A control circuit for a direct current brush motor and an electric hospital bed

Abstract

The application discloses a control circuit of a direct-current brush motor and an electric sickbed. The control circuit comprises an H-bridge driving circuit connected with the direct-current brush motor. The H-bridge driving circuit comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube. The control end of the second switch tube is connected with a first pull-up circuit, and the control end of the third switch tube is connected with a second pull-up circuit. The first pull-up circuit and the second pull-up circuit are connected with a first energy storage element and a second energy storage element respectively. In the case that the first power supply end is not powered, the first energy storage element and the second energy storage element supply power to the first pull-up circuit and the second pull-up circuit respectively, so that the second switch tube and the third switch tube are turned on, and the two ends of the direct-current brush motor are short-circuited. In the state that external power supply or internal power supply is available, the posture adjustment operation of the sickbed and the posture maintenance of the sickbed can be realized, and the posture of the sickbed can be maintained for a long time when there is no external power supply and the internal power supply cannot supply power.

Description

Technical Field

[0001] This application belongs to the field of medical device technology, specifically relating to a control circuit for a DC brushed motor and an electric hospital bed. Background Technology

[0002] With the improvement of people's living standards and the advancement of the healthcare industry, population aging has become a global social issue. How to address the family care and nursing needs of elderly people who are bedridden due to frailty or unable to care for themselves due to illness is a common problem faced by countries with aging populations. Due to various reasons, there is a large number of long-term bedridden patients in society. These individuals are mainly cared for by their families, which involves high costs, heavy workloads, and inadequate care conditions. Therefore, the demand for electric hospital beds is increasing daily.

[0003] Currently, most electric hospital beds on the market use electric actuators as the driving device to change the bed's posture, with safety being the primary consideration. However, since the power component of the electric actuator is a brushed motor, the torque of a brushed motor is extremely small when not driven, which reduces the locking force of the electric actuator. This makes it impossible to provide a locking force for an extended period when the battery is low or there is no power supply, resulting in the inability to maintain the current bed posture. Summary of the Invention

[0004] The purpose of this application is to provide a control circuit for a DC brushed motor and an electric hospital bed to solve the problem that existing electric hospital beds cannot provide a locking force for a long time.

[0005] To solve the above-mentioned technical problems, this application is implemented as follows:

[0006] In a first aspect, a control circuit for a brushed DC motor is provided, including an H-bridge drive circuit connected to the brushed DC motor. The H-bridge drive circuit includes a first switch, a second switch, a third switch, and a fourth switch. The first switch and the second switch constitute a first half-bridge, and the third switch and the fourth switch constitute a second half-bridge. The first half-bridge and the second half-bridge respectively control the on and off states of the two ends of the brushed DC motor.

[0007] Wherein, the first end of the first switch and the first end of the fourth switch are respectively connected to the first power supply terminal, the second end of the second switch and the second end of the third switch are respectively connected to the first common ground, one end of the DC brushed motor is respectively connected to the second end of the first switch and the first end of the second switch, and the other end of the DC brushed motor is respectively connected to the second end of the fourth switch and the first end of the third switch; the control terminal of the first switch is connected to the first control drive terminal, which is used to receive the control signal of the first switch, and the control terminal of the fourth switch is connected to the third control drive terminal, which is used to receive the control signal of the fourth switch;

[0008] The control terminal of the second switch is connected to the first pull-up circuit, and the control terminal of the third switch is connected to the second pull-up circuit. The first pull-up circuit and the second pull-up circuit are respectively connected to the first energy storage element and the second energy storage element. When there is no power supply at the first power supply terminal, the first energy storage element and the second energy storage element supply power to the first pull-up circuit and the second pull-up circuit respectively, so that the second switch and the third switch are turned on, and the two ends of the DC brushed motor are short-circuited.

[0009] Secondly, an electric hospital bed is provided, including a DC brushed motor and a control circuit for the DC brushed motor, wherein the DC brushed motor serves as a drive device for changing the posture of the hospital bed.

