceiver circuit 1 and the second device of the first device (not shown). These devices (not shown) and the second transceiver circuit 2 are connected by a twisted pair cable by serial communication using differential signals 1a and 1b. Communication control is performed by a transmission / reception control circuit 4 that controls transmission / reception of the first transceiver circuit 1 and a reception control circuit 5 of the second transceiver circuit 2. The transmission / reception control circuit 4 and the transmission / reception control circuit 5 have the same configuration.
The serial communication is a Manchester code system, and the transmission speed is, for example, 4 Mbps (bit / per / second). As a general communication synchronization method, the transmitting side transmits a bit string in which a plurality of “0” s and “1” s called preambles are alternately arranged at the beginning of a frame at the time of data transmission. For this reason, the preamble in the 4 Mbps Manchester code system is a half 2 MHz bit string. The preamble is a signal used for communication timing synchronization between two systems in communication.

Resistors 11 and 12 are differential mode termination resistors on the first transceiver circuit 1 side, and resistors 21 and 22 are differential mode termination resistors on the second transceiver circuit 2 side and have the same resistance value.
The resistor 13 is a common mode termination resistor on the first transceiver circuit 1 side, and the resistor 23 is a common mode termination resistor on the second transceiver circuit 2 side and has the same resistance value. Each termination resistor 13, 23 is connected to a shield ground FG of the cable via a capacitor.
Reference numeral 3 denotes a disconnection detection circuit. When a disconnection of the differential signal 1a or 1b is detected, a disconnection detection signal 6a is output.
The first transceiver circuit 1, the transmission / reception control circuit 4 and the disconnection detection circuit 3 are provided in the first device, and the second transceiver circuit 2 and the transmission / reception control circuit 5 are provided in the second device.

The principle of detecting a disconnection of a differential signal will be described below.
2A and 2B show examples of differential signal and common mode signal waveforms. FIG. 2A shows a waveform at the time of normal (non-disconnection), and FIG. 2B shows a waveform at the occurrence of disconnection of the differential signal 1a. 13a is a common mode signal, which is a combined signal of differential signals 1a and 1b having different phases. In the case of an ideal system, the differential signals 1a and 1b cancel each other, and only the offset constant voltage component is observed in the common mode signal 13a. However, as shown in FIG. 2A, due to variations in the rise and fall of the transceiver output, the common mode signal 13a protrudes when the transceiver output changes from H level to L level or from L level to H level. Signal is observed.
Further, FIG. 2B shows a case where the line disconnection of the differential signal 1a occurs. The differential signal 1a is a predetermined voltage during normal operation due to the induced voltage of the differential signal 1b on the non-disconnected side. However, the voltage is low and the signal waveform is in phase with the differential signal 1b. The balance of the differential signal path is lost due to the impedance of the disconnection portion and the coupling capacitance between the differential signal paths, and the balance is converted to the normal mode. As a result, the common mode signal 13a shown in FIG. It becomes.

FIG. 3 shows the frequency spectrum of the common mode signal 13a during the preamble period when the differential signal 1a is normal (not disconnected). It has a spectrum peak at a fundamental frequency of 2 MHz of the preamble and harmonics 4 MHz, 6 MHz, and 8 MHz of its integral multiple components.
FIG. 4 is a frequency spectrum of the common mode signal 13a during the preamble period when the line of the differential signal 1a is disconnected. At the preamble fundamental frequency of 2 MHz and its odd harmonic components of 6 MHz and 10 MHz, the peak of the spectrum is more than twice that of the normal case. This is because the common mode signal 13a becomes a rectangular wave because the differential signal is not canceled due to the disconnection, and the odd harmonic component of the fundamental frequency rises.

Next, the configuration and operation of the disconnection detection device 3 that implements the present invention will be described.
FIG. 5 is a block diagram of the disconnection detection circuit 3.
In FIG. 5, the disconnection detection circuit 3 includes a low-pass filter 31, an AD converter 32, a DFT calculator 33, and a determiner 6, and performs an FFT operation on the common mode signal in the preamble period to detect disconnection from the frequency spectrum value. To do.

