Medical screw tightening device

Abstract

This invention provides a medical screw tightening device that reduces the burden on the operator. [Solution] The medical screw tightening device 10 comprises a DC motor 12, a battery 13 that supplies power to the DC motor 12, a control unit 14 that connects the battery 13 and the DC motor 12, a hollow cylindrical housing 11 that can be gripped by an operator and can enclose the DC motor 12, the battery 13 and the control unit 14, and a rotary tool 16 that rotates when driven by the DC motor 12, wherein the control unit 14 constantly monitors the current value supplied to the DC motor 12 and stops the DC motor 12 when the current value supplied to the DC motor 12 exceeds a preset value.

Description

Technical Field

[0001] The present invention relates to a medical screw tightening device provided with control means for a DC motor.

Background Art

[0002] Conventionally, since a DC motor can use a battery as a power source and is easily portable, as shown in Cited Document 1, it may be used as a rotational drive source of a medical screw tightening device that an operator holds by hand. The medical screw tightening device using such a DC motor is configured to adjust the maximum output of the DC motor by limiting the maximum value of the current flowing through the DC motor. However, in the conventional medical screw tightening device using a DC motor, even when a predetermined limit torque is reached, current still flows through the DC motor and rotational torque acts on the motor. Therefore, at the moment when the screw seats on the workpiece and stops rotating, a reaction acts on the hand of the operator holding the medical screw tightening device in the direction opposite to the rotational direction of the driver bit and the screw, and there are problems such as this reaction fatiguing the operator. As a result, in order to reduce the reaction, as shown in Patent Document 2, a medical screw tightening device in which the gripping portion is extended in the radial direction of the tool has become mainstream.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, extending the gripping portion radially across the driver bit increases the weight of the medical screw tightening device. This leads to problems such as increased strain on the operator's hand, especially in medical screw tightening devices that require the operator to hold the device in a fixed position for extended periods, such as those used to tighten screws into a patient's bone.

[0005] Therefore, the present invention aims to provide a medical screw tightening device that is lightweight and has minimal recoil when seated. [Means for solving the problem]

[0006] To achieve this objective, the present invention comprises a motor, a power supply for supplying power to the motor, a control unit connecting the power supply and the motor, a hollow cylindrical housing that can be gripped by an operator and can enclose the motor and the control unit, and a driver bit that rotates under the drive of the motor, wherein the control unit is configured to shut off the power supply from the power supply to the motor when the head of a screw fitted into the driver bit is seated on a bone. Furthermore, it is preferable that the control unit constantly monitors the current value supplied to the motor, and stops the motor if the current value supplied to the motor exceeds a preset limit current value. Furthermore, the control unit is configured to store a limiting current value corresponding to a predetermined tightening torque and a loss current value that occurs during the first drive after power is supplied to the power supply. It is preferable that the motor be stopped if the value obtained by subtracting the loss current value from the current value supplied to the motor exceeds the limiting current value. Furthermore, it is preferable that the control unit is configured to delete the loss current value when it is isolated from the power supply. Furthermore, it is preferable that the motor is a DC motor and the power source is a battery. Furthermore, it is preferable that the control unit stops the motor by stopping the power supply from the power source to the motor. Furthermore, it is preferable that the housing be configured in a cylindrical shape that can be grasped by an operator. [Effects of the Invention]

[0007] According to the above invention, the control unit immediately stops the motor by cutting off the power supply to it, which has advantages such as reducing the recoil acting on the worker's hand. Furthermore, if the current supplied to the motor exceeds a preset limit current value, the control unit will stop the motor, which also has advantages such as being able to tighten screws with a desired tightening torque. Furthermore, the control unit stores the value of the loss current that occurs during the first drive after power is supplied to the power supply, and is configured to stop the motor if the value obtained by subtracting the loss current value from the current value supplied to the motor exceeds a predetermined limit current value. Therefore, it is possible to determine whether the value obtained by subtracting the loss torque that occurs between the components of the medical screw tightening device from the output torque of the motor, that is, the driving torque applied to the driver bit, has reached the limit torque. As a result, it has advantages such as being able to tighten screws with accurate driving torque. Furthermore, since the control unit is configured to delete the loss current value when it is isolated from the power supply, it has advantages such as eliminating the need for calibration work. Furthermore, since the motor is a DC motor and the power source is a battery, it has advantages such as being easy to carry and improving work efficiency. Furthermore, since the control unit stops the motor by stopping the power supply from the power source to the motor, it also has advantages such as extending battery life. Furthermore, because the housing is configured in a cylindrical shape, it also has advantages such as being able to be made lighter. These effects reduce the strain on the operator's hands even during prolonged use, offering advantages such as reduced fatigue. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram showing the structure of a medical screw tightening device according to the present invention. [Figure 2] This is a block diagram showing the control configuration of a medical screw tightening device according to the present invention. [Figure 3] This graph shows the drive control of a medical screw tightening device according to the present invention. [Modes for carrying out the invention]

