Control device and control method applied to millimeter wave nondestructive testing imaging system

Abstract

The invention discloses a device applied to a millimeter wave nondestructive testing imaging system, which is dominated by a Linux application program running on a ZYNQ ARM core and can realize high-resolution near-field millimeter wave radar imaging. Firstly, a system is powered on, modules such as a radar and a guide rail are reset through a ZYNQ board card, then the radar is started through the ZYNQ board card, the radar is configured to be in an external trigger mode, working parameters are configured, a radar data receiving script is pulled up at the PS end of the ZYNQ board card, an external trigger source is provided for the radar from the PL end of the ZYNQ board card, meanwhile, reset of the guide rail is canceled, and the guide rail starts to work. And finally, after the guide rail program finishes running, radar data receiving is stopped, and the radar is reset. According to the invention, based on a radar external trigger mode and the guide rail controller, stable synchronous control of radar acquisition and guide rail operation of the millimeter wave nondestructive testing system is realized, the limitation that guide rail movement and radar acquisition of a traditional radar acquisition system cannot be synchronously started is solved, and the difficulty of data post-processing track calibration is greatly simplified; and the imaging processing time is greatly shortened.

Description

Technical Field

[0001] The present invention belongs to the technical field of millimeter wave radar imaging and nondestructive testing, and in particular relates to a control framework applied to a millimeter wave nondestructive testing imaging system. Background Art

[0002] Non-destructive testing refers to a method of inspecting and testing the internal and surface structure, state, and type, quantity, shape, nature, location, size, distribution, and changes of defects of a test piece by using physical or chemical methods, with the help of modern technology and equipment, without damaging or affecting the performance of the tested object or the internal structure of the tested object. Non-destructive testing is an indispensable and effective tool for industrial development and, to a certain extent, reflects the level of industrial development of a country.

[0003] Unlike traditional nondestructive testing methods, this system implements nondestructive testing based on millimeter-wave synthetic aperture radar technology. Synthetic aperture radar (SAR) is an advanced technology that uses radar technology and signal processing to achieve high-resolution microwave imaging. It simulates the effect of a large antenna aperture, transmits and receives signals from a mobile platform, and generates high-definition target images through complex phase adjustment and synthesis processing. Millimeter-wave radar operates at a frequency of 30GHz to 300GHz, has good perspective effects, and combines multiple advantages such as low cost, small size, and no ionizing radiation. Synthetic aperture radar technology based on millimeter-wave radar can image near-field materials, workpieces, etc., achieving low-energy, low-cost, high-efficiency, and high-precision nondestructive testing.

[0004] However, conventional millimeter-wave synthetic aperture radar (SAR) imaging systems have a small imaging area and require high imaging precision. Traditional imaging experiments typically involve manually synchronizing radar power-up with rail operation, or starting the radar first and then operating the rail. These methods result in unstable radar data frame header positions, requiring manual searching for every possible starting frame position. This significantly impacts the consistency and timeliness of subsequent data processing and reduces the quality of the final imaging results. Therefore, developing a system framework that effectively controls the synchronous acquisition and operation of the radar and rail is a key issue. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a control device for a nondestructive testing imaging system that can achieve stable millimeter-wave nondestructive testing system radar acquisition and synchronous control of guide rail operation, and provides a control method for performing nondestructive testing by the control device.

[0006] The object of the present invention is achieved through the following technical solutions: A control device for a millimeter wave nondestructive testing imaging system, comprising a signal processing module, a radar radio frequency module, a guide rail controller, and a host computer instruction module respectively connected to the signal processing module; the guide rail controller is connected to the stepping motor guide rail module, and the radar radio frequency module is used to transmit and receive radar echo signals;

[0007] The signal processing module uses the XCZU9EG-2FFVG1956I chip, and the radar RF module uses SiRad r4; The stepper motor guide rail module adopts Fu Yu FSK40-BC, and the FMC4030 guide rail controller is used as the controller of the Fu Yu FSK40-BC stepper motor guide rail module;

[0008] The PL side of the signal processing module uses the UART 16550 IP core to generate a UART interface, called the PL UART interface. The UART_RX pin of the PL UART interface is bound to the G19 pin of the XCZU9EG-2FFVG1956I chip, and the UART_TX pin is bound to the B19 pin. The G19 pin of the XCZU9EG-2FFVG1956I chip is connected to the U_TX interface of the radar RF module's transmitter, and the B19 pin of the XCZU9EG-2FFVG1956I chip is connected to the U_RX interface of the radar RF module's receiver.

