Direct current fan speed control circuit and method for computed tomography

Abstract

The application discloses a DC fan speed regulation circuit and method for CT, comprising a fan motor, a motor encoder, a feedback filter circuit, a pulse conversion circuit, a speed correction circuit, a triangular wave circuit, a rotating speed parameter setting circuit, a rotating speed parameter to DC voltage circuit, an operational amplifier U1 and a fan motor controller. The single-chip microcomputer programmable program control is cancelled, the full hardware closed loop circuit is adopted to cooperate with the triangular wave reference waveform to automatically generate the PWM speed regulation, the CT fan program constant speed stable control is realized, the wiring is less, the cost is low, there is no program dead machine risk, the operation is reliable, the hardware over-temperature protection is simultaneously brought, and the CT harsh industrial heat dissipation working condition is adapted.

Description

Technical Field

[0001] This invention relates to the field of CT electric fan control technology, specifically to a DC fan speed control circuit and method for CT. Background Technology

[0002] During prolonged use, heat accumulates inside a CT (Computer-Aided Transmission) system, requiring fans to accelerate airflow for heat dissipation. Currently, the mainstream method for controlling fan speed is PWM (Pulse Width Modulation) control implemented within the MCU or FPGA program. This method is costly, has a long development cycle, and if the program malfunctions, the fan will stall. Furthermore, the code requires maintenance and downloading, and the program-controlled system necessitates additional control wiring, increasing production and subsequent maintenance costs. Summary of the Invention

[0003] The main objective of this invention is to provide a DC fan speed control circuit and method for CT scanners, in order to address the shortcomings of related technologies.

[0004] To achieve the above objectives, according to a first aspect of the present invention, a DC fan speed control circuit for a CT scanner is provided, comprising a fan motor, a motor encoder, a feedback filter circuit, a pulse conversion circuit, a speed correction circuit, a triangular wave circuit, a speed parameter setting circuit, a speed parameter to DC voltage conversion circuit, an operational amplifier U1, and a fan motor controller; wherein, the motor encoder is mounted on the fan motor, rotates synchronously with the fan motor, and outputs a speed pulse signal in real time; the speed pulse signal output terminal of the motor encoder is electrically connected in sequence to the pulse conversion circuit and the speed correction circuit, and then connected as a whole to the negative input terminal of the operational amplifier U1; the speed parameter setting circuit is electrically connected to the speed parameter to DC voltage conversion circuit, and the voltage output terminal of the speed parameter to DC voltage conversion circuit and the waveform output terminal of the triangular wave circuit are superimposed and then connected together to the positive input terminal of the operational amplifier U1; the output terminal of the operational amplifier U1 is directly connected to the input terminal of the fan motor controller, and the output terminal of the fan motor controller directly drives the fan motor.

[0005] Optionally, the pulse conversion circuit receives the speed pulse signal sent by the motor encoder and converts the speed pulse signals of different frequencies into DC signals.

[0006] Optionally, the operational amplifier U1 acquires the superimposed signal at the positive input terminal and the converted DC signal at the negative input terminal in real time; compares the potential difference between the two terminals in real time, and outputs a matching PWM waveform accordingly.

[0007] Optionally, the fan motor controller receives the PWM pulse control waveform output by the operational amplifier U1 in real time, and dynamically adjusts the effective average supply voltage applied to both ends of the fan motor according to the PWM pulse width.

[0008] Optionally, the period of the PWM waveform is locked and fixed by the triangular wave circuit. The higher the set speed parameter, the higher the overall voltage amplitude of the positive input terminal superimposed and synthesized, and the wider the PWM pulse width output by the operational amplifier U1. After being enabled by the fan motor controller, the operating speed of the fan motor increases synchronously.

[0009] Optionally, as the real-time speed of the fan motor gradually increases, the feedback voltage at the negative input terminal of the operational amplifier U1 increases synchronously, and the PWM output pulse width gradually narrows accordingly; when the feedback voltage at the negative input terminal is higher than the voltage at the peak of the triangular wave signal at the positive input terminal, the operational amplifier U1 directly returns to zero and outputs a signal. After the motor is powered off, it slowly decelerates due to its own mechanical inertia, and the synchronous feedback voltage gradually decreases accordingly.