[0010] In this embodiment, the control terminal of the second switch in the H-bridge drive circuit of the DC brushed motor is connected to the first pull-up circuit, and the control terminal of the third switch in the H-bridge drive circuit is connected to the second pull-up circuit. The first and second pull-up circuits are connected to the first and second energy storage elements, respectively. The first and second energy storage elements supply power to the first and second pull-up circuits, respectively, so that the second and third switches are turned on. The two ends of the DC brushed motor are short-circuited, which enables the adjustment and maintenance of the bed posture when there is external or internal power supply. When there is no external power supply and the internal power supply cannot provide power, the bed posture can be maintained for a long time. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the structure of an H-bridge driving circuit provided in an embodiment of this application;

[0012] Figure 2 This is a schematic diagram of the control circuit of a DC brushed motor provided in an embodiment of this application. Detailed Implementation

[0013] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0014] The control circuit of the DC brushed motor in this embodiment includes an H-bridge drive circuit connected to the DC brushed motor. The H-bridge drive circuit includes a first switch, a second switch, a third switch, and a fourth switch. The first switch and the second switch form a first half-bridge, and the third switch and the fourth switch form a second half-bridge. The first half-bridge and the second half-bridge respectively control the on and off states of the two ends of the DC brushed motor.

[0015] Wherein, the first end of the first switch and the first end of the fourth switch are respectively connected to the first power supply terminal, the second end of the second switch and the second end of the third switch are respectively connected to the first common ground, one end of the DC brushed motor is respectively connected to the second end of the first switch and the first end of the second switch, and the other end of the DC brushed motor is respectively connected to the second end of the fourth switch and the first end of the third switch; the control terminal of the first switch is connected to the first control drive terminal, which is used to receive the control signal of the first switch, and the control terminal of the fourth switch is connected to the third control drive terminal, which is used to receive the control signal of the fourth switch;

[0016] The control terminal of the second switch is connected to the first pull-up circuit, and the control terminal of the third switch is connected to the second pull-up circuit. The first pull-up circuit and the second pull-up circuit are respectively connected to the first energy storage element and the second energy storage element. When there is no power supply at the first power supply terminal, the first energy storage element and the second energy storage element supply power to the first pull-up circuit and the second pull-up circuit respectively, so that the second switch and the third switch are turned on, and the two ends of the DC brushed motor are short-circuited.

[0017] Furthermore, a first diode is disposed between the first energy storage element and the first power supply terminal, and a second diode is disposed between the second energy storage element and the first power supply terminal.

[0018] Furthermore, the control terminal of the second switch is connected to the first terminal of the fifth switch, the second terminal of the fifth switch is connected to the second control drive terminal, and the control terminal of the fifth switch is connected to the second power supply terminal. The second control drive terminal is used to receive the control signal of the second switch. The control terminal of the third switch is connected to the first terminal of the sixth switch, the second terminal of the sixth switch is connected to the fourth control drive terminal, and the control terminal of the sixth switch is connected to the third power supply terminal. The fourth control drive terminal is used to receive the control signal of the third switch.

[0019] When the second power supply terminal and the third power supply terminal are powered, a conduction voltage is provided to the second control drive terminal and the fourth control drive terminal, and a closing voltage is provided to the first control drive terminal and the third control drive terminal, so that the fifth switch and the sixth switch are turned on, the second switch and the third switch are turned on, and the first switch and the fourth switch are not turned on.

[0020] In this configuration, both the second and third switching transistors are MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). The first terminal of both transistors is the drain, and the second terminal is the source. The control terminal of both transistors is the gate. The first and second energy storage elements are respectively a first energy storage capacitor and a second energy storage capacitor.

[0021] The control circuit of the DC brushed motor provided in this application will be described in detail below with reference to the accompanying drawings, through specific embodiments and application scenarios.

[0022] The basic components of a brushed DC motor include a stator, rotor, brushes, and commutator. The stator, composed of permanent magnets or electromagnetic windings, generates a fixed magnetic field around the rotor. The rotor (also called the armature) consists of one or more windings. When these windings are energized, they generate a magnetic field to drive the rotor to rotate. Unlike other motor types, brushed DC motors do not require a controller to switch the direction of current in the electrode windings; instead, current commutation in the DC brushed motor windings is achieved mechanically. A segmented copper bushing, called the commutator, is mounted on the shaft of the brushed DC motor. As the motor rotates, the carbon brushes slide along the commutator, contacting different segments of the commutator. These segments are connected to different rotor windings, thus, when energized through the motor's brushes, a dynamic magnetic field is generated inside the motor.

