Abstract:
The present invention discloses direction correcting apparatus and method thereof for a movable radiation inspecting system having a moving device. The direction correcting apparatus comprises: a direction detecting device for detecting a moving direction of the moving device and generating a detecting signal indicating the moving direction; a direction control device for controlling the moving direction of the moving device; and a control unit for calculating a deviation value between the moving direction and the predetermined direction based on the detected signal received from the direction detecting device, and the direction control device is driven according to the deviation value to correct the moving direction to the predetermined direction. The direction correcting apparatus according to the present invention can automatically control the movable radiation inspecting system to move linearly in a predetermined direction during working, which enhances automatic control degree, and has a simple structure with installing easily and reduced cost. And it also does not influence the normal running of the inspecting system on a road while not inspecting.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to a movable radiation inspecting system, a direction correcting apparatus for the movable radiation inspecting system and a direction correcting method thereof. More specifically, the invention relates to a vehicle carrying movable radiation inspecting system in which objects to be inspected, such as container/load carrying vehicle etc, are imaged by rays to inspect the objects by radiation. The invention also relates to a direction correcting apparatus for the vehicle carrying movable radiation inspecting system, in which the direction correcting apparatus automatically corrects a moving direction of a moving device of the movable radiation inspecting system to a predetermined direction when the moving direction departs away from the predetermined direction. The invention also relates to a direction correcting method for correcting a moving direction of the vehicle carrying movable radiation inspecting system. 
   BACKGROUND OF THE INVENTION 
   A vehicle carrying movable radiation inspecting system is an essential inspecting device to customs, civil airplane services and rail stations etc. for inspecting objects to be inspected, such as containers/load carrying vehicles. The vehicle carrying movable radiation inspecting system utilizes radiation imaging principle for scanning the containers/load carrying vehicles and obtaining perspective views of cargos in the containers/load carrying vehicles without opening the containers and the load carrying vehicles. And suspicious items or contraband hidden in the cargos can be found by analyzing the images thereof. 
   A movable container/load carrying vehicle inspecting system generally integrates on a vehicle. Thus, the movable radiation inspecting system is also called a scanning vehicle or vehicle carrying movable radiation inspecting system, and the vehicle is used as a moving device for the inspecting system. During inspection, the container/load carrying vehicle to be inspected stops at a given inspecting area to be scanned by the scanning vehicle. The scanning vehicle reciprocally moves in a predetermined direction parallel to the container/load carrying vehicle during scanning. 
   However, due to the uneven weight distribution of the scanning vehicle, the unevenness of the floor and inconsistency of gas pressures in the wheels etc., the moving direction of the scanning vehicle may be deviated from the predetermined direction parallel to the container/load carrying vehicle to be inspected after several scanning of the scanning vehicle. If the deviation of the moving direction of the scanning vehicle is not corrected in time, it may occur that the scanning vehicle collides with the container/load carrying vehicle. 
   To correct the deviation of the moving direction of the scanning vehicle, the conventional movable container/load carrying vehicle inspecting system has to be stopped after several scanning. And the moving direction of the scanning vehicle has to be corrected to the predetermined direction by an operator which greatly impacts the working efficiency of the system. 
   In addition, to correct the deviation of the moving direction of the scanning vehicle, a special driver is needed in the cab of the scanning vehicle, and the driver corrects the moving direction of the scanning vehicle. However, this leads to increase of manpower. And since there is scattering rays during scanning, the health of the driver may be harmed. 
   SUMMARY OF THE INVENTION 
   The present invention is provided to solve above shortcomings and problems in prior art. In an automatic correcting apparatus and method of the vehicle carrying movable radiation inspecting system which is the embodiment of the invention, no manpower is involved to automatically control the movable radiation inspecting system to maintain linear movement in a predetermined direction during working. Accordingly the automatic control degree of the whole system is increased. The invention has a simple structure with installing easily, and the cost thereof is reduced without influencing the movable radiation inspecting system running on road. 
   Accordingly, according to an aspect of the present invention, a direction correcting apparatus for a vehicle carrying movable radiation inspecting system is provided. The direction correcting apparatus comprises: a direction detecting device for detecting a moving direction of the moving device and generating a detecting signal indicating the moving direction; a direction control device for controlling the moving direction of the moving device; and a control unit for calculating a deviation value between the moving direction and the predetermined direction based on the detected signal received from the direction detecting device, and the direction control device is driven according to the deviation value to correct the moving direction to the predetermined direction. 
   Preferably, the direction correcting apparatus comprises first and second distance detectors, which generate first and second distance detecting signals respectively, wherein the control unit calculates the deviation value based on the first and second distance detecting signals. 
   Further, the first and second distance detectors detect first and second distances between the moving device and the object to be inspected. 
   Preferably, the direction correcting apparatus further comprises a reference member, wherein the first and second detectors detect the first and second distances between the moving device and the reference member. 
   Preferably, the first and second distance detectors comprise distance measuring laser sensors. 
   Preferably, the control unit comprises: an analog/digital converter which converts analog signals of the first and second distance detecting signals into digital signals; a processor which calculates the deviation value based on the first and second distance detecting signals being converted into digital signals to generate a driving signal corresponding to the deviation value; a signal driver for receiving and amplifying the driving signal; and a driving circuit for driving the direction control device based on the amplified driving signal received from the signal driver, to correct the moving direction of the moving device. 
