X-ray machine automatic positioning method and system based on electromagnetic brake current PWM closed-loop control

Abstract

According to the X-ray machine automatic positioning method and system based on electromagnetic brake current PWM closed-loop control, when the automatic positioning function of an X-ray machine bulb tube supporting system in a manual mode is achieved, the electromagnetic brake current is controlled through the PWM current closed-loop control method, and the braking force control precision is improved. According to the method, the resultant force of other forces except the braking force is obtained in a real-time iterative calculation mode, and the resultant force comprises external force acting on the bulb tube supporting system by an operator, friction force and other external force, so that interference is eliminated in the control method, and the positioning precision is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic positioning of X-ray machines, and in particular to an automatic positioning method and system of an X-ray machine based on electromagnetic brake current PWM closed-loop control. Background Art

[0002] The current X-ray tube support system can achieve automatic positioning function in manual mode through mechanical positioning or electrical braking. In the mechanical positioning mode, the tube support system is manually dragged to move toward the target position. When the mechanical detection mechanism detects that the tube support system moves to within the error range of the target position, the mechanical positioning component is activated to stop the tube support system at the target position. In the electrical braking mode, the tube support system is manually dragged to move toward the target position. When the control unit detects that it is close to the target position, the control unit controls the power device to supply or cut off current to the electrical brake (generally an electromagnetic brake), thereby activating or disabling the electrical brake and stopping the tube support system near the target position.

[0003] The mechanical positioning method requires the installation of additional mechanical detection structures and mechanical positioning mechanisms. The mechanical detection mechanism is used to detect whether the ball tube support system has moved to the target position. The mechanical positioning mechanism is used to brake the ball tube support system to stop it at the target position when the ball tube support system moves to the target position. These additional components make the mechanical structure of the ball tube support system more complicated, increase the cost, and prolong the installation time.

[0004] Although the electrical positioning method does not require additional components, it also has its own problems. First, the positioning error is large. Because when the tube support system moves to the vicinity of the target position, it still has a certain speed, and the tube support system needs to support the tube and other related components, so it has a very large mass, even up to hundreds of kilograms. This speed and large inertia of the tube support system cause it to be unable to stop moving immediately even if the brake is activated, and it often passes the target position and stops outside the positioning error range. Secondly, if the brake is activated in advance when the tube support system moves to the target position, it is difficult to determine the advance time. When the tube support system is close to the target position, the operator still applies force to the tube support system, but because the force applied by different operators is different, this operating force is difficult to estimate, and the influence of other external forces such as friction makes it difficult to estimate the brake activation time in advance. Third, because the brake does not have PWM current closed-loop control, it can only provide the maximum braking force. The brake is generally an electric brake, and the control unit only controls it to open or close, so that the braking force it provides is maximum or zero, but it cannot provide a more appropriate braking force according to the motion state of the tube support system. Fourth, the current electrical positioning method is noisy. In the current method, when the ball tube support system moves near the target position, if the control unit activates the electromagnetic brake in advance, the speed of the ball tube support system decreases. The next control cycle detects its distance from the target position. If it is predicted that the ball tube support system cannot reach the target position, the electromagnetic brake will be released. The electromagnetic brake will be activated and released multiple times before the ball tube support system stops moving. In the current method, when the electromagnetic brake is activated, it is always activated with the maximum current, and because the electromagnetic brake action surface and the brake force action surface are usually rigid bodies, the collision contact between the two will produce a large noise. Fifth, during the braking process of the ball tube support system, the control unit does not consider the external force interference such as the operating force applied to the ball tube support system by the operator in real time, resulting in poor positioning accuracy. Although the force sensor can detect the operating force applied to the ball tube support system by the operator, factors such as friction cannot be detected, and the design and installation of the force sensor will increase the complexity and cost of the system. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides an X-ray machine automatic positioning method and system based on electromagnetic brake current PWM closed-loop control. When realizing the automatic positioning function of the tube support system, the control unit iteratively calculates the braking force required by the tube support system in real time, and then applies PWM current closed-loop control of the electromagnetic brake current to control the size of the braking force to generate a braking force of appropriate size.

[0006] The specific steps include:

[0007] Step 1: Determine the position sensor, current sensor, control unit, power device and other components. The position sensor is used to detect the real-time position of the tube support system and report this position to the control unit. It is installed on the motion transmission component of the tube support system; the current sensor is used to detect the actual current of the electromagnetic brake, and it is installed in the electromagnetic brake electrical circuit; the control unit receives the signals of each sensor, and then calculates the PWM output signal of the control power device according to the following subsequent steps; the power device controls the current of the electromagnetic brake according to the PWM signal, so that the electromagnetic brake outputs the corresponding braking force; the power supply component converts the input power provided by the system into the corresponding output power, and provides power to the control unit, power device, electromagnetic brake and various sensors and other electrical components.