FFT is Fast Fourier Transform, which is a method for converting a time-series signal to a frequency spectrum value on the frequency axis (generating a frequency spectrum value).
The FFT is intended for a continuous function. The discrete digital data sampled by the AD converter 32 is subjected to a discrete Fourier transform called DFT (Discrete Fourier Transform) by the DFT calculator 33, thereby converting the time series signal. Convert to frequency spectrum value of frequency axis. At this time, the low pass filter 31 is used before sampling in order to prevent a phenomenon called aliasing in which a high frequency component that does not exist in the source signal appears. In the present embodiment, the frequency for DFT calculation is set to a frequency 20 MHz which is ten times sufficient for spectrum detection of the main component of the preamble, and this is set as the cutoff frequency of the low-pass filter 31. The sampling frequency of the AD converter 32 is 40 MHz, which is twice the cut-off frequency.

  Reference numeral 4a denotes a sampling delay signal (details will be described later) output from the transmission / reception control circuit 4, which is connected to the enable terminal of the AD converter 32 and normally stops at the L level. The sampling delay signal 4a is delayed for a predetermined time during transmission of the preamble and becomes H level (active). During this time, the AD converter 32 performs processing. The digital data output from the AD converter 32 is input to the DFT calculator 33, which converts the digital data into a frequency spectrum and outputs the spectrum values of 2 MHz, 6 MHz, and 10 MHz to the determiner 6.

The determination unit 6 includes determination registers 61, 62, and 63 that can be arbitrarily set, comparators 64, 65, and 66, and an AND circuit 67 which is a logical product circuit. The determination registers 61, 62, and 63 are threshold values of spectrum values of 2 MHz, 6 MHz, and 10 MHz, respectively. For example, a spectrum value that is twice that of normal time (before disconnection) is obtained in advance from a control unit (not shown) of the first device. Is set. The spectrum value of each frequency is compared with each threshold value by the comparators 64, 65, and 66, and a peak rise is determined. When the outputs of all the comparators 64, 65, 66 exceed the threshold value, the AND circuit 67 determines that the cable is disconnected, and outputs the disconnection detection signal 6a at the H level.
By determining with all the comparison values, it is possible to determine the fundamental frequency peculiar to the rectangular wave and the rise of the harmonic spectrum of the odd component.
In the present embodiment, the outputs of all three comparators are input to the AND circuit. As is clear from comparison between FIG. 3 and FIG. 4, the cable is based on the outputs of one or two comparators. Although it is possible to determine the disconnection, considering the distinction from the influence due to noise or the like, it is desirable to determine the cable disconnection based on the outputs of at least two comparators.
When the disconnection detection signal 6a is output at the H level, it is held by a latch circuit (not shown) and read by the control unit (not shown) of the first device to shut off the servo power, display it, and output an abnormal signal. , Perform other abnormal processing.

Next, a generation circuit of the sampling delay signal 4a for detecting the disconnection will be described.
FIG. 6 is a block diagram of the transmission / reception control circuit 4. The transmission / reception control circuit 4 includes a CPU interface circuit 41 connected to a transmission control circuit 9, a reception control circuit 10, and a CPU interface 4c provided in a control unit (not shown) of the first device. The CPU sets transmission data and determination registers 61, 62, and 63 via the CPU interface circuit 41. A transmission data memory 42 stores transmission data, and a CRC generation circuit 44 generates redundant data from the transmission data for error detection called CRCC (Cyclic Redundancy Check Code). A frame generation circuit 7 generates a transmission frame 7a from the transmission data 42a and the CRC data 44a. When the frame is generated, the transmission circuit 45 converts the frame into a Manchester code signal 4 b and outputs the Manchester code signal 4 b to the first transceiver circuit 1. Reference numeral 7b denotes a sampling signal which is at the H level only during the preamble period.
A delay circuit 8 generates a sampling delay signal 4a obtained by delaying the sampling signal 7b by the filter time constant of the low-pass filter 31, and delays the processing of the AD converter 31.

Next, a generation circuit for the sampling signal 7b will be described with reference to FIG.
In FIG. 7, 75 is a register for storing the preamble data of the transmission frame, 74 is a register for storing the start flag of the transmission frame, and 73 is a register for storing the transmission data 42a of the transmission frame transferred from the transmission data memory 42. 72 is a register for storing CRC data 44a of the transmission frame generated by the CRC generation circuit 44, and 71 is a register for storing an end flag of the transmission frame. Reference numeral 77 denotes a state machine that controls the selector 76 to form a transmission frame in the order of preamble data, start flag, transmission data, CRCC, and end flag. The data selected by the selector 76 is converted from parallel data to serial data 7a by a parallel-serial converter 78.