   Further, the control unit comprises a signal isolator connected between an output of the analog/digital converter and an input of the processor to isolate input signals inputted therein and output signals outputted therefrom. 
   Further, the signal isolator comprises a photoelectric isolator. 
   Preferably, the processor comprises a MCU. 
   Preferably, the direction control device comprises: a steering wheel for controlling the moving direction of the moving device; and an actuator detachably engaged with the steering wheel and driven by the control unit, to rotate the steering wheel so that the moving direction of the moving device is controlled. 
   Further, the direction control device comprises a connecting mechanism, of which an end is connected with the actuator and the other end is detachably engaged with the steering wheel of the moving device. 
   Specifically, the connecting mechanism comprises: a connecting rod, of which an end is connected to the actuator; a post, the other end of the connecting rod is connected to the post with a joint bearing, and a top end of the post is provided with a nut for positioning the connecting rod; an installing plate, the post is provided at a top face of the installing plate, a side of the installing plate is detachably engaged with the outer periphery of the steering wheel to rotate the steering wheel. 
   Further, the direction control device comprises a bracket and a cross-shaped block, the cross-shaped block hinges with the bracket to form a gimbal, and the actuator is provided to the bracket by the cross-shaped block. 
   Specifically, the direction control device further comprises: a supporting plate on which the bracket is provided; a shielding switch provided on the supporting plate; and a pressing plate connected to the gimbal so that the pressing plate bumps against the shielding switch to power off the actuator when the actuator and the connecting mechanism both are detached from the steering wheel. 
   Preferably, the actuator comprises: a motor driven by the control unit; a worm wheel connected with an output shaft of the motor; and a worm engaged with the worm wheel, and an axial end of the worm is connected with the connecting mechanism. 
   Preferably, the actuator comprises a hydraulic cylinder driven by the control unit and a cylinder rod thereof is connected with the connecting mechanism. 
   Further, the actuator comprises a gas cylinder driven by the control unit and a cylinder rod thereof is connected with the connecting mechanism. 
   Alternatively, the direction control device comprises: a transmitting device driven by the control unit; and a flexible traction member, both ends of the flexible traction member are turned around the steering wheel, connecting to the transmitting device respectively. 
   Further, the flexible traction member is a traction rope. 
   Preferably, the traction rope is detachably engaged into a groove at the outer periphery of the steering wheel by a clipping plate and screws. 
   Preferably, the transmitting device comprises: a motor driven by the control unit; a decelerator having two output shafts driven by the motor, both ends of the traction rope are connected with the two output shafts of the decelerator having two output shafts. 
   Preferably, the transmitting device further comprises: first and second couplings, input sides of the first and second couplings are connected with two output shafts of the decelerator; first and second reel shafts, which are connected with the output sides of the first and second couplings and supported by first and second supporting bases; and first and second reels respectively provided on the first and second reel shafts, wherein both ends of the traction rope are wound around the first and second reels respectively. 
   Further, the transmitting device further comprises first and second adjusting devices for adjusting tensioning degree of the traction rope. 
   Still further, the transmitting device further comprises first and second overrunning clutches provided in the first and second couplings. 
   Preferably, the overrunning clutches comprise inner teeth ratchet overrunning clutches. Additionally, the reference member comprises an integral flat plate piece provided parallel to the predetermined direction. 
   Alternatively, the reference member comprises a plurality of flat plate segments, which are spaced apart parallel to the predetermined direction and arranged in alignment. 
   Preferably, the direction detecting device comprises at least a photoelectric switch, wherein the control unit controls the distance between the moving device and the object to be inspected within a predetermined distance based on the signals received from the at least one photoelectric switch. 
   Preferably, there are two photoelectric switches. 
   Preferably, the control unit comprises: a signal collector transmitter for collecting signals from the first and second distance detectors and the photoelectric switch; and a signal receiver for wirelessly receiving the signals transmitted from the signal collector transmitter. 
   According to a second aspect of the invention, a movable radiation inspecting system is provided, comprising the direction correcting apparatus according to the first aspect of the invention. 
   According to a third aspect of the invention, a direction correcting method for correcting the moving direction of a movable radiation inspecting system which has a moving device is provided. The direction correcting method comprising steps of: detecting step of detecting a moving direction of the moving device and generating detecting signals indicating the moving direction; calculating step of calculating a deviation value between the moving direction and a predetermined direction based on the detected signals, and automatically correcting the moving direction to the predetermined direction based on the deviation value. 
   According to the automatic direction correcting apparatus and method thereof and the movable radiation inspecting system, when the moving direction of the moving system deviates from the predetermined direction, the control unit calculates the deviation value between the moving direction and the predetermined direction based on the detected detecting signals, and the direction control device is driven based on the calculated deviation value, so that the moving direction of the moving device is corrected to the predetermined direction in order to make the moving device linearly move in the predetermined direction. 