[0009] The first embodiment of the present invention will now be described with reference to the drawings. In Figure 1, 10 is a medical screw tightening device for fastening a screw S to an internal thread formed in a bone. This medical screw tightening device 10 has a cylindrical housing 11 that can be gripped by an operator. Inside the housing 11 are a DC motor 12, a battery 13 that supplies power to the DC motor 12, and a control unit 14 that connects the battery 13 and the DC motor 12. A gripping chuck 15 is connected to the output shaft of the DC motor 12. The tip of the gripping chuck 15 protrudes from the housing 11, and a driver bit 16 with a cross-shaped tip is gripped at the tip of the gripping chuck 15. Furthermore, the housing 11 has a lid member 111 at the end opposite to the driver bit 16 that is detachably configured, and the battery 13 is housed on the lid member 111 side. Therefore, the battery 13 can be easily removed and replaced by removing the lid member 111.

[0010] The screw S has a head S1 and a shaft S2 that are integrally formed, and a Phillips head (not shown) that can be fitted with a driver bit 16 is formed on the upper surface of the head S1, and an external thread that screws into the internal thread is formed on the outer circumference of the shaft S2.

[0011] The configuration of the control unit 14 will be described below based on Figure 2. The control unit 14 consists of a forward rotation switch 141 and a reverse rotation switch 142, a rotation command unit 143, and a rotation control unit 144. The forward rotation switch 141 and the reverse rotation switch 142 each have push-button type switches provided on the outer surface of the housing 11, and are configured to continuously output power supplied from the battery 13 to the rotation command unit 143 located downstream while the operator is pressing the push-button type switch. The rotation command unit 143 includes a conversion circuit that converts the voltage supplied from the battery 13 to a voltage suitable for the DC motor 12, and a control circuit (not shown) that connects the DC motor 12 and the battery 13 to drive in the forward direction when the forward rotation switch 141 is pressed, and connects the DC motor 12 and the battery 13 to drive in the reverse direction when the reverse rotation switch 142 is pressed. In this embodiment, the control circuit is configured to stop the DC motor 12 when neither the forward rotation switch 141 nor the reverse rotation switch 142 is pressed.

[0012] As shown in Figure 2, the rotation control unit 144 includes an interlocking switch 145 and an arithmetic processing unit 146. The interlocking switch 145 is linked to the forward rotation switch 141 and the reverse rotation switch 142, and is configured to send a forward rotation command to the arithmetic processing unit 146 when the forward rotation switch 141 is pressed, and to send a reverse rotation command to the arithmetic processing unit 146 when the reverse rotation switch 142 is pressed.

[0013] The arithmetic processing unit 146 is configured to operate the control circuit of the rotation command unit 143. When a forward rotation command is input from the interlocking switch 145, the arithmetic processing unit 146 connects the DC motor 12 and the battery 13 so that the DC motor 12 rotates in the forward direction. Conversely, when a reverse rotation command is input, the arithmetic processing unit 146 connects the DC motor 12 and the battery 13 so that the DC motor 12 rotates in the reverse direction.

[0014] Further, the arithmetic processing unit 146 stores a current value A0 corresponding to a predetermined tightening torque (hereinafter referred to as a limit current value A0) and a current value A1 when the DC motor 12 is first driven after being energized with the battery 13 (hereinafter referred to as a loss current value A1). When the battery 13 is removed from the medical screw tightening device 10 and becomes in an insulated state, the loss current value A1 is deleted.

[0015] Furthermore, the arithmetic processing unit 146 monitors a current value A2 flowing from the rotation command unit 143 toward the DC motor 12 (hereinafter referred to as an actual current value A2). As shown in FIG. 3, immediately after a current value A3 obtained by subtracting the loss current value A1 from the actual current value A2 (hereinafter referred to as a corrected current value A3) exceeds the limit current value A0, the battery 13 and the DC motor 12 are disconnected to stop the power supply to the DC motor 12. Moreover, the arithmetic processing unit 146 is configured to continue maintaining the stopped state of the DC motor 12 while the forward rotation switch 141 is pressed and a forward rotation command is input from the interlocking switch 145 even after the DC motor 12 stops.

[0016] Note that the arithmetic processing unit 146 is configured to ignore the current value supplied from the rotation command unit 143 to the DC motor 12 until a predetermined time elapses after a forward rotation command is input from the interlocking switch 145. The time is set to be longer than the time for the starting current required at the start of rotation of the DC motor 12 to converge. In the present embodiment, it is set to a very short time of 1 second or less.