[0009] The radar external trigger signal is bound to the C19 pin of the XCZU9EG-2FFVG1956I chip, and the C19 pin is connected to the external trigger pin Trig_in of the radar RF module; the radar reset signal is bound to the A12 pin of the XCZU9EG-2FFVG1956I chip, and the A12 pin is connected to the radar reset port of the radar RF module; the guide rail reset signal is bound to the B13 pin of the XCZU9EG-2FFVG1956I chip, and the B13 pin is connected to the IN0 interface of the FMC4030 guide rail controller.

[0010] Another object of the present invention is to provide a control method for a millimeter wave nondestructive testing imaging system, which is implemented using the control device of the present invention and includes the following steps:

[0011] S1. Power on the system and use the signal processing module to reset the radar and guide rail modules.

[0012] S2. Cancel the radar reset state, configure the radar working parameters, and adjust the radar working mode to external trigger mode;

[0013] S3. Start running the echo data receiving program for the radar used at the PS end of the signal processing module; the details are as follows:

[0014] S4. After data starts to be received, the radar external trigger signal is immediately sent to the radar, and the guide rail is immediately turned on to make it work;

[0015] S5: Determine whether the guide rail has completed its work. If so, jump to S6; otherwise, keep the default setting, or adjust the radar indicators as needed and jump to S5 to continue the judgment.

[0016] S6. Close the radar echo data receiving program, turn off the external trigger source, and reset the radar and guide rail.

[0017] The beneficial effects of the present invention are: the present invention is dominated by the Linux application running on the ZYNQ ARM core, and can realize the synchronous control of radar acquisition and guide rail operation in the near-field high-resolution millimeter-wave radar imaging system. The present invention first powers on the system and resets the radar, guide rail and other modules through the ZYNQ board. Then, the radar is turned on through the ZYNQ board, the radar is configured to the external trigger mode and the working parameters are configured. Then, the radar data receiving script is pulled up on the PS end of the ZYNQ board, the radar external trigger source from the ZYNQPL end is given, and the guide rail reset is canceled to start the guide rail working. Finally, after the guide rail program runs, the radar data reception is stopped and the radar is reset. Based on the radar external trigger mode and the guide rail controller, stable millimeter-wave non-destructive testing system radar acquisition and guide rail operation synchronization control are achieved, which solves the limitation of the traditional radar acquisition system that the guide rail movement and radar acquisition cannot be started synchronously, greatly simplifies the difficulty of data post-processing track calibration, and significantly shortens the imaging processing time. At the same time, relying on the advantages of the ZYNQ board, highly automated process control of the detection system is achieved, and on this basis, manual intervention during work, such as emergency stop, is supported. It has the advantages of simple operation, multiple configurable options, and is friendly to subsequent data processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a physical picture of the ZYNQ development board;

[0019] Figure 2 This is the principle block diagram of the PL side of the ZYNQ development board;

[0020] Figure 3 This is a physical picture of the system radar board;

[0021] Figure 4 This is a control flow chart of a millimeter wave nondestructive testing imaging system according to the present invention;

[0022] Figure 5 This is the imaging result of manual parameter correction. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described below with reference to the accompanying drawings.

[0024] The present invention provides a control device for a millimeter wave nondestructive testing imaging system, comprising a signal processing module, a radar radio frequency module, a guide rail controller, and a host computer instruction module respectively connected to the signal processing module; the guide rail controller is connected to the stepping motor guide rail module, and the radar radio frequency module is used to transmit and receive radar echo signals.

[0025] The signal processing module is implemented based on ALINX's AXU9EG. AXU9EG is a ZYNQ development board from ALINX that uses the XCZU9EG-2FFVG1956I chip from Xilinx's Zynq UltraScale+ MPSoCs EG series. Its PL side includes a 40-pin expansion port that supports PL-side interface expansion, enabling simultaneous startup and control of radar and guide rails based on the AXU9EG. The ZYNQ development board is shown in the figure below. Figure 1 shown.