   Therefore, when direction deviation is being corrected, the inspecting system need not to be stopped, without manpower involvement, the control unit automatically completes the direction correction, increasing work efficiency and safety performance. In addition, the structure is simple with easy assembly/disassembly and reduced cost. 
   Additionally, according to a preferred embodiment of the invention, the distance between the moving device and the object to be inspected such as a container vehicle is controlled to a predetermined distance with the two photoelectric switches, so that the relative displacement of the moving device to the object to be inspected is avoided, otherwise the object to be inspected may be damaged by bumping. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments when taken together with the accompanying drawings. 
       FIG. 1  is a schematic diagram of a direction correcting apparatus for a movable radiation inspecting system according to a first embodiment of the present invention; 
       FIG. 2  is a top view of the direction correcting apparatus of the present invention under work conditions, in which the first embodiment of a reference member is shown; 
       FIG. 3  is a top view of the direction correcting apparatus of the present invention under working conditions, in which a second embodiment of a reference member is shown; 
       FIG. 4  is a schematic plan of a direction correcting apparatus according to the second embodiment of the present invention; 
       FIG. 5  is a schematic plan of the direction control device according to the first embodiment of the present invention, in which the direction correcting apparatus is under working conditions; 
       FIG. 6  is a top schematic plan of the direction control device shown in  FIG. 5 ; 
       FIG. 7  is an enlarged schematic plan of a portion indicated with C in  FIG. 5 ; 
       FIG. 8  is a structural schematic plan of the direction control device in  FIG. 5  under non-working conditions, in which an actuator of the direction control device detaches from a steering wheel; 
       FIG. 9  is a structural schematic plan of the direction control device according to the second embodiment of the present invention; 
       FIG. 10  is a top schematic plan of the direction control device in  FIG. 9  clockwise rotating 90 degrees; 
       FIG. 11  is a structural schematic plan of a transmitting device of the direction control device in  FIG. 9 ; 
       FIG. 12  is a top schematic plan of the transmitting device in  FIG. 11 ; 
       FIG. 13  is a schematic diagram of a signal isolator according to an embodiment of the present invention; 
       FIG. 14  is a circuit schematic diagram of a signal driver according to the embodiment of the present invention; and 
       FIG. 15  is a flow chart of the direction correcting method according to the embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the embodiment of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
     FIG. 1  is a schematic diagram of a direction correcting apparatus  100  for a movable radiation inspecting system  7  according to the present invention. And  FIG. 2  is a top view of the direction correcting apparatus  100  of the present invention under working conditions. 
   In an embodiment of the present invention, the movable radiation inspecting system  7  comprises a moving device  5  for moving the whole inspecting system  7 . In other words, components of the inspecting system  7 , such as a radiation source, a detector and an imaging control system etc., are arranged on the moving device  5 , the moving device  5  may, for example, uses a vehicle, such as a motor vehicle having a chassis frame. Thus, the movable inspecting system  7  is generally termed as a scanning vehicle or a vehicle carrying movable radiation inspecting system. 
   However, it should be noted that the moving device  5  of the movable radiation inspecting system  7  is not limited to the vehicle having a chassis frame, and it can be any suitable moving vehicle in the art, such as a traction vehicle driven by a motor vehicle or other traction device. 
   As shown in  FIGS. 1-2 , the correcting apparatus  100  for the movable radiation inspecting system according to the embodiment of the present invention comprises a reference member  1 , a first distance measuring device  2   a  and a second distance measuring device  2   b  as the direction measuring device, a direction control device  4  and a control unit  3 . 
   The first and second distance measuring devices  2   a ,  2   b  are provided on the moving device  5  of the scanning vehicle with a predetermined distance L spaced apart in the moving direction A of the scanning vehicle for detecting a first distance L 1  and a second distance L 2  between the reference member  1  and the moving device  5  to generate first and second distance measuring signals. The first and second distance measuring devices  2   a ,  2   b  includes, rather than limited thereto, a laser distance measuring sensor which emits laser toward the reference member  1  so that the first and second distance L 1 , L 2  between the moving device  5  and the reference member  1  are measured. 
   In the embodiment shown in  FIGS. 1 and 2 , the first and second distance measuring devices  2   a ,  2   b  is the preferable embodiment of the direction detecting device. However, the direction detecting device is not limited to the first and second distance measuring devices  2   a ,  2   b , and it may be any device that can detect the moving direction of the moving device  5  and generate detecting signals indicating the moving direction of the moving device  5  and transmit the detected signals to the control unit  3 . For example, only one distance detector can be provided which can also achieve the correction of the deviation of the moving direction of the moving device. 
   The direction control device  4  can control the moving direction of the moving device  5 . The control unit  3  receives the first and second distance measuring signals from the first and second distance measuring devices  2   a ,  2   b , and calculates a deviation value between the moving direction A and the predetermined direction B based on the first and second distance measuring signals so that the moving direction A can be corrected to the predetermined direction B, the predetermined direction is, for example, one that parallels to the longitudinal central axis of a vehicle  6  to be inspected as an object to be inspected. 