Next, the timing of the sampling delay signal 4a will be described with reference to FIG.
In FIG. 8, the position request frame transmitted from the first device to the second device (for example, the encoder device) includes a preamble, a start flag (SF), transmission data, CRCC, and an end flag (EF). . The sampling signal 7b becomes H level during the preamble period. The sampling delay signal 4 a is a signal obtained by delaying the sampling signal 7 b by the filter time constant of the low-pass filter 31.

Next, an operation flow of disconnection detection showing the operation of the present embodiment will be described with reference to FIG. First, a threshold value of a spectrum value for disconnection is set in the determination registers 61, 62, and 63 (threshold setting step).
During the preamble period, the sampling delay signal 4a becomes H level (preamble period determining step), the frequency spectrum value of the common mode signal is measured (spectrum generation step), and compared with the threshold value by the comparators 64, 65, 66 (comparison step). ). When the threshold value is exceeded, the disconnection detection signal 6a becomes H level (disconnection detection signal determination step), the disconnection is notified, and abnormality processing (abnormal processing step) is executed.

Second Embodiment
The cable break detection device according to the first embodiment of the present invention has been described above. Next, the disconnection detection circuit of the cable disconnection detection apparatus according to the second embodiment of the present invention will be described with reference to FIG. FIG. 10 is a block diagram of the disconnection detection circuit of the cable disconnection detection apparatus according to the second embodiment of the present invention. A band-pass filter is used instead of the DFT operation of the disconnection detection circuit 3 shown in the first embodiment. And similar results can be obtained.
In the figure, the disconnection detection circuit 50 includes bandpass filters 51, 52, 53, rectifiers 54, 55, 56, AD converters 57, 58, 59, and a determination device 6 similar to the disconnection detection device 3. The

  The common mode signal 13a passes through the frequency components of the fundamental frequency 2 MHz and the odd harmonic components 6 MHz and 10 MHz by the band-pass filters 51, 52 and 53, respectively. The passed signals are rectified and smoothed by the rectifiers 54, 55 and 56, respectively, and output to the AD converters 57, 58 and 59, respectively. When the sampling delay signal 4a described in the first embodiment is connected to the enable terminals of the AD converters 57, 58, and 59, respectively, and normally stops at the L level and becomes the H level (active), the AD converters 57, 58, 59 starts the process. The digital data output from the AD converters 57, 58 and 59 is output to the determination unit 6 similar to the disconnection detection device 3, and when the peak rise at the time of disconnection is determined, the disconnection detection signal 6a becomes H level. Thus, the same result as in the first embodiment can be obtained, and a disconnection can be detected.

Actually, in the case of 4 Mbps, which is an example of the transmission rate in the first embodiment, the value of the quality factor (sharpness) Q representing the attenuation characteristics of the filters of the bandpass filters 51, 52, 53 is calculated from the adjacent frequency. Considering the influence of the above, disconnection could be detected by setting it to about 10.
In the first embodiment and the second embodiment, serial communication has been described as a Manchester code method. However, the present invention detects disconnection based on a preamble period signal for synchronizing transmission and reception timings. Therefore, the present invention is not limited to the Manchester encoding method, and can be applied to other communication methods that synchronize the transmission / reception timing with the preamble.

  Since this structure is used, a disconnection is detected during the preamble period of transmission from the first device while communication is always performed between the first device and the second device. Further, no circuit for detecting disconnection is added to the communication path, impedance matching between them is not lost, and the present invention can also be applied to cases where the communication speed of this embodiment is exceeded. A robot, a numerical control device, and other production facilities use a motor for power, and can be applied to serial communication between an encoder provided in the motor and a control device that drives and controls the motor.

1: first transceiver circuit 1a, 1b: differential signal 2: second transceiver circuit 3, 50: disconnection detection circuit 4: transmission / reception control circuit 4a: sampling delay signal 4b: Manchester code signal 4c: CPU interface 5: transmission / reception Control circuit 6: Determinator 6a: Disconnection detection signal 7: Frame generation circuit 7a: Transmission frame 7b: Sampling signal 8: Delay circuit 9: Transmission control circuit 10: Reception control circuits 11, 12, 21, 22: Termination of differential mode Resistors 13 and 23: Common mode termination resistor 13a: Common mode signal 31: Low-pass filter 32, 57, 58, 59: AD converter 33: DFT calculator 41: CPU interface circuit 41a: Delay data 42: Transmission data memory 42a : Transmission data 44: CRC generation circuit 44a: CRC Data 51, 52, 53: Band pass filters 54, 55, 56: Rectifiers 61, 62, 63: Determination registers 64, 65, 66: Comparator 67: AND circuit 71: End flag storage register 72: CRC data storage Register 73: Transmission data storage register 74: Start flag storage register 75: Preamble data storage register 76: Selector 77: State machine