[0026] The radar RF module uses SiRad r4; The stepper motor guide rail module adopts Fu Yu FSK40-BC, and the FMC4030 guide rail controller is used as the controller of the Fu Yu FSK40-BC stepper motor guide rail module.

[0027] The ZYNQ development board consists of two parts: the PS and the PL. The PS is the ARM processor, and the PL is the FPGA. On the PS side, the signal processing module communicates with the host computer's command module using the PS UART interface. Within the signal processing module, the GPIO interface communicates with the PL using the AXI bus protocol. The nondestructive testing system is controlled by an ARM application. The PL generates a radar external trigger signal based on GPIO input. The PS transmits a clock cycle count to the PL via GPIO0's trig_cntmax[31:0]. The PL generates a PWM wave using trig_cntmax[31:0] as the radar's external trigger signal. The PL then outputs the generated radar external trigger signal, along with the control signal received from the PS, via the 40-pin expansion port to the radar RF module and stepper motor navigation module, thus controlling the device.

[0028] The PL terminal principle block diagram of the signal processing module is as follows Figure 2As shown in the figure, the PL side uses the UART 16550 IP core to generate a UART interface, called the PL UART interface. The UART 16550 IP core is a PL-side IP core, and its input terminals communicate with the PS side via the AXI bus protocol. The output terminals (TX, RX, and GND) of the PL UART interface are all bound to the 40-pin expansion port. The PL UART interface's UART_RX is bound to the G19 pin of the XCZU9EG-2FFVG1956I chip, and its UART_TX is bound to the B19 pin. The G19 pin of the XCZU9EG-2FFVG1956I chip is connected to the U_TX interface on the radar RF module's transmitter side, and the B19 pin of the XCZU9EG-2FFVG1956I chip is connected to the U_RX interface on the radar RF module's receiver side. The radar external trigger signal is bound to the C19 pin of the XCZU9EG-2FFVG1956I chip, and the C19 pin is connected to the external trigger pin Trig_in of the radar RF module; the radar reset signal is bound to the A12 pin of the XCZU9EG-2FFVG1956I chip, and the A12 pin is connected to the radar reset port of the radar RF module; the guide rail reset signal is bound to the B13 pin of the XCZU9EG-2FFVG1956I chip, and the B13 pin is connected to the IN0 interface of the FMC4030 guide rail controller.

[0029] SiRad r4 controls the transmit pulse through the external trigger source of ZYNQ and transmits the data back to ZYNQ through the PLUART interface after ADC processing. It is powered by the Micro USB interface of the middle substrate and connected to the 40-pin expansion port of AXU9EG through the radar bottom expansion board. On the radar expansion board, the radar serial port receiving port U_TX is connected to the G19 pin of ZYNQ, and the radar serial port transmitting port U_RX is connected to the B19 pin of ZYNQ. Similarly, the radar reset port is connected to the A12 pin, and the external trigger pin Trig_in is connected to the C19 pin. The actual radar board is shown in the figure. Figure 3 shown.

[0030] The Fuyu FSK40-BC stepper motor guide rail module is controlled by the FMC4030 guide rail controller. The guide rail reset and power-up are achieved through the IN0 interface on the FMC4030. A low level on IN0 activates the guide rail, while a high level resets it. Because the IN0 interface is rated for 24V, while the B13 pin on the AXU9EG is rated for 3.3V, a relay is used to connect the B13 pin of the XCZU9EG-2FFVG1956I chip to the IN0 interface of the FMC4030 guide rail controller to achieve voltage conversion. The guide rail reset function in the PS application works by changing the pin level on the PL side via GPIO, which in turn changes the input voltage level of the IN0 interface on the FMC4030.

[0031] like Figure 4 As shown, a control method for a millimeter wave nondestructive testing imaging system of the present invention is implemented using the above-mentioned control device. The millimeter wave nondestructive testing system control framework is dominated by a Linux application on an ARM core. After the system is powered on, the application is executed in the host computer command line, including the following steps:

[0032] S1. Power on the system and use the signal processing module to reset the radar and guide rail modules. The details are as follows:

[0033] S11. Lead the AXI FPD interface of the signal processing module PS side to the PL side through the AXI_GPIO_0IP core, constrain gpio2_io_o[0] to the A12 pin of the 40-pin expansion port, and allocate address space for it; connect the A12 pin to the radar reset port of the radar RF module; SiRad The reset interface NST of the expansion board at the bottom of the r4 radar is valid at low level. When it is low, the radar does not transmit signals. When it is high, the radar works normally.