   In the embodiment shown in  FIG. 2 , the reference member  1  is an integral flat plate which is provided in parallel to the left side of the vehicle  6  to be inspected. During the inspection of the vehicle  6  to be inspected, the scanning vehicle  7  passes between the reference member  1  and the vehicle  6  to be inspected, so that the laser emitted from the first and second distance measuring devices  2   a ,  2   b  can measure the first and second distances L 1 , L 2  in real time, and the generated first and second distance measuring signals are transmitted to the control unit  3 . 
   In the embodiment shown in  FIGS. 1 and 2 , the first and second distance measuring devices  2   a ,  2   b  transmit the first and second distance measuring signals to the control unit  3  by a cable. Alternatively, the first and second distance measuring signals can also be transmitted to the control unit  3  wirelessly (to be described in detail hereafter). 
   Alternatively, the reference member  1  in flat plate shape can also be provided at the right side of the vehicle to be inspected. During the inspection of the vehicle  6  to be inspected, the scanning vehicle  7  moves at the left side of the vehicle  6  to be inspected. At this time, the height of the reference member  1  should ensure that the laser emitted from the first and second distance measuring devices  2   a ,  2   b  can reach the reference member  1  without being blocked by the vehicle  6  to be inspected. Alternatively, the reference member  1  can also be directly provided onto the vehicle  6  to be inspected. 
   Alternatively, the reference member  1  is not necessary for the correcting apparatus  100 . For example, the moving direction of the moving device  5  can be detected by detecting a distance between the moving device  5  and the vehicle  6  to be inspected. That is to say, the vehicle  6  to be inspected can be used to replace the reference member  1  provided separately. It is appreciated that the reference member  1  can also be provided onto the vehicle  6  to be inspected. 
   It should be noted that the length of the reference member  1  is normally larger than a moving area of the scanning area of the scanning vehicle  7 , so that the laser emitted from the first and second distance measuring devices  2   a ,  2   b  can be ensured to be blocked by the reference member  1  during the whole inspection. 
   As shown in  FIG. 3 , another embodiment of the reference member  1  is shown. In the embodiment shown in  FIG. 3 , reference member  1  is a plurality of flat plate segments, such as  4  flat plate segments  1   a - 1   d  shown in  FIG. 3 , however, the present invention is not limited thereto. There may have any appropriate number of flat plate segments. The four flat plate segments  1   a - 1   d  are arranged in parallel to the predetermined direction B in a separate way and aligned with each other 
   As shown in  FIG. 1 , preferably, the control unit  3  comprises a A/D converter (analog/digital converter)  8  connected with the first and second distance measuring devices  2   a ,  2   b  by a cable, a processor  9 , a signal driver  11  and a driving circuit  12 . More preferably, the control unit  3  further comprises a signal isolator  9 . 
   The A/D converter  8  can convert analog signals of the first and second distance measuring signals from the first and second distance measuring devices  2   a ,  2   b  into digital signals, and the first and second distance measuring signals in digital signal format are transmitted to the signal isolator  9 . 
   As shown in  FIG. 13 , an embodiment of the signal isolator  9  is shown accordingly. In the embodiment shown in  FIG. 13 , the signal isolator  9  is a photoelectric isolator, which transmits electrical signals by light medium. The photoelectric isolator  9  isolates excellently the input signals inputted therein and the output electrical signals outputted therefrom. The photoelectric isolator  9  normally has three portions of light emission portion, light reception portion and signal magnification portion. And a first power supply VCC 1  and a second power supply VCC 2  are provided at the light input side and light output side. The first power supply VCC 1  and second power supply VCC 2  are connected with the photoelectric isolator  9  by first and second resistors R 1  and R 2 , respectively. The input signals drive a LED to emit light with a certain wavelength. The light is received by a light detector to generate photocurrent which is outputted after further magnification, thus completing the “electrical-photo-electrical” conversion, which functions for isolation of the input and output. Since the mutual isolation between the input and output of the photoelectric isolator  9 , the electrical signal transmission has, for example, unidirectional etc., characteristics, thus, having excellent electric insulativity and anti-interference capability. 
   In the present invention, the photoelectric isolator  9  can be any signal isolator available on market, rather than limited to the photoelectric isolator mentioned above. 
   The photoelectric isolator  9  receives digital distance detecting signals from the A/D converter  8  and sends back the signal after “electrical-photo-electric” conversion to the processor  10 . 
   According to the present invention, the processor  10  may be a Microprocessor Control Unit (MCU), a chip, a programmable logic controller (PLC), a computer, or any other proper processing device. The processor  10  receives the first and second distance measuring signals from the photoelectric isolator  9 , and calculates the deviation value between the moving direction A of the moving device  5  (i.e. the scanning vehicle  7 ) and the predetermined direction B based on the first and second distance measuring signals, thus generating driving signals corresponding to the deviation value. 
   For example, if the deviation value is zero, the processor  10  determines that the moving direction A is consistent with, i.e., parallel to, the predetermined direction B. If the deviation value is not zero, the processor  10  determines that there is a deviation between the moving direction A and the predetermined direction B, i.e., there is an angle between the moving direction A and the predetermined direction B. 
   For example, if the deviation value is positive, the processor  10  determines that the moving direction A deviates toward left with respect to the predetermined direction B in  FIGS. 2 ,  3 . If the deviation value is negative, the processor  10  determines that the moving direction A deviates toward right with respect to the predetermined direction B in  FIGS. 2 ,  3 . 