[0010] Optionally, when the feedback voltage at the negative input terminal is lower than the voltage at the peak of the triangular wave signal, the operational amplifier U1 immediately outputs a narrow-amplitude PWM pulse width signal, which triggers the fan motor controller to restart and drive the fan motor to speed up.

[0011] According to a first aspect of the present invention, a method for controlling the speed of a DC fan used in a CT scanner is provided, characterized in that it includes: receiving a set speed parameter from the CT host via a speed parameter setting circuit, and then converting different speed parameters into a set DC voltage via a speed parameter to DC voltage conversion circuit; continuously and stably outputting a triangular wave signal via a triangular wave circuit; superimposing the set DC voltage and the triangular wave signal to synthesize a composite reference voltage, and sending it to the positive input terminal of an operational amplifier U1; the motor encoder rotating synchronously with the fan motor and outputting a pulse signal corresponding to the actual speed in real time, and the pulse conversion circuit converting the pulse signal into a feedback DC voltage; the feedback DC voltage being finely adjusted by voltage division via a speed correction circuit and then sent to the negative input terminal of the operational amplifier U1; and the operational amplifier U1 comparing the composite reference voltage at the positive input terminal with the voltage at the negative input terminal in real time, and automatically generating a PWM drive waveform with a corresponding duty cycle.

[0012] This embodiment of the CT DC fan speed control circuit includes: a fan motor, a motor encoder, a feedback filter circuit, a pulse conversion circuit, a speed correction circuit, a triangular wave circuit, a speed parameter setting circuit, a speed parameter to DC voltage conversion circuit, an operational amplifier U1, and a fan motor controller. It eliminates the need for microcontroller programmable control, employing a fully hardware closed-loop circuit with a triangular wave reference waveform to automatically generate PWM speed control. This achieves programmable constant speed control of the CT fan, reducing wiring, lowering cost, eliminating the risk of program crashes, and ensuring reliable operation. Attached Figure Description

[0013] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram of the DC fan speed control circuit for CT in an embodiment of the present invention. Detailed Implementation

[0015] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0016] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of the invention described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] According to an embodiment of the present invention, a DC fan speed control circuit for a CT scanner is provided, such as... Figure 1As shown, the system includes a fan motor, a motor encoder, a feedback filter circuit, a pulse conversion circuit, a speed correction circuit, a triangular wave circuit, a speed parameter setting circuit, a speed parameter to DC voltage conversion circuit, an operational amplifier U1, and a fan motor controller. The motor encoder is mounted on the fan motor, rotates synchronously with the fan motor, and outputs a speed pulse signal in real time. The speed pulse signal output terminal of the motor encoder is electrically connected to the pulse conversion circuit and the speed correction circuit in sequence, and then connected to the negative input terminal of the operational amplifier U1. The speed parameter setting circuit is electrically connected to the speed parameter to DC voltage conversion circuit. The voltage output terminal of the speed parameter to DC voltage conversion circuit and the waveform output terminal of the triangular wave circuit are superimposed and then connected to the positive input terminal of the operational amplifier U1. The output terminal of the operational amplifier U1 is directly connected to the input terminal of the fan motor controller, and the output terminal of the fan motor controller directly drives the fan motor.

[0019] As an optional implementation of this embodiment, the pulse conversion circuit receives the speed pulse signal sent by the motor encoder and converts the speed pulse signals of different frequencies into DC signals.

[0020] In this optional implementation, the pulse conversion circuit is directly connected to the pulse output terminal of the motor encoder, without the need for signal preprocessing. The circuit acquires the dynamic speed pulse of the fan motor in real time, and the pulse frequency increases or decreases synchronously with the fan speed, and is synchronously and linearly converted into a stable DC feedback voltage output. The higher the actual speed of the motor, the higher the encoder pulse frequency, and the higher the corresponding DC feedback voltage output to the subsequent speed correction circuit. This accurately realizes the synchronous mapping of the physical quantity of speed to the DC voltage electrical parameter, and is suitable for stable sampling in the strong electromagnetic interference environment of CT equipment.