[0034] S12. Write a C++ main program in the signal processing module and use the memory mapping function mmap64() to map the actual physical memory address corresponding to the A12 pin to a virtual memory pointer. Assigning a value to the space pointed to by the virtual pointer can change the register output value of the PS side MIO pin, thereby changing the level of the A12 pin. The propagation chain of the level change on the physical link is: PS side MIO pin change -> PL side GPIO IP core output change -> A12 pin level change;

[0035] S13. Lead the AXI FPD interface on the PS side to the PL side through the AXI_GPIO_0 IP core, constrain gpio2_io_o[1] to B13 of the 40-pin expansion port, and allocate address space for it; connect the B13 pin and the GND interface of the signal processing module to the two input terminals of the relay respectively, connect the normally closed port of the relay to the IN0 interface of the FMC4030, and connect the common terminal to the GND port of the FMC4030; FMC4030 provides four guide rail program input interfaces IN0 to IN3;

[0036] S14. The guide rail program is written in advance and burned into the FMC4030 controller. Set IN0 as the program start signal, which is valid at low level.

[0037] S15. In the C++ main program, use the memory mapping function mmap64() to map the actual physical memory address corresponding to pin B13 to a virtual memory pointer. Assigning a value to the space pointed to by the virtual pointer changes the register output value of the PS side MIO pin, thereby changing the level of pin B13. In this step, the corresponding level value of B13 is set to 1, the normally closed relay is opened, and IN0 is high.

[0038] S2. Cancel the radar reset state through the signal processing module, configure the radar operating parameters, and adjust the radar operating mode to the external trigger mode; the details are as follows:

[0039] S21, set the level value corresponding to the A12 pin to 1;

[0040] S22. Connect the G19 and B19 pins of the signal processing module to the U_TX and U_RX pins of the radar RF module respectively;

[0041] S23. Store the officially provided radar configuration instructions in a text file, write an instruction sending program in the C++ main program, and write the serial port configuration and sending program operation process as a shell script. Execute the shell script with the system() function to configure the radar operating parameters through the PLUART interface.

[0042] S24. In the C++ main program, execute the echo command with the system() function to send instructions to the radar through the PL UART interface:

[0043] "TrigMode=EXT;\r\n"

[0044] Adjust the radar working mode to external trigger mode.

[0045] S3. Start running the echo data receiving program for the radar used at the PS end of the signal processing module; the details are as follows:

[0046] S31. Write a radar data serial port receiving program. The signal processing module receives radar echo data through the PLUART interface and de-protocols it to convert it into a data frame set containing only target echo information.

[0047] S32. In the C++ main program, create a radar data serial port receiving thread. In this thread, use the system() function to execute the radar data serial port receiving program written in S31 in the background and record the thread ID.

[0048] S4. After data starts to be received, the radar external trigger signal is immediately sent to the radar, and the guide rail is immediately turned on to make it work; the details are as follows:

[0049] S41、SiRad The r4 radar expansion board contains an external trigger pin, Trig_in. In external trigger mode, a rising edge triggers the radar to emit a pulse signal. The AXI FPD interface on the PS side is configured to output the external trigger source frequency division parameter, trig_cntmax. This parameter is then exported to the PL side through the AXI GPIO IP core. The PL side implements clock frequency division based on the frequency division parameter, trig_cntmax. The frequency division output, trig_out, is bound to the C19 pin of the 40-pin expansion port and assigned an address space. The C19 pin is connected to the external trigger pin, Trig_in, of the radar RF module.

[0050] S42. In the C++ main program, use the memory mapping function mmap64() to map the actual physical memory address corresponding to the AXI FPD interface to a virtual memory pointer. Assigning a value to the space pointed to by the virtual pointer changes the output value of the PS-side AXI FPD interface output register, thereby changing the external trigger source frequency. In this step, set the PS-side AXI FPD interface output to 0x001312D0, which means that the C19 output frequency is set to 40Hz, and the radar begins operation.