   It should be noted that the above determining method of the processor is only an example, the present invention is not limited thereto. For example, when the first and second distance measuring devices  2   a ,  2   b  are provided on the moving device  5 , even the longitudinal central axis of the moving device  5  parallels to the reference member  1 , the initial distance between the first and second distance measuring devices  2   a ,  2   b  and the reference member  1  may have error due to the installation error. However, the error thereof can be processed as the reference zero value by zero adjustment. It is appreciated for those skilled in the art that the processor  10  can calculate the deviation value based on the first and second distance detecting signals by adopting any suitable method in the art, thus determine whether the moving direction A is deviated from the predetermined direction B or not, and generates driving signals corresponding to the deviation value, thus driving the direction control device with the driving signals. For example, the processor  10  can determine whether the moving direction A is deviated from the predetermined direction B based on the comparison of the first and second distances L 1  and L 2 . 
   The signal driver  11  can receive driving signals from the processor  10  and amplifies the driving signals. 
   A schematic circuit diagram of the signal driver is shown in  FIG. 14 . In the case of the processor  10  being a MCU, driving current outputted from the MCU  10  as the driving signals is normally small, such as less than 50 mA. To drive larger load, the signal driver  11  is used for increasing the driving current outputted from the MCU  10 . For example, as shown in  FIG. 14 , after the input signal passes through the signal driver  11  configured by Darlington transistor arrays, the driving current can be amplified to 500 mA. 
   The amplified driving current is sent to the driving circuit  12  by the signal driver  11  to drive the direction control device  4 . 
   The direction correcting apparatus according to the second embodiment of the present invention will be described with reference to  FIG. 4 . As shown in  FIG. 4 , the direction correcting apparatus for a movable radiation inspecting system according to the second embodiment of the present invention comprises a first distance detector  2   a ′ and a second distance detector  2   b ′, a first photoelectric switch  45  and a second photoelectric switch  46 , a direction control device  4  (cf.  FIG. 1 ), a control unit  3  ( FIG. 1 ) and a reference member (not shown) provided at front or rear of the moving device  5 . The first distance detector  2   a ′, the second distance detector  2   b ′, the first photoelectric switch  45  and the second photoelectric switch  46  form the direction detecting device. The control unit  3  comprises a signal collector transmitter  43  and a signal receiver  44 , the remaining configuration of the control unit  3  is the same with those in the first embodiment, the description thereof is hereby omitted for clarity purpose. 
   The signal collector transmitter  43  collects signals of the first distance detector  2   a ′, the second distance detector  2   b ′, the first photoelectric switch  45  and the second photoelectric switch  46 , and sends the signals thereof to the signal receiver  44  wirelessly Then, the signal receiver  44  sends the signals received to the processor  10  by, for example, a A/D converter  8  to determine whether the moving direction A of the moving device  5  deviates from the predetermined direction or not and calculate the deviation value thereof (it should be noted that even if there is no deviation, the processor  10  can also calculate the deviation with the deviation value being zero). 
   The first photoelectric switch  45  and the second photoelectric switch  46  send, for example, on/off signals to the control unit  3  so that the control unit  3  can control the distance between the moving device  5  and the vehicle  6  to be inspected to the predetermined distance based on the signals received from the first photoelectric switch  45  and the second photoelectric switch  46  to prevent the moving device  5  displacing leftwards or rightwards in  FIG. 4  with respect to the vehicle  6  to be inspected. In other words, the control unit  3  determines whether the moving device  5  displaces with respect to the vehicle  6  to be inspected based on the signals received from the first photoelectric switch  45  and the second photoelectric switch  46 , to prevent a door shaped frame  48  of the inspecting system for imaging vehicles to be inspected from colliding with the vehicle to be inspected. 
   As shown in  FIG. 4 , the moving device  5  can be provided with a shielding member  47 . When there is no displacement of the moving device  5  with respect to the vehicle  6  to be inspected, i.e., there is a predetermined distance between the moving device  5  and the vehicle  6  to be inspected, the first photoelectric switch  45  is switched on and the second photoelectric switch  46  is shielded by the shielding member  47  (i.e., the second photoelectric switch  46  is switched off). 
   The operation of the direction correcting apparatus according to the second embodiment of the present invention will be described hereafter. 
   For example, when the moving device  5  is about to move for inspecting the vehicle  6  to be inspected, if the distance between the moving device  5  and the vehicle  6  to be inspected is larger than the predetermined distance, the first photoelectric switch  45  and the second photoelectric switch  46  both are switched off, thus it is determined by the control unit  3  that the moving device  5  is displaced leftwards in  FIG. 4  with respect to the vehicle  6  to be inspected. Then, the control unit  3  generates corresponding driving signals for driving the direction control device  4 , thus adjusting the moving direction of the moving device  5  and, further, adjusting the distance between the moving device  5  and the vehicle  6  to be inspected. When the control unit  3  receives the signals for indicating the first photoelectric switch  45  being switched on and the second photoelectric switch  46  being switched off again, the direction control device  4  is driven to be reset (i.e., the moving device  5  moves linearly in a direction in parallel to the predetermined direction). 