[0023] Specifically, current flows from the positive terminal of the DC power supply into the left brush. The brush contacts the commutator, and the current flows through the commutator (also called a commutator segment; the motor has two commutator segments, left and right) into the coil. The current in the coil flows back to the negative terminal of the DC power supply through the right commutator segment and the right brush, forming a closed loop. This current creates a magnetic field on the rotor. The rotor magnetic field attracts the stator magnetic field, causing the rotor to rotate. During rotor rotation, the commutator and brushes continuously excite the windings in a specific sequence, generating an alternating magnetic field that keeps the rotor rotating. When the power supply to the brushes is disconnected and the coil (rotor) is still rotating counterclockwise, short-circuiting the brushes generates a rotational force opposite to the current direction of rotation, which becomes a braking action that stops the original rotation. This is called "short-circuit braking." As the current of the brushed DC motor increases, the force required to stop its rotation also increases. Therefore, when the speed of the brushed DC motor is high, a stronger braking force will be applied; when the speed of the brushed DC motor decreases, the braking force will weaken; and when the brushed DC motor stops rotating, the braking force will become zero.

[0024] The bidirectional drive of a DC brushed motor requires an H-bridge drive circuit. The H-bridge drive circuit gets its name from its schematic diagram; it allows current in the motor windings to move in both directions. To understand this, the H-bridge drive circuit must be divided into two parts, or two half-bridges, such as... Figure 1 As shown, Q1 and Q2 form one half-bridge, while Q3 and Q4 form another. Each half-bridge can control the on / off state of one end of the BDC circuit of the brushed DC motor, making its potential either the supply voltage or ground potential. When the motor is locked without power supply, since it's impossible to directly short-circuit the motor terminals, Q2 and Q3 need to be simultaneously turned on to short-circuit ground. Turning on Q2 and Q3 requires a corresponding turn-on voltage at their gates, necessitating an energy storage element as the source of this voltage. To extend the conduction time, the selection of the lower transistor type must minimize the discharge current. MOSFETs are voltage-controlled devices, and ideally, they require no current during conduction.

[0025] In this circuit configuration, when power is available, a voltage is applied to control2 and control4 to turn on MOSFETs Q2 and Q3, thus locking the motor. Conversely, a voltage is applied to control1 and control3 to turn off MOSFETs Q1 and Q4, preventing simultaneous conduction of both transistors. However, in this configuration, without power, Q2 and Q3 are not conducting, preventing short-circuiting of the motor and thus hindering locking. Therefore, it is necessary to ensure that the gates of Q2 and Q3 are disconnected from the control terminals control2 and control4 when power is unavailable.

[0026] also, Figure 1The circuit connected to R3, R4, R5 and R6 is a protection circuit in the equivalent control terminal drive circuit. Its function is to ensure that the gate and source of the upper and lower transistors are at the same potential in the idle state, so as to prevent the upper and lower transistors of the H-bridge from conducting at the same time and damaging the H-bridge.

[0027] like Figure 2 As shown, this is a control circuit for a brushed DC motor provided in an embodiment of this application. The control circuit includes an H-bridge drive circuit connected to the brushed DC motor (BDC). The H-bridge drive circuit includes a first switch Q1, a second switch Q2, a third switch Q3, and a fourth switch Q4. The first switch Q1 and the second switch Q2 form a first half-bridge, and the third switch Q3 and the fourth switch Q4 form a second half-bridge. The first half-bridge and the second half-bridge respectively control the on and off states of the brushed DC motor (BDC).

[0028] Specifically, the first terminal of the first switch Q1 and the first terminal of the fourth switch Q4 are respectively connected to the first power supply terminal VCC; the second terminal of the second switch Q2 and the second terminal of the third switch Q3 are respectively connected to the first common ground GND; one terminal of the brushed DC motor BDC is respectively connected to the second terminal of the first switch Q1 and the first terminal of the second switch Q2; the other terminal of the brushed DC motor BDC is respectively connected to the second terminal of the fourth switch Q4 and the first terminal of the third switch Q3; the control terminal of the first switch Q1 is connected to the first control drive terminal control1, which is used to receive the control signal of the first switch Q1; the control terminal of the fourth switch Q4 is connected to the third control drive terminal control3, which is used to receive the control signal of the fourth switch Q4.

[0029] The control terminal of the second switch Q2 is connected to the first pull-up circuit, and the control terminal of the third switch Q3 is connected to the second pull-up circuit. The first and second pull-up circuits are respectively connected to the first energy storage capacitor C1 and the second energy storage capacitor C2. When there is no power supply at the first power supply terminal VCC, the first and second energy storage capacitors C1 and C2 supply power to the first and second pull-up circuits respectively, so that the second switch Q2 and the third switch Q3 are turned on, and the two ends of the DC brushed motor BDC are short-circuited. A diode D1 is provided between the first energy storage capacitor C1 and the first power supply terminal, and a diode D2 is provided between the second energy storage capacitor C2 and the first power supply terminal.