[0008] Step 2: First, the control unit detects whether the real-time position of the tube support system has reached the starting position point M for applying the braking force. If it has not reached point M, the control unit does not enter the automatic positioning mode, does not start the control of the electromagnetic brake, and continues to monitor the real-time position of the tube support system; if it has reached or passed point M, the real-time position parameters of the tube support system are recorded and the automatic positioning mode is entered.

[0009] Step 3: The control unit obtains the movement distance s of the tube support system from time t-1 to time t based on the feedback parameters of the position sensor r (t), the velocity v(t) of the tube support system at time t, and the velocity v(t-1) at time t-1.

[0010] Step 4: Based on the principle of Newtonian mechanics, the control unit calculates the force on the tube support system at time t as:

[0011]

[0012] Where m is the mass of the moving part of the ball-tube support system.

[0013] Step 5: The current sensor detects the actual current of the electromagnetic brake and outputs it to the control unit.

[0014] Step 6: The control unit obtains the braking force F at time t based on the relationship between the braking force and the braking current. bf (t).

[0015] Step 7: Calculate the resultant force F of the tube support system except the braking force according to the following formula: ot :

[0016] F ot (t) = F re (t)-F bf (t)

[0017] Step 8: The control unit obtains the distance s between the tube support system and the target position at time t based on the feedback from the position sensor. t (t),

[0018] Step 9: Based on the principle of Newtonian mechanics, the control unit calculates the force required for the tube support system to stop at the target position based on the current motion state parameters:

[0019]

[0020] Here, the negative sign indicates that the direction of the required force is opposite to the direction of motion;

[0021] Step 10: After the control unit calculates the force required for the tube support system to stop at the target position, it uses the following formula to obtain the braking force required to be provided by the electromagnetic brake of the tube support system at time t:

[0022] F b (t) = F n (t)-F ot (t)

[0023] Step 11: Based on the relationship between the braking force and the braking current, the control unit obtains the given current i required for the electromagnetic brake at time t b *(t);

[0024] Step 12: The control unit compares the actual electromagnetic brake current with the required given electromagnetic brake current i calculated above. b *(t) is compared to get the difference. After this difference is adjusted by PI, the duty cycle of the power device is obtained, and then the control unit outputs a PWM signal according to this duty cycle to control the on and off of the power device. When the PWM output signal is high, the power device is turned on, the voltage is applied to the electromagnetic brake winding, and the electromagnetic brake current increases; when the PWM output signal is low, the power device is disconnected, the voltage is not applied to the electromagnetic brake winding, and the electromagnetic brake current decreases. Therefore, by turning the power device on and off, the actual current of the electromagnetic brake is controlled. Based on this, a negative feedback PWM closed-loop control of the electromagnetic brake current is formed, so that the actual current of the electromagnetic brake is approximately equal to the current required to generate the required braking force, and the required braking force is obtained.

[0025] Step 13: The control unit continues to detect whether the tube support system has reached the target position point B. If not, repeat steps 3 to 13; if it has reached the target position point B, exit the automatic positioning control mode, stop the PWM output, and fully activate the electromagnetic brake to completely lock the tube support system at the target position point B.

[0026] Beneficial effects: The present invention includes the following points. First, when the ball tube support system moves to the vicinity of the target position, the control unit controls the brakes in advance according to its movement speed and the distance from the target position so that it can stop at the target position. Secondly, the control unit will calculate the braking force value required for it to reach the target position according to the motion state of the ball tube support system. Third, the present invention controls the braking current based on the PWM current closed loop to generate the braking force required by the ball tube support system, not just zero or maximum braking force. Fourth, the present invention no longer requires a separate force sensor. When calculating the braking force required by the ball tube support system, according to its motion state parameters, using the principles of Newtonian mechanics, through a real-time iterative algorithm, the resultant force of other forces acting on the ball tube support system in addition to the braking force is obtained, including the operating force applied by the operator, friction, etc., and then the braking force required to stop the ball tube support system at the target position is obtained. In this process, the force sensor output signal is no longer required.