[0021] The speed correction circuit adopts an adjustable resistor voltage divider hardware fine-tuning branch, which only needs to be calibrated once during the circuit manufacturing stage and does not need to be adjusted again during the subsequent use of the whole machine. The speed correction circuit is arranged in series between the pulse conversion circuit and the negative input terminal of the operational amplifier U1. By fine-tuning the voltage division ratio, it can compensate for individual differences of fans, batch deviations of components and line voltage drop errors, ensuring high consistency of feedback voltage for all fans at the same speed and improving the closed-loop speed control accuracy.

[0022] As an optional implementation of this embodiment, the operational amplifier U1 acquires the superimposed signal at the positive input terminal and the converted DC signal at the negative input terminal in real time; compares the potential difference between the two terminals in real time, and outputs a matching PWM waveform accordingly.

[0023] In this optional implementation, the triangular wave circuit is a pure hardware waveform generator circuit. Its core function is to continuously and stably output a standard linear triangular wave signal. The triangular wave uniformly determines the fixed working period of the entire circuit's PWM speed regulation waveform, acting as a time base ruler, eliminating the need for a chip clock or program frequency adjustment. After the external host sends the speed parameters, the speed parameter to DC voltage circuit outputs a DC voltage that corresponds one-to-one with the set speed. The faster the set speed, the higher the output DC voltage, and the slower the set speed, the lower the output DC voltage. This DC voltage is directly hardware superimposed with the triangular wave signal output by the triangular wave circuit to form a composite reference voltage, which is then fed into the positive input terminal of the operational amplifier U1. This provides a standard reference waveform support for subsequent hardware voltage comparison and automatic generation of the PWM speed regulation waveform.

[0024] The speed parameter setting circuit is a passive analog level input interface that directly connects to the speed command output of the CT host, without the need for communication lines or digital interfaces. After receiving the target speed analog command from the host, the speed parameter setting circuit sends it to the speed parameter to DC voltage conversion circuit. The speed parameter to DC voltage conversion circuit smoothly converts the speed commands of different gears into a stable DC reference voltage. The higher the speed setting, the higher the output reference voltage. This reference voltage is superimposed with the triangular wave signal and sent to the positive input of the operational amplifier U1 to form the speed control reference.

[0025] Operational amplifier U1 acquires the composite voltage signal superimposed at the positive input terminal and the real-time speed feedback DC voltage after correction at the negative input terminal in real time. The hardware compares the potential difference between the two terminals in real time and outputs a PWM waveform to match the operating conditions. The period of the PWM waveform is completely locked and fixed by the triangular wave circuit. The higher the preset speed parameter of the host, the higher the overall voltage amplitude superimposed at the positive input terminal, and the wider the PWM pulse width output by operational amplifier U1. After being empowered by the fan motor controller, the fan motor speed increases synchronously. When the PWM pulse width returns to zero, the power supply to the motor can be directly cut off. In actual closed-loop operation, as the real-time speed of the fan motor gradually increases, the feedback voltage at the negative input terminal of U1 rises synchronously and steadily, and the PWM output pulse width increases accordingly. Narrowing; when the feedback voltage at the negative input terminal is higher than the peak voltage of the triangular wave signal at the positive input terminal, U1 directly returns to zero and outputs a signal. After the motor is powered off, it slowly decelerates due to its own mechanical inertia, and the synchronous feedback voltage gradually decreases accordingly. When the feedback voltage at the negative input terminal drops slightly and is slightly lower than the peak voltage of the triangular wave signal, U1 immediately outputs a narrow-amplitude PWM pulse width signal, which links the fan motor controller to restart and drive the fan motor to speed up. The above fully automatic hardware comparison, power-off speed reduction, and power-up speed-up closed-loop action is repeated, ultimately keeping the voltage at the positive and negative input terminals of U1 dynamically equal and matching, achieving precise matching between the actual fan speed and the preset speed, and long-term stable operation at a constant speed. There is no software algorithm intervention throughout the process, eliminating speed control failure problems caused by program faults.