   When the control unit  3  receives the signals for indicating the first photoelectric switch  45  and the second photoelectric switch  46  being switched on, it is determined that the distance between the moving device  5  and the vehicle  6  to be inspected is less than the predetermined distance. At this time, the operation of the control unit  3  of adjusting the moving direction of the moving device  5  by the direction control device  4  is the reversal of the above operations, which is hereby omitted. 
   Thus, according to the second embodiment of the present invention, by the first distance detector  2   a ′, the second distance detector  2   b ′, the first photoelectric switch  45  and the second photoelectric switch  46 , not only the moving direction of the moving device  5  can be monitored in real time, but also the distance between the moving device  5  and the vehicle  6  to be inspected can be controlled. 
   It should be noted that the first distance detector  2   a ′ and the second distance detector  2   b ′ can be omitted with only the first photoelectric switch  45  and the second photoelectric switch  46  remained in the direction correcting apparatus according to the second embodiment of the present invention. In this case, the control unit  3  can determine whether the distance between the moving device  5  and the vehicle  6  to be inspected is the predetermined distance or not based on the on/off condition of the first photoelectric switch  45  and the second photoelectric switch  46 . When the distance deviates from the predetermined distance, the control unit  3  drives the direction control device  4  to change the moving direction of the moving device  5  so that the distance is adjusted to the predetermined distance. 
   Additionally, in the direction correcting apparatus according to the second embodiment of the present invention, the first photoelectric switch  45  and the second photoelectric switch  46  are arranged at a side of the moving device  5  side by side. However, it is appreciated for those skilled in the art that the arrangement of the first photoelectric switch  45  and the second photoelectric switch  46  is not limited thereto, and they may be arranged at any proper position. In addition, the number of the photoelectric switches is not limited to two, it may be any proper amount. 
   The first preferable embodiment of the direction control device  4  will be described with reference to  FIGS. 5-8 . As shown in  FIGS. 5 ,  6 , the direction control device  4  comprises a steering wheel  13  and an actuator  14  for controlling the moving direction A of the moving device  4 , such as, the steering wheel  13  can be the steering wheel of the scanning vehicle, the actuator  14  is provided at rear of the driver seat S, such as at the sidewall of the cab, which will be described in detail in the following, and extended to the steering wheel  13  from the side of the seat S to be connected with the steering wheel  13 . 
   The actuator  11  detachably is connected with the steering wheel  13 , and driven by the driving circuit  12  of the control unit  3  to rotate the steering wheel  13  so as to control the moving direction A of the moving device  5 . 
   Further, the direction control device  4  further comprises a connecting mechanism  18  with one end connected with the actuator  14  and the other end detachably connected with the steering wheel  13 . 
   More specifically, the connecting mechanism  18  comprises a connecting rod  19 , an installing plate  20 , a joint bearing  21  and a post  22 . 
   The installing plate  20  is detachably fixed to the outer periphery of the steering wheel  13  by screws. As shown in  FIG. 7 , the post  22  is provided on the upper surface of the installing plate  20 , an end of the connecting rod  19  is connected with the post  22  by the joint bearing  21  to be rotatable with respect to the post  22 . The post  22  is provided with a nut  23  on the top end for positioning the connecting rod  19 . The other end of the connecting rod  19  is hinged with the actuator  14  by a pin shaft  24  and screwed tight by a nut  25 . 
   Preferably, the direction correcting apparatus  100  according to the embodiment of the present invention further comprises an installing plate  27 , which is provided, for example, at a sidewall at the rear part of the cab of the scanning vehicle. A bracket  26  is provided on the supporting plate  27 , the actuator  14  (for example, the actuator  14  is a worm/worm shaft transmitting mechanism driven by a motor, a hydraulic cylinder, or a gas cylinder, which will be described in detail in the following) is provided on the bracket  26  by a cross shaped block  28 . The cross-shaped block  28  and the bracket  26  are hinged to form a gimbal, so that the actuator  14  can rotate with respect to the bracket  26 . 
   More preferably, a shielding switch  29  is provided on the supporting plate  27 , and a pressing plate  30  is provided at the rear end (left side in  FIGS. 5 and 6 ) of the gimbal formed by the cross-shaped block  28  and the bracket  26 . When the actuator  14  is detached from the steering wheel  13  and erected, the pressing plate  30  bumps against the shielding switch  29 , so that the actuator is switched off to stop operation, as shown in  FIG. 8 . In contrary, when the actuator  14  falls to be engaged with the steering wheel  13 , the pressing plate  30  bumps against the shielding switch  29  to switch on the actuator to supply power so that the actuator  14  can be operated, as shown in  FIGS. 5 ,  6 . 
   Preferably, the actuator  14  comprises a motor  15  driven by the driving circuit  12 , a worm wheel  16  connected with an output shaft of the motor  15 , and a worm  17  engaged with the worm wheel  16 . The worm  17  can be rotatably and detachably engaged with the steering wheel  13 , and it can be also connected by the connecting mechanism  18  mentioned above. More specifically, the worm  17  rotatably is connected with an end of the connecting rod  19  of the connecting mechanism  18 . However, to reduce cost, the worm  17  can be manufactured shorter, and a telescopic bushing (not shown) is provided between the worm  17  and the connecting rod  19 . When the worm  17  rotates, the telescopic bushing extends or retracts, to displace the connecting rod  19 , thus rotating the steering wheel  13 . 