[0051] S43. In the C++ main program, set the level value corresponding to B13 to 0, the normally closed port of the relay is closed, IN0 is at a low level, and the guide rail starts to run.

[0052] S5: Determine whether the guide rail has completed its work. If so, jump to S6; otherwise, keep the default setting, or adjust the radar indicators as needed and jump to S5 to continue the judgment. The details are as follows:

[0053] S51. Read the output level of OUT0 of the FMC4030 controller in the C++ main program. If the output level is high, the program will automatically exit. Alternatively, you can manually enter "exit" in the command line to exit the program.

[0054] S52: If the two conditions in S51 are not met, the system parameter settings may be changed, or the default settings may be retained without change; the process then jumps to S51 to continue the judgment.

[0055] S6. Close the radar echo data receiving program, turn off the external trigger source, and reset the radar and guide rails; the details are as follows:

[0056] S61. According to the thread ID recorded in S32, find the radar echo data receiving program being executed in the background and close it through the kill() function;

[0057] S62. Set the output of the AXIFPD interface on the PS side to 0xFFFFFFFF and turn off the radar external trigger signal.

[0058] S63, set the level value corresponding to A12 to 0, and turn off the radar;

[0059] S64. Set the level value corresponding to B13 to 1, the normally closed port of the relay is opened, IN0 is high level, and the guide rail is reset.

[0060] The measured effect of this embodiment is as follows Figure 5 As shown in the figure, without the help of system synchronization control, the imaging effect when the data starting frame position is manually corrected is as follows: Figure 5 As shown in (a), it can be seen that the image is severely aliased and the target shape cannot be clearly distinguished. The control system designed by the present invention does not need to align the starting data frame position when recording data. The imaging effect diagram is as follows Figure 5 As shown in (b), it can be seen that the imaging effect is good and the target texture is clearly discernible.

[0061] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific descriptions and embodiments. Those skilled in the art can make various other specific variations and combinations based on the technical teachings disclosed in the present invention without departing from the essence of the present invention, and such variations and combinations are still within the scope of protection of the present invention.

Claims

1. A control device for a millimeter wave nondestructive testing imaging system, characterized in that: It includes a signal processing module, a radar radio frequency module, a guide rail controller, and a host computer instruction module respectively connected to the signal processing module; the guide rail controller is connected to the stepper motor guide rail module, and the radar radio frequency module is used to send and receive radar echo signals; The signal processing module uses the XCZU9EG-2FFVG1956I chip, and the radar RF module uses SiRad r4; The stepper motor guide rail module adopts Fu Yu FSK40-BC, and the FMC4030 guide rail controller is used as the controller of the Fu Yu FSK40-BC stepper motor guide rail module; The PL side of the signal processing module uses the UART 16550 IP core to generate a UART interface, called the PL UART interface. The UART_RX pin of the PLUART interface is bound to the G19 pin of the XCZU9EG-2FFVG1956I chip, and the UART_TX pin is bound to the B19 pin. The G19 pin of the XCZU9EG-2FFVG1956I chip is connected to the U_TX interface of the radar RF module's transmitter, and the B19 pin of the XCZU9EG-2FFVG1956I chip is connected to the U_RX interface of the radar RF module's receiver. The radar external trigger signal is bound to the C19 pin of the XCZU9EG-2FFVG1956I chip, and the C19 pin is connected to the external trigger pin Trig_in of the radar RF module; the radar reset signal is bound to the A12 pin of the XCZU9EG-2FFVG1956I chip, and the A12 pin is connected to the radar reset port of the radar RF module; the guide rail reset signal is bound to the B13 pin of the XCZU9EG-2FFVG1956I chip, and the B13 pin is connected to the IN0 interface of the FMC4030 guide rail controller.

2. A control method for a millimeter wave nondestructive testing imaging system, implemented using the control device of claim 1, characterized in that: The following steps are involved: S1. Power on the system and use the signal processing module to reset the radar and guide rail modules. S2. Cancel the radar reset state, configure the radar working parameters, and adjust the radar working mode to external trigger mode; S3. Start running the echo data receiving program for the radar used at the PS end of the signal processing module; the details are as follows: S4. After data starts to be received, the radar external trigger signal is immediately sent to the radar, and the guide rail is immediately turned on to make it work; S5: Determine whether the guide rail has completed its work. If so, jump to S6; otherwise, keep the default setting, or adjust the radar indicators as needed and jump to S5 to continue the judgment. S6. Close the radar echo data receiving program, turn off the external trigger source, and reset the radar and guide rail.