[0027] When realizing the automatic positioning function in the manual mode of the X-ray machine tube support system, the present invention calculates the required electromagnetic braking force and electromagnetic braking current through a real-time iterative algorithm, and then applies a PWM current closed-loop control method to control the braking current, so that the electromagnetic brake outputs the required braking force, thereby increasing the braking force control accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the force diagram of the ball tube support system;

[0029] Figure 2 This is the hardware control principle block diagram;

[0030] Figure 3 It is a schematic diagram of the braking force control principle of the ball tube support system in real-time iterative calculation mode;

[0031] Figure 4 This is the flow chart of automatic positioning control of the tube support system under real-time iterative calculation mode. DETAILED DESCRIPTION

[0032] The present invention will be further explained below in conjunction with the embodiments.

[0033] The present invention is used to realize the automatic positioning function of the tube support system in manual mode. Its basic force analysis and working principle are as follows Figure 1 As shown (the ball tube support system takes the suspension system as an example). Where m is the mass of the moving part of the ball tube support system, v is the speed of the ball tube support system at the real-time position point A, point A is the real-time position point of the ball tube support system, point B is the target position point, point M is the starting point for applying the braking force, and s t is the distance between points A and B, F b is the braking force provided by the electromagnetic brake, F ris the friction force on the tube support system, F p The operating forces applied by the operator to the tube support system.

[0034] In actual application, the operator pushes the tube support system to move along the suspension track toward the target position point B. When the control unit detects that the real-time position point A of the tube support system reaches point M, the control unit starts to enter the automatic positioning mode and continuously controls the electromagnetic brake to generate appropriate braking force. At this time, the tube support system is not only affected by the operating force F applied by the operator, but also by the operating force F applied by the operator. p , which is also affected by the braking force F provided by the electromagnetic brake b , friction force F r The effect of external forces.

[0035] Figure 2 The hardware control principle block diagram is shown in FIG. The position sensor is used to detect the real-time position of the tube support system, which can be installed on the motion transmission component of the tube support system; the current sensor is used to detect the electromagnetic brake current, which is located in the electrical circuit of the electromagnetic brake; the electromagnetic brake is used to provide the corresponding braking force for the tube support system, which is controlled by the power device; the power device provides a power circuit for the electromagnetic brake, which is controlled by the control unit; the control unit is the main control component, which accepts the parameters of each sensor, and then controls the power device according to the control method of the present invention to activate or disable the electromagnetic brake; the power supply component functions to convert the input power provided by the system into the corresponding output power, and provide power to the control unit, power device, electromagnetic brake, and various sensors and other electrical components.

[0036] exist Figure 3 In the control block diagram of the braking force (here, electromagnetic braking force), i b is the braking current calculated by the control unit based on the braking force required by the tube support system, i b * is the brake given current, i bf is the brake feedback current. Based on the feedback from the position sensor, the control unit can calculate the motion parameters v (velocity) and a (acceleration) of the tube support system. In this control block diagram, v(t) and v(t-1) are the velocities of the tube support system at time t and t-1, respectively, and s t (t) is the distance between the tube support system and the target position at time t, s r (t) is the movement distance of the tube support system from time t-1 to time t, F n (t) is the braking force required for the tube support system to stop at the target position according to the motion state parameters at time t, F re (t) is the resultant force of the external force on the tube support system calculated in real time at time t, F bf(t) is the braking force provided by the electromagnetic brake of the tube support system at time t, F ot (t) is the resultant force of other forces on the tube support system at time t except the braking force, mainly including friction force, operating force applied by the operator to the tube support system, etc. b (t) is the braking force required by the tube support system at time t. F b =f(Ψ,i b ) is the functional relationship between braking force and braking current, which depends on the design parameters of the electromagnetic brake.

[0037] The basic control principle of the braking force is as follows: the control unit calculates the movement speed v(t-1) of the tube support system at time t-1, the movement speed v(t) at time t, and the movement distance s from t-1 to t based on the real-time position feedback of the position sensor. r (t). Then, based on the principles of Newtonian mechanics, the force on the tube support system at time t is calculated as:

[0038]

[0039] Then, the control unit detects the actual current of the electromagnetic brake according to the feedback of the current sensor, and obtains the braking force F at time t according to the relationship between the braking force and the braking current. bf (t). According to the following formula, the resultant force of other forces on the tube support system, in addition to the braking force, is calculated as:

[0040] F ot (t) = F re (t)-F bf (t)

[0041] In addition, the control unit obtains the distance s between the tube support system and the target position point according to the feedback from the position sensor. t (t). Based on the principle of Newtonian mechanics, the control unit calculates the force required for the tube support system to stop at the target position based on the current motion state parameters:

[0042]

[0043] The negative sign indicates that the direction of the required force is opposite to the direction of motion. Based on the above, the braking force required by the tube support system is:

[0044] F b (t) = F n (t)-F ot (t)

[0045] Then, the control unit obtains the given current i required for the electromagnetic brake at time t according to the relationship between the braking force and the braking current.b *(t). This current given value is compared with the actual brake current detected by the current sensor to obtain the difference between the two. After this difference is adjusted by PI, the duty cycle of the power switch device is obtained, and the control unit forms a PWM output signal to control the opening and closing of the power device. When the PWM output signal is high, the power device is turned on, the voltage will be applied to the electromagnetic brake winding, and the electromagnetic brake current will increase; when the PWM output signal is low, the voltage will not be applied to the electromagnetic brake winding, and the electromagnetic brake current will decrease, thereby forming an electromagnetic brake current PWM closed-loop control, so that the actual current of the electromagnetic brake is approximately equal to the required given current. Therefore, by controlling the opening and closing of the power device, the size of the actual current of the electromagnetic brake is controlled. Based on this, a negative feedback PWM closed-loop control of the electromagnetic brake current is formed, so that the actual current of the electromagnetic brake is approximately equal to the current required to generate the required braking force, and the required braking force is obtained.

[0046] Figure 4 This is a flow chart of the automatic positioning control of the tube support system in real-time iterative calculation mode. When the tube support system moves along the track to the target position in manual mode, the control process is as follows:

[0047] 1) First, the control unit detects whether the real-time position point A of the tube support system has reached the starting position point M for applying the braking force. If it has not reached point M, the control unit does not start the control of the electromagnetic brake and continues to monitor the real-time position of the tube support system. If it has reached or passed point M, the real-time position parameters of the tube support system are recorded and the automatic positioning working mode is entered.

[0048] 2) In the automatic positioning working mode, the control unit updates the position sensor parameters, obtains the real-time position of the tube support system, and calculates the movement distance s of the tube support system from time t-1 to time t r (t), the velocity v(t) of the tube support system at time t, and the velocity v(t-1) at time t-1.

[0049] 3) Based on the principle of Newtonian mechanics, the control unit calculates the resultant force on the tube support system at time t as:

[0050]

[0051] Where m is the mass of the moving part of the ball-tube support system.

[0052] 4) The control unit obtains the actual current of the electromagnetic brake according to the feedback of the current sensor.

[0053] 5) The control unit obtains the braking force F at time t based on the relationship between the braking force and the braking current. bf (t).

[0054] 6) The control unit calculates the resultant force F of the tube support system except the braking force according to the following formula ot :

[0055] F ot (t) = F re (t)-F bf (t)

[0056] 7) The control unit obtains the distance s between the tube support system and the target position point at time t based on the feedback from the position sensor. t (t),

[0057] 8) Based on the principle of Newtonian mechanics, the control unit calculates the force required for the tube support system to stop at the target position based on the current motion state parameters:

[0058]

[0059] Here, the negative sign indicates that the direction of the required force is opposite to the direction of motion;

[0060] 9) After the control unit calculates the force required for the tube support system to stop at the target position, it uses the following formula to obtain the braking force required to be provided by the electromagnetic brake of the tube support system at time t:

[0061] F b (t) = F n (t)-F ot (t)

[0062] 10) According to the relationship between braking force and braking current, the control unit obtains the given current i required for electromagnetic braking at time t b *(t);

[0063] 11) The control unit compares the actual current of the electromagnetic brake with the required given current calculated above to obtain the difference. After this difference is adjusted by PI, the duty cycle of the power device is obtained, and then the control unit outputs a PWM signal according to this duty cycle to control the on and off of the power device. When the PWM output signal is at a high level, the power device is turned on, the voltage is applied to the electromagnetic brake winding, and the electromagnetic brake current increases; when the PWM output signal is at a low level, the power device is disconnected, the voltage is not applied to the electromagnetic brake winding, and the electromagnetic brake current decreases. By controlling the on and off of the power device, the size of the actual current of the electromagnetic brake is controlled. Based on this, a negative feedback PWM closed-loop control of the electromagnetic brake current is formed, so that the actual current of the electromagnetic brake is approximately equal to the current required to generate the required braking force, thereby obtaining the required braking force.