Claims (8)

The first device including the first transceiver circuit and the second device including the second transceiver circuit are connected to each other by a differential signal, and the first device and the second device A cable disconnection detection device for a communication circuit that performs communication based on control of a transmission / reception control circuit included in each,
A cable disconnection detection device comprising: a disconnection detection circuit that detects disconnection of the differential signal based on a frequency spectrum value in a preamble period of a common mode signal via a resistor between the differential signals. The disconnection detection circuit includes:
A low pass filter for cutting high frequency components of the common mode signal;
An AD converter that converts a sampling delay signal obtained by delaying an output of the low-pass filter by a predetermined time from a preamble period of the communication into digital data only during an active period;
A DFT calculator for calculating a frequency spectrum value by performing a discrete Fourier transform on the digital data;
A determinator that determines that the cable is disconnected when the frequency spectrum value exceeds a predetermined frequency spectrum threshold;
The cable disconnection detection device according to claim 1, comprising: The determiner is
Multiple decision registers that can be set arbitrarily,
Multiple comparators;
An AND circuit,
The plurality of determination registers include a frequency spectrum threshold corresponding to a spectrum of a fundamental frequency of the common mode signal, a frequency spectrum threshold corresponding to a harmonic spectrum of a triple component of the fundamental frequency, and five times the fundamental frequency. Store the frequency spectrum threshold corresponding to the harmonic spectrum of the component,
The plurality of comparators respectively compare the frequency spectrum values calculated by the DFT calculator and the frequency spectrum threshold values stored in the plurality of determination registers,
3. The cable disconnection detection apparatus according to claim 2, wherein a logical product of the results of at least two of the comparators is obtained by the AND circuit and used as a disconnection detection signal. The disconnection detection circuit includes:
A plurality of bandpass filters through which a fundamental frequency of the common mode signal, a third harmonic component and a fifth harmonic component pass;
A plurality of rectifiers for rectifying and smoothing each of the outputs of the plurality of bandpass filters;
A plurality of AD converters that convert the sampling delay signal obtained by delaying the outputs of the plurality of rectifier units by a predetermined time from the communication preamble period into digital data only during an active period and output the frequency spectrum value;
A determinator that determines that the cable is disconnected when the frequency spectrum value exceeds a predetermined frequency spectrum threshold;
The cable disconnection detection device according to claim 1, comprising: The determiner is
Multiple decision registers that can be set arbitrarily,
Multiple comparators;
An AND circuit,
The plurality of determination registers include a frequency spectrum threshold corresponding to a spectrum of a fundamental frequency of the common mode signal, a frequency spectrum threshold corresponding to a harmonic spectrum of a triple component of the fundamental frequency, and five times the fundamental frequency. Store the frequency spectrum threshold corresponding to the harmonic spectrum of the component,
The plurality of comparators compare the frequency spectrum values output from the plurality of AD converters with the frequency spectrum threshold values stored in the plurality of determination registers, respectively.
5. The cable disconnection detection apparatus according to claim 4, wherein a logical product of the results of at least two of the comparators is obtained by the AND circuit and used as a disconnection detection signal.   5. The cable disconnection according to claim 2, wherein the sampling delay signal is a signal that delays a signal during a period in which a preamble of the communication frame is transmitted by a time constant of the low-pass filter. Detection device. The first device having the first transceiver circuit and the second device having the second transceiver circuit are connected to each other by a differential signal transmitted in the cable, and based on the control of the transmission / reception control circuit A cable disconnection detection method in a communication device for performing communication,
A cable breakage detection method comprising a breakage detection step of detecting a breakage of the differential signal based on a frequency spectrum value in a preamble period of a common mode signal via a resistor between the differential signals. The disconnection detecting step
A threshold setting step for setting a threshold of a frequency spectrum value at the time of cable disconnection;
A preamble period determination step of determining whether the preamble period is based on a sampling delay signal;
A spectrum generating step for obtaining a frequency spectrum value of the preamble period;
A comparison step of comparing the threshold value with the frequency spectrum value obtained in the spectrum generation step;
A disconnection detection signal determination step for determining whether or not the disconnection is based on the disconnection detection signal output in the comparison step;
A step of shifting to an abnormality processing step for executing an abnormality process when it is determined that the disconnection is detected in the disconnection detection signal determination step;
The cable disconnection detection method according to claim 7, further comprising:

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