[0026] The fan motor controller is a power-driven switch hardware circuit without an intelligent control chip; it only performs power switch driving actions. The fan motor controller receives the PWM pulse control waveform output by the operational amplifier U1 in real time and dynamically adjusts the effective average supply voltage applied to both ends of the fan motor according to the PWM pulse width. The wider the pulse width, the higher the equivalent supply voltage of the fan motor and the faster the cooling speed. The narrower the pulse width, the lower the equivalent supply voltage and the smoother the speed drop. When the negative terminal feedback voltage exceeds the limit, the PWM pulse width returns to zero, the controller instantly cuts off the power supply to the motor, and the motor decelerates smoothly by inertia, without impact start-stop or current spikes.

[0027] For example, refer to Figure 1 As the fan motor's speed increases, the encoder outputs more pulses. These pulses are converted into DC signals by a pulse-to-DC voltage converter. The faster the fan motor, the higher the DC voltage input to the negative input of operational amplifier U1. The speed correction circuit adjusts the DC voltage applied to the negative input of U1 by adjusting the voltage superimposed on it. Once the circuit is manufactured, a speed correction is performed; no further correction is needed.

[0028] The triangular wave generation circuit produces a triangular wave. After the speed parameter is set, the speed parameter is converted into a DC voltage by the speed parameter to DC voltage circuit. This voltage is superimposed on the triangular wave and input to the positive input terminal of operational amplifier U1. The higher the speed setting, the higher the voltage value. The positive and negative input terminals of operational amplifier U1 are compared, and a PWM waveform is obtained at the output terminal of U1. This PWM signal is applied to the fan motor controller. The wider the pulse width, the faster the motor speed; when the pulse width is 0, the motor stops rotating. The period of the PWM wave is determined by the triangular wave generator circuit. As the fan motor speed gradually increases, the voltage at the negative input terminal of U1 gradually increases, and the pulse width of the PWM output from U1 gradually narrows. When the voltage at the negative input terminal of U1 is higher than the peak voltage of the triangular wave signal at the positive input terminal of U1, U2 outputs 0, and the power supply to the motor is cut off. Due to inertia, the motor continues to rotate, albeit at a gradually decreasing speed, and the voltage input to the negative input terminal of U1 gradually decreases. When the voltage at the negative input terminal of U1 is slightly lower than the peak voltage of the triangular wave signal at the positive input terminal of U1, a very narrow PWM pulse width is output to the fan motor controller, which then controls the fan motor to accelerate. When the voltage at the negative input terminal of U1 is again higher than the peak voltage of the triangular wave signal at the positive input terminal of U1, U1 outputs 0. This process repeats continuously until the voltages at the positive and negative input terminals of U1 are equal, thus ensuring that the set speed equals the actual speed. This achieves the goal of constant speed operation.

[0029] According to an embodiment of the present invention, a method for controlling the speed of a DC fan used in a CT scanner is also provided, comprising: receiving a set speed parameter from the CT host via a speed parameter setting circuit, and then converting different speed parameters into a set DC voltage via a speed parameter to DC voltage conversion circuit; continuously and stably outputting a triangular wave signal via a triangular wave circuit; superimposing the set DC voltage and the triangular wave signal to synthesize a composite reference voltage, and sending it to the positive input terminal of an operational amplifier U1; the motor encoder rotating synchronously with the fan motor and outputting a pulse signal corresponding to the actual speed in real time, and the pulse conversion circuit converting the pulse signal into a feedback DC voltage; the feedback DC voltage being finely adjusted by voltage division via a speed correction circuit and then sent to the negative input terminal of the operational amplifier U1; and the operational amplifier U1 comparing the composite reference voltage at the positive input terminal with the voltage at the negative input terminal in real time, and automatically generating a PWM drive waveform with a corresponding duty cycle.