[0064] 12) The control unit continues to detect whether the tube support system has reached the target position point B. If not, repeat the above steps 2) to 12); if it has reached the target position point B, exit the automatic positioning control mode, stop the PWM output, and fully activate the electromagnetic brake to completely lock the tube support system at the target position point B.

Claims

1. An automatic positioning method for an X-ray machine based on electromagnetic brake current PWM closed-loop control, characterized in that: The steps include: Step 1: Set up the position sensor and current sensor; the position sensor is used to detect the real-time position of the tube support system; the current sensor is used to detect the actual current of the electromagnetic brake; Step 2: The control unit detects whether the real-time position of the tube support system has reached the braking force application starting position point M. If it has not reached point M, the control unit does not enter the automatic positioning mode, does not start the control of the electromagnetic brake, and continues to monitor the real-time position of the tube support system; if it has reached or passed point M, the real-time position parameters of the tube support system are recorded, the automatic positioning mode is entered, and step 3 is executed; Step 3: The control unit obtains the movement distance s of the tube support system from time t-1 to time t based on the feedback parameters of the position sensor r (t), the velocity v(t) of the tube support system at time t and the velocity v(t-1) at time t-1; Step 4: Based on the principle of Newtonian mechanics, the control unit calculates the force on the tube support system at time t as: Where m is the mass of the moving part of the ball tube support system; Step 5: The current sensor detects the actual current of the electromagnetic brake and outputs it to the control unit; Step 6: The control unit obtains the braking force F at time t based on the relationship between the braking force and the braking current. bf (t); Step 7: Calculate the resultant force F of the tube support system except the braking force according to the following formula: ot : F ot (t)=F re (t)-F bf (t) Step 8: The control unit obtains the distance s between the tube support system and the target position at time t based on the feedback from the position sensor. t (t); Step 9: Based on the principle of Newtonian mechanics, the control unit calculates the force required for the tube support system to stop at the target position based on the current motion state parameters: Here, the negative sign indicates that the direction of the required force is opposite to the direction of motion; Step 10: After the control unit calculates the force required for the tube support system to stop at the target position, it uses the following formula to obtain the braking force required to be provided by the electromagnetic brake of the tube support system at time t: F b (t)=F n (t)-F ot (t) Step 11: Based on the relationship between the braking force and the braking current, the control unit obtains the given current i required for the electromagnetic brake at time t b *(t); Step 12: The control unit compares the actual electromagnetic brake current with the required given electromagnetic brake current i calculated above. b *(t) is compared to get the difference; after the difference is adjusted by PI, the duty cycle of the power device is obtained, and then the control unit outputs a PWM signal according to the duty cycle to control the on and off of the power device; when the PWM output signal is high, the power device is turned on, the voltage is applied to the electromagnetic brake winding, and the electromagnetic brake current increases; when the PWM output signal is low, the power device is disconnected, the voltage is not applied to the electromagnetic brake winding, and the electromagnetic brake current decreases; accordingly, a negative feedback PWM closed-loop control of the electromagnetic brake current is formed, so that the actual current of the electromagnetic brake is approximately equal to the current required to generate the required braking force, thereby obtaining the required braking force; Step 13: The control unit continues to detect whether the tube support system has reached the target position point B. If not, repeat steps 3 to 13; if it has reached the target position point B, exit the automatic positioning control mode, stop the PWM output, and fully activate the electromagnetic brake to completely lock the tube support system at the target position point B.

2. The X-ray machine automatic positioning method based on brake current PWM closed-loop control according to claim 1 is characterized in that: The position sensor is installed on the motion transmission component of the ball tube support system.

3. The X-ray machine automatic positioning method based on brake current PWM closed-loop control according to claim 1 is characterized in that: The current sensor is installed in the electromagnetic brake electrical circuit.

4. An X-ray machine automatic positioning system based on brake current PWM closed-loop control, characterized in that: It includes a position sensor, a current sensor, a control unit, a power device and a power supply component; the position sensor is used to detect the real-time position of the ball tube support system and report this position to the control unit, and it is installed on the motion transmission component of the ball tube support system; the current sensor is used to detect the actual current of the electromagnetic brake, and it is installed in the electrical circuit of the electromagnetic brake; the control unit receives the signals of each sensor, and then calculates the PWM output signal of the control power device according to any method described in claims 1-3; the power device controls the current of the electromagnetic brake according to the PWM signal, and then the electromagnetic brake outputs the corresponding braking force; the power supply component converts the input power provided by the system into the corresponding output power, and provides power to the control unit, the power device, the electromagnetic brake and each sensor.

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