   The driving circuit  12  drives the motor  15  according to the driving signals of the processor  10 , so that the worm wheel  16  rotates, and the worm  17  is rotated and displaced accordingly. The worm drives the connecting rod  19  to displace, so that the steering wheel  13  is rotated, thus correcting the moving direction A of the moving device  5 . 
   It is appreciated for those skilled in the art that the actuator  14  of the present invention is not limited to the motor, worm/worm wheel mechanism described above. Alternatively, the actuator  14  can be a hydraulic cylinder, which is driven by a control unit and the lever thereof is connected to a connecting mechanism such as a connecting rod  19 , thus, the steering wheel  13  is driven to rotate based on the deviation value between the moving direction A and the predetermined direction B. Further, the hydraulic cylinder can also be substituted by a gas cylinder. 
   The operation of the actuator in the manner of a hydraulic cylinder or a gas cylinder is similar to those of the actuator in the first embodiment of the present invention. For clarity purpose, the detailed description thereof is hereby omitted. 
   The second embodiment of the direction control device  4  will be described with reference to  FIGS. 9-12 . As shown in  FIGS. 9 ,  10 ,  FIG. 9  is a structural schematic plan of the direction control device  4  according to the second embodiment of present invention. And the  FIG. 10  is the top view of  FIG. 9 . The direction control device  4  according to the second embodiment of the present invention comprises a steering wheel  13 , a transmitting device  31  and a flexible traction member  32 . The transmitting device  31  is driven by the control unit  3  (driving circuit  12 ), and the flexible traction member  32  turns around the steering wheel  13 , and then both ends thereof twist to the transmitting device  31 . Preferably, the flexible traction member  32  is a traction rope. 
   More specifically, the transmitting device  31  comprises a motor  33  driven by the driving circuit  12  of the control unit  3 , a decelerator  34  having two output shafts driven by the motor  33 , first and second couplings  35   a ,  35   b  connected to the two output shafts of the decelerator  34  having two output shafts, first and second reel shafts  36   a ,  36   b  connected to the output side of the first and second couplings  35   a ,  35   b , and first and second reels  37   a ,  37   b  provided on the first and second reel shafts  36   a ,  36   b  respectively. 
   It should be noted that, if the two output shafts (i.e., the first and second reels  37   a ,  37   b ) in the decelerator  34  having two output shafts rotate in the same direction, the two ends of the traction rope  32  wind onto the first and second reels  37   a ,  37   b  in opposite direction. Conversely, if the two output shafts (i.e., the first and second reels  37   a ,  37   b ) in the decelerator  34  having two output shafts rotate in the opposite direction, both ends of the traction rope  32  wind onto the first and second reels  37   a ,  37   b  in the same direction. 
   More preferably, the transmitting device  31  further comprises first and second support seats  38   a ,  38   b , for supporting the first and second reel shafts  36   a ,  36   b  respectively, and the first and second reels  37   a ,  37   b  are provided in the first and second support seats  38   a ,  38   b . First and second overrunning clutches  39   a ,  39   b  are provided in the first and second couplings  35   a ,  35   b , preferably being inner teeth ratchet overrunning clutches. 
   Still further, first and second adjusting devices  40   a ,  40   b  are provided on the first and second support seats  38   a ,  38   b , respectively, to adjust the tension of the traction rope  32 . Preferably, the first and second adjusting devices  40   a ,  40   b  are adjusting levers, both ends of the flexible rope  32  pass through the first and second adjusting devices  40   a ,  40   b  respectively, then wind to the first and second reels  37   a ,  37   b  in opposite direction. 
   Preferably, a U shaped groove is provided at outer periphery of the steering wheel  13 , with the traction rope  32  engaged in the U shaped groove. The rope  32  is fixed by a clipping plate  41  and screws  42  to prevent the traction rope  32  detaching from the U shaped groove and sliding in the U shaped groove. In non-working conditions, such as, when a movable scanning system is required to move from one working location to another working location, the traction rope  32  is detached from the U shaped groove and operated by a driver. The transmitting device  31  is preferably provided at the rear of the seat S in the cab (the left side in  FIG. 9 ). Therefore, the driving will not be influenced after the traction rope  32  is separated from the steering wheel  13 . 
   When the moving direction A of the moving device  5  deviates from the predetermined direction B, the driving circuit  12  of the control unit  3  sends driving signals toward the motor  33  of the driving device  31 , the decelerator  34  having two output shafts is rotated by the motor  33 , so that the first and second reels  37   a ,  37   b  are rotated with an amount corresponding to the deviation value, and thus the traction rope  32  rotates the steering wheel  13 , and corrects the moving direction A of the moving device  5  to the predetermined direction B. 
   A direction correcting method for correcting direction deviation of a movable radiation inspecting system during radiation inspecting by scanning by the direction correcting apparatus according to the present invention will be described with reference to  FIG. 15 , the direction control device is the second embodiment of the direction control device shown in  FIGS. 9-12 . However, those skilled in the art will appreciate that the description of the direction correcting apparatus also applies to the first embodiment of the direction control apparatus. 