3. The control method for a millimeter wave nondestructive testing imaging system according to claim 2, characterized in that: The step S1 is specifically as follows: S11. Lead the AXI FPD interface of the signal processing module PS side to the PL side through the AXI_GPIO_0 IP core, constrain gpio2_io_o[0] to the A12 pin, and allocate address space for it; connect the A12 pin to the radar reset port of the radar RF module; S12, mapping the actual physical memory address corresponding to the A12 pin to the virtual memory pointer, assigning a value to the space pointed to by the virtual pointer to change the register output value of the PS end MIO pin, thereby changing the level of the A12 pin; S13. Lead the AXI FPD interface on the PS side to the PL side through the AXI_GPIO_0 IP core, constrain gpio2_io_o[1] to the B13 pin, and allocate address space for it; connect the B13 pin and the GND interface of the signal processing module to the two input terminals of the relay respectively, connect the normally closed port of the relay to the IN0 interface of the FMC4030, and connect the common terminal to the GND port of the FMC4030; S14. The guide rail program is written in advance and burned into the FMC4030 controller. Set IN0 as the program start signal, which is valid at low level. S15. Map the actual physical memory address corresponding to the B13 pin to the virtual memory pointer, assign a value to the space pointed to by the virtual pointer to change the register output value of the PS end MIO pin, and then change the level of the B13 pin; set the corresponding level value of B13 to 1, the normally closed port of the relay is opened, and IN0 is high.

4. The control method for a millimeter wave nondestructive testing imaging system according to claim 2, characterized in that: The step S2 is specifically as follows: S21, set the level value corresponding to the A12 pin to 1; S22. Connect the G19 and B19 pins of the signal processing module to the U_TX and U_RX pins of the radar RF module respectively; S23. Store the radar configuration instructions in a text file, write an instruction sending program in the C++ main program, and write the serial port configuration and sending program operation process as a shell script. Execute the shell script with the system() function to configure the radar operating parameters through the PLUART interface. S24. In the C++ main program, execute the echo command with the system() function to send instructions to the radar through the PL UART interface: "TrigMode=EXT;\r\n" Adjust the radar working mode to external trigger mode.

5. The control method for a millimeter wave nondestructive testing imaging system according to claim 2, characterized in that: The step S3 is specifically as follows: S31. Write a radar data serial port receiving program. The signal processing module receives radar echo data through the PLUART interface and de-protocols it to convert it into a data frame set containing only target echo information. S32. In the C++ main program, create a radar data serial port receiving thread. In this thread, use the system() function to execute the radar data serial port receiving program written in S31 in the background and record the thread ID.

6. The control method for a millimeter wave nondestructive testing imaging system according to claim 2, characterized in that: The step S4 is specifically as follows: S41. Set the external trigger source frequency division parameter trig_cntmax output by the AXI FPD interface on the PS side, and lead it to the PL side through the AXI GPIO IP core. The PL side implements clock frequency division based on trig_cntmax, constrains the frequency division output trig_out to the C19 pin, and allocates address space for it; connect the C19 pin to the external trigger pin Trig_in of the radar RF module; S42. Set the output of the AXIFPD interface on the PS side to 0x001312D0, that is, the output frequency of C19 is set to 40Hz, and the radar starts working; S43, set the level value corresponding to B13 to 0, the normally closed port of the relay is closed, IN0 is low level, and the guide rail starts to run.

7. The control method for a millimeter wave nondestructive testing imaging system according to claim 2, characterized in that: The step S6 is specifically as follows: S61. According to the thread ID recorded in S32, find the radar echo data receiving program being executed in the background and close it through the kill() function; S62. Set the PS-side AXI FPD interface output to 0xFFFFFFFF and disable the radar external trigger signal. S63, set the level value corresponding to A12 to 0, and turn off the radar; S64. Set the level value corresponding to B13 to 1, the normally closed port of the relay is opened, IN0 is high level, and the guide rail is reset.

Images