[0030] The above description is merely an embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. A DC fan speed control circuit for CT, characterized by, It adopts a fully hardware closed-loop circuit, including: fan motor, motor encoder, feedback filter circuit, pulse conversion circuit, speed correction circuit, triangular wave circuit, speed parameter setting circuit, speed parameter to DC voltage conversion circuit, operational amplifier U1, and fan motor controller; The motor encoder is mounted on the fan motor, rotates synchronously with the fan motor, and outputs speed pulse signals in real time; The speed pulse signal output terminal of the motor encoder is electrically connected in sequence to the pulse conversion circuit and the speed correction circuit, and then connected to the negative input terminal of the operational amplifier U1. The speed parameter setting circuit is electrically connected to the speed parameter to DC voltage circuit. The voltage output terminal of the speed parameter to DC voltage circuit and the waveform output terminal of the triangular wave circuit are superimposed on each other and then connected to the positive input terminal of the operational amplifier U1. The output of the operational amplifier U1 is connected to the input of the fan motor controller, and the output of the fan motor controller directly drives the fan motor.

2. The DC fan speed control circuit for CT according to claim 1, characterized in that, The pulse conversion circuit receives the speed pulse signal sent by the motor encoder and converts the speed pulse signals of different frequencies into DC signals.

3. The DC fan speed control circuit for CT according to claim 2, characterized in that, Operational amplifier U1 acquires the superimposed signal at the positive input terminal and the converted DC signal at the negative input terminal in real time; it compares the potential difference between the two input terminals in real time and outputs a matching PWM waveform accordingly.

4. The DC fan speed control circuit for CT according to claim 3, characterized in that, The fan motor controller receives the PWM pulse control waveform output by the operational amplifier U1 in real time and dynamically adjusts the effective average power supply voltage applied to both ends of the fan motor according to the PWM pulse width.

5. The DC fan speed control circuit for CT according to claim 3 or 4, characterized in that, The PWM waveform period is locked and fixed by the triangular wave circuit. The higher the set speed parameter, the higher the overall voltage amplitude of the positive input terminal superimposed and synthesized. The wider the PWM pulse width output by the operational amplifier U1, the faster the fan motor speed will be after being enabled by the fan motor controller.

6. The DC fan speed control circuit for CT according to claim 5, characterized in that, As the real-time speed of the fan motor gradually increases, the feedback voltage at the negative input terminal of the operational amplifier U1 increases synchronously, and the PWM output pulse width gradually narrows accordingly. When the feedback voltage at the negative input terminal is higher than the voltage at the peak of the triangular wave signal at the positive input terminal, the operational amplifier U1 directly returns to zero and outputs a signal. After the motor is powered off, it slowly decelerates due to its own mechanical inertia, and the synchronous feedback voltage gradually decreases accordingly.

7. The DC fan speed control circuit for CT according to claim 6, characterized in that, When the feedback voltage at the negative input terminal is lower than the voltage at the vertex of the triangular wave signal, the operational amplifier U1 immediately outputs a narrow-amplitude PWM pulse width signal, which drives the fan motor to speed up operation by restarting the fan motor controller.

8. A method for controlling the speed of a DC fan used in a CT scanner, characterized in that, Applied to fully hardware closed-loop circuits, including: The speed parameter setting circuit receives the set speed parameters sent by the CT host, and then converts the different speed parameters into a set DC voltage through the speed parameter to DC voltage conversion circuit. The triangular wave signal is continuously and stably output through the triangular wave circuit; the set DC voltage is superimposed with the triangular wave signal to synthesize a composite reference voltage, which is then sent to the positive input terminal of the operational amplifier U1. The motor encoder rotates synchronously with the fan motor and outputs a pulse signal corresponding to the actual speed in real time. The pulse conversion circuit converts the pulse signal into a feedback DC voltage. After the feedback DC voltage is finely adjusted by voltage division through the speed correction circuit, it is sent to the negative input terminal of the operational amplifier U1. Operational amplifier U1 compares the composite reference voltage at the positive input terminal with the voltage at the negative input terminal in real time, and automatically generates the corresponding duty cycle PWM drive waveform.

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