     FIG. 15  is a schematic flow chart of the direction correcting method according to the present invention. 
   As shown in  FIG. 15 , the first and second distance detectors  2   a ,  2   b  detect first and second distances L 1 , L 2  of the moving device  5  to the reference member  1  and generate first and second distance detecting signals while sending the first and second distance detecting signals to the control unit  3  (step S 1 ). 
   An A/D converter  8  of the control unit  3  converts the first and second distance detecting signals from analog signals to digital signals (step S 2 ), then the first and second distance detecting signals in digital signal format undertake “electric-photo-electric” conversion by the signal isolator  9 , then the first and second distance detecting signals are sent from the signal isolator  9  to the MCU  10  (step S 3 ). The MCU  10  determines whether the moving direction A deviates from the predetermined direction B using the first and second distance detecting signals (step S 4 ), for example, the MCU  10  determines whether the moving direction A deviates or not and the deviation direction by comparison of the difference or ratio of the first and second distances. If L 1  is larger than L 2 , for example, the moving direction A is determined to deviate toward right in  FIGS. 1-3  while the MCU  10  calculates the deviation value generating a driving signal corresponding to the deviation value, here, the term of “deviation value” includes deviation direction. If the deviation value is a negative value, for example, the moving direction A deviates clockwise with respect to the predetermined direction B, conversely, if the deviation value is a positive value, the moving direction A deviates counterclockwise with respect to the predetermined direction B. Further, if the deviation value is larger than 1, for example, the moving direction A deviates clockwise with respect to the predetermined direction B, conversely, if the deviation value is less than 1, the moving direction A deviates counterclockwise with respect to the predetermined direction B. 
   Then, the driving signals of the MCU  10  are transmitted to the signal driver  11 , which amplifies the driving signals from the MCU  10  and transmits the same to the driving circuit  12  (step S 5 ). 
   Then, the motor  33  of the direction control device  4  is rotated by the driving circuit  12 , for example, the driving motor  33  rotates counterclockwise with an angle corresponding to the deviation value, the motor  33  drives the first and second reels  37   a ,  37   b  to rotate, thus an end of the traction rope  32  is wound on, for example, the first reel  37   a , and the other end of the traction rope  32  is unwound from, for example, the second reel  37   b , and the steering wheel is driven to rotate an angle corresponding to the deviation value for correcting the moving direction A of the moving device  5  to the predetermined direction B (step S 6 ). 
   When the moving direction A is consistent with the predetermined direction B, the flow ends (step S 7 ). Otherwise, the flow chart returns to step S 1 . 
   Similarly, if the first distance L 1  is less than the second distance L 2 , it is shown the moving direction A deviates toward left from the predetermined direction B in  FIGS. 1-3 , and the control unit  3  drives the motor  33  to rotate, for example, clockwise, so that the traction rope  32  rotates the steering wheel  13 , which is similar to the operations for correcting the right deviation. Thus, the description thereof is hereby omitted. 
   It should be noted that, although  FIG. 15  shows that the process will be ended if the moving direction A is consistent with the deviation predetermined direction, the determination whether the moving direction A deviates from the predetermined direction B can be done in real time. That is to say, the first and second distance detectors  2   a ,  2   b  can detect the first and second distances L 1 , L 2  in real time. Alternatively, for example, if the reference member  1  shown in  FIG. 3  is used, the first and second distance detectors  2   a ,  2   b  intermittently detect the first and second distances L 1 , L 2 , thus periodically determine whether the moving direction deviates from the predetermined direction B or not. 
   It should be noted that if the control unit  3  (MCU  10 ) determines that the moving direction A is not deviated from the predetermined direction B based on the first and second distance detecting signals, the control unit may not transmit driving signals toward the direction control device  4 . In other words, it can also be deemed that the driving signals (driving current) transmitted from the control unit  3  toward the direction control device  4  are zero, then representing that there is no deviation. Therefore, those skilled in the art may appreciate that the control unit  3  can periodically control the direction control device  4  in real time to correct the moving direction A (when there is no deviation, the correction required is zero). 
   Additionally, those skilled in the art may appreciate that the deviation value between the moving direction A and the predetermined direction B can be set to a predetermined threshold, only when the absolute value of the deviation value is larger than the predetermined threshold, the control unit  3  controls the direction control device  4  to correct the moving direction of the moving device  5 . 
   The movable radiation inspecting system according to another aspect of the present invention comprises the above direction correcting apparatus. As for other components of the movable radiation inspecting system, such as a radiation source, a detector array provided on a telescopic arm, an imaging system, and a control system etc., they are similar to those in prior art, the components thereof are integrated on the moving device  5  to form the scanning vehicle. For simple purpose, the descriptions on the other components of the movable radiation inspecting system and the operations thereof are hereby omitted. 
   While the embodiments of the present invention have been described by way of examples taken in conjunction with the accompanying drawings, it should be appreciated that modifications, additions and variations to and from the above described embodiments may be made without deviating from the scope of the present invention which is defined by the accompanying claims.