[0030] In this circuit, both the second switch Q2 and the third switch Q3 are MOSFETs. The first terminal of both the second switch Q2 and the third switch Q3 is the drain, the second terminal of both the second switch Q2 and the third switch Q3 is the source, and the control terminal of both the second switch Q2 and the third switch Q3 is the gate.

[0031] Specifically, to lock the motor, a corresponding bias voltage needs to be applied to the gates of Q2 and Q3 when there is no power supply, allowing Q2 and Q3 to conduct. Pull-up circuits are added to the gates of Q2 and Q3. After the power supply VCC is turned off, the energy storage capacitors C1 and C2 supply power to the pull-up circuits, providing a conduction voltage VCC_g to the gates of Q2 and Q3, turning on Q2 and Q3, shorting the two ends of the brushed motor, and thus locking the motor. Diodes D1 and D2 are added between the power supply and the energy storage capacitors C1 and C2 to prevent current leakage and maintain the voltage across the energy storage capacitors.

[0032] Furthermore, the control terminal of the second switch Q2 is connected to the first terminal of the fifth switch Q5, the second terminal of the fifth switch Q5 is connected to the second control drive terminal control2, and the control terminal of the fifth switch Q5 is connected to the second power supply terminal VCC_t. The second control drive terminal control2 is used to receive the control signal of the second switch Q2. The control terminal of the third switch Q3 is connected to the first terminal of the sixth switch Q6, the second terminal of the sixth switch Q6 is connected to the fourth control drive terminal control4, and the control terminal of the sixth switch Q6 is connected to the third power supply terminal VCC_t. The fourth control drive terminal control4 is used to receive the control signal of the third switch Q3.

[0033] When the second power supply terminal VCC_t and the third power supply terminal VCC_t are powered, the second control drive terminal control2 and the fourth control drive terminal control4 are provided with a turn-on voltage, and the first control drive terminal control1 and the third control drive terminal control3 are provided with a close-on voltage, so that the fifth switch Q5 and the sixth switch Q6 are turned on, the second switch Q2 and the third switch Q3 are turned on, and the first switch Q1 and the fourth switch Q4 are not turned on.

[0034] Specifically, MOSFETs Q5 and Q6 are added as switches at the control terminal, and VCC_t is the power supply that enables Q5 and Q6 to conduct when power is available. When power is available, Q5 and Q6 conduct, and the control signal can be transmitted normally. Furthermore, when the control signal is idle, the gate voltages of Q2 and Q3 can be pulled low through the pull-down circuit to keep Q2 and Q3 from conducting. When there is no power supply, Q5 and Q6 do not conduct, and the gates of Q2 and Q3 are in a high-impedance state.

[0035] In this embodiment, the control terminal of the second switch in the H-bridge drive circuit of the DC brushed motor is connected to the first pull-up circuit, and the control terminal of the third switch in the H-bridge drive circuit is connected to the second pull-up circuit. The first and second pull-up circuits are connected to the first and second energy storage elements, respectively. The first and second energy storage elements supply power to the first and second pull-up circuits, respectively, so that the second and third switches are turned on. The two ends of the DC brushed motor are short-circuited, which enables the adjustment and maintenance of the bed posture when there is external or internal power supply. When there is no external power supply and the internal power supply cannot provide power, the bed posture can be maintained for a long time.

[0036] In this embodiment, the current consumption mainly consists of the leakage current of the diode, the leakage current of the lower-side transistor of the H-bridge and the switching MOSFET, and the self-discharge of the energy storage capacitor. To determine the sustaining time of the energy storage capacitor, it is necessary to obtain the leakage current of the capacitor, the reverse leakage current of the diode, the coulombic electrons required for the gate drive of the lower-side transistor of the H-bridge, and the drain-source leakage current of the switching MOSFET. Since the conduction condition of the lower-side transistor MOSFET is that the gate and source satisfy a certain voltage difference, and the condition for forming this voltage difference is that the gate of the MOSFET acquires a sufficient amount of electrons, the total amount of electrons minus the amount of electrons acquired by the gate of the lower-side transistor MOSFET of the H-bridge is the electrical energy consumed by the lower-side transistor. To control the time for the motor to remain locked during power failure, it is necessary to select devices with appropriate leakage current and capacitors with appropriate capacitance.

[0037] Specifically, the diode has a reverse leakage current of 3pA at a reverse voltage of 20V. At 18V, the film capacitor has a leakage current of 60pA. The lower transistor in the H-bridge requires 6nC to turn on, and its Vgs(th) turn-on voltage is 1.5V. At a drain-source DC voltage of 20V, the maximum reverse leakage current of the switching transistor is 10nA. If the above components are used to build the circuit, the theoretical minimum lock-up time is 4.5 hours. To maintain a lock-up state for more than 72 hours, the capacitor capacitance should be increased to 160uF or higher.

[0038] This application embodiment also provides an electric hospital bed, including a DC brushed motor and a control circuit for the DC brushed motor as shown in Figure 2, wherein the DC brushed motor serves as a drive device for changing the posture of the hospital bed.

[0039] In this design, the motor can be locked when the electrodes of a DC brushed motor are short-circuited. In electric hospital beds, the push rod motor needs to be able to extend and retract forward and backward; therefore, a bidirectional drive circuit is required to drive the push rod motor, enabling it to be locked regardless of whether power is available or not.

[0040] Specifically, the system enables bed posture adjustment (driven by the internal motor of the electric actuator) when both external and internal power are available. When no posture adjustment is required, the system maintains the bed posture (locked by the internal motor of the electric actuator). It also maintains the bed posture (locked by the internal motor of the electric actuator) when there is no external power supply and the internal power supply is depleted or faulty. Even with the external power supply, internal battery, and control cable disconnected (no power supply), maintaining only the connection between the motor and the control system allows for motor locking for more than 72 hours.

[0041] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0042] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A control circuit for a DC brushed motor, characterized in that, The system includes an H-bridge drive circuit connected to the brushed DC motor. The H-bridge drive circuit includes a first switch, a second switch, a third switch, and a fourth switch. The first switch and the second switch form a first half-bridge, and the third switch and the fourth switch form a second half-bridge. The first half-bridge and the second half-bridge control the on and off states of the brushed DC motor, respectively. Wherein, the first end of the first switch and the first end of the fourth switch are respectively connected to the first power supply terminal, the second end of the second switch and the second end of the third switch are respectively connected to the first common ground, one end of the DC brushed motor is respectively connected to the second end of the first switch and the first end of the second switch, and the other end of the DC brushed motor is respectively connected to the second end of the fourth switch and the first end of the third switch; the control terminal of the first switch is connected to the first control drive terminal, which is used to receive the control signal of the first switch, and the control terminal of the fourth switch is connected to the third control drive terminal, which is used to receive the control signal of the fourth switch; The control terminal of the second switch is connected to the first pull-up circuit, and the control terminal of the third switch is connected to the second pull-up circuit. The first pull-up circuit and the second pull-up circuit are respectively connected to the first energy storage element and the second energy storage element. When there is no power supply at the first power supply terminal, the first energy storage element and the second energy storage element supply power to the first pull-up circuit and the second pull-up circuit respectively, so that the second switch and the third switch are turned on, and the two ends of the DC brushed motor are short-circuited. The control terminal of the second switch is connected to the first terminal of the fifth switch, the second terminal of the fifth switch is connected to the second control drive terminal, and the control terminal of the fifth switch is connected to the second power supply terminal. The second control drive terminal is used to receive the control signal of the second switch. The control terminal of the third switch is connected to the first terminal of the sixth switch, the second terminal of the sixth switch is connected to the fourth control drive terminal, and the control terminal of the sixth switch is connected to the third power supply terminal. The fourth control drive terminal is used to receive the control signal of the third switch. When the second power supply terminal and the third power supply terminal are powered, the second control drive terminal and the fourth control drive terminal are provided with a turn-on voltage, and the first control drive terminal and the third control drive terminal are provided with a close-on voltage, so that the fifth switch and the sixth switch are turned on, the second switch and the third switch are turned on, and the first switch and the fourth switch are not turned on. When there is no power supply at the first power supply terminal, the fifth and sixth switching transistors are not conducting, and the control terminals of the second and third switching transistors are in a high-impedance state.

2. The control circuit according to claim 1, characterized in that, Both the second and third switching transistors are metal-oxide-semiconductor field-effect transistors (MOSFETs). The first terminals of both the second and third switching transistors are drains, the second terminals of both the second and third switching transistors are sources, and the control terminals of both the second and third switching transistors are gates.

3. The control circuit according to claim 1, characterized in that, A first diode is disposed between the first energy storage element and the first power supply terminal, and a second diode is disposed between the second energy storage element and the first power supply terminal.

4. The control circuit according to claim 3, characterized in that, The first energy storage element and the second energy storage element are respectively the first energy storage capacitor and the second energy storage capacitor.

5. An electric hospital bed, characterized in that, It includes a DC brushed motor and a control circuit for the DC brushed motor as described in any one of claims 1 to 4, wherein the DC brushed motor serves as a drive device for changing the posture of a hospital bed.

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