[0017] Hereinafter, an operation confirmation process performed before use in surgery or the like will be described. The operator inserts a new battery 13 into the medical screw tightening device 10 that is stored with the battery 13 removed. After that, the operator presses the forward rotation switch 141 to check whether the medical screw tightening device 10 is driven in a no-load state. At this time, when a very short time has elapsed since the start of the rotational drive of the DC motor 12, the arithmetic processing unit 146 stores the loss current value A1 in the no-load state. This loss current value A1 is the sum of various current values that occur even in the no-load state due to sliding resistance generated on the torque transmission path from the DC motor 12 to the gripping chuck 15, electrical resistance inside the motor, and the like. Since the value of the current and the rotational torque of the DC motor 12 are proportional, the corrected current value A3 obtained by subtracting the loss current value A1 from the actual current value A2 is the value obtained by subtracting the torque corresponding to the loss current value A1 (hereinafter referred to as the loss torque) from the output torque of the DC motor 12, that is, the value corresponding to the driving torque actually applied to the driver bit 16 and the screw S.

[0018] The operation of the medical screw tightening device 10 configured as described above will be described. The operator fits the screw S onto the driver bit 16 of the medical screw tightening device 10 for which the operation has been confirmed, and presses the tip of the screw S against a screw opening formed in the bone in advance. In this state, when the operator presses the forward rotation switch 141, power is supplied from the battery 13 through the forward rotation switch 141 to the rotation command unit 143. The supplied power is converted by the rotation command unit 143 and then supplied to the DC motor 12 to drive the DC motor 12 in the forward rotation direction. As a result, the screw S is screwed into the screw.

[0019] As described above, after a short time has elapsed since the DC motor 12 started forward rotation, the arithmetic processing unit 146 begins monitoring the actual current value A2 flowing through the DC motor 12 and calculates a corrected current value A3 by subtracting the loss current value A1 from the actual current value A2. In this way, because the monitoring of the actual current value A2 by the arithmetic processing unit 146 is slightly delayed from the start of forward rotation of the DC motor 12, the arithmetic processing unit 146 does not measure the starting current when the DC motor 12 starts rotating. As a result, a malfunction in which the arithmetic processing unit 146 measures a starting current that greatly exceeds the limit current value A0 and stops the DC motor 12 at the same time as the DC motor 12 starts rotating is prevented. Furthermore, as the screw S is screwed in, the friction between the screw S and the bone increases, so the output torque increases, and as shown in Figure 3, the actual current value A2 and the corrected current value A3 increase.

[0020] Subsequently, when the head S1 of the screw S seats and rotation stops, the output torque increases sharply, causing the actual current value A2 supplied to the DC motor 12 to increase. As a result, as shown in Figure 3, when the corrected current value A3 exceeds the limit current value A0, the calculation processing unit 146 determines that the screw tightening is complete and stops the DC motor 12. At this time, since the calculation processing unit 146 is configured to compare the corrected current value A3 corresponding to the drive torque with the limit current value A0, the screw S can be tightened with the appropriate tightening torque without being affected by the magnitude of the torque loss.

[0021] Furthermore, the structure that abruptly stops the rotation of the DC motor 12 when the correction current value A3 exceeds the limiting current value A0 reduces the reaction torque generated in the opposite direction to the rotation of the driver bit 16 applied to the hand of the worker gripping the medical screw tightening device 10. As a result, the burden on the hand is reduced, which has the advantage of allowing the worker to use it for long periods of time during surgery, etc. Similarly, since the power supply to the DC motor 12 is cut off immediately after the rotation of the driver bit 16 stops, there is no unnecessary power consumption, which has the advantage of extending the battery life of the battery 13. The arithmetic processing unit 146 is configured to maintain the stopped state of the DC motor 12 as long as a forward rotation command is input from the interlocking switch 145 after the DC motor 12 has stopped. After that, when the worker releases the forward rotation switch 141, the stopped state is reset.

[0022] After use, the battery 13 is removed from the medical screw tightening device 10 for sterilization. As a result, the loss current value A1 stored in the calculation processing unit 146 is deleted, and a new loss current value A1 is acquired during the next operational check. In this way, the medical screw tightening device 10 acquires a loss current value A1 that corresponds to the loss torque which changes due to variations in the characteristics of the components of the medical screw tightening device 10 and the degree of deterioration of the components during the operational check performed immediately before surgery. Therefore, during surgery, the medical screw tightening device 10 can accurately measure the driving torque actually applied to the driver bit 16 and the screw S. As a result, the medical screw tightening device 10 does not require periodic calibration.

[0023] It should be noted that the medical screw tightening device 10 according to the present invention is not limited to the one described above, and various modifications are possible without departing from the spirit of the invention. For example, the driver bit 16 is preferably changed as appropriate to match the screw S to be tightened, and the tip can be a hexagonal shape, a hexalobular shape, or any other shape other than a tenth-order shape. Similarly, the switches 141 and 142 can be slide switches, rocker switches, or other switches other than push-button switches. Also, the battery 13 is an example of a power source, and can be either a primary or secondary battery. Furthermore, in the above embodiment, the medical screw tightening device 10 was configured to monitor the value of the current, but it can also be configured to monitor the rotational torque by providing a torque sensor on the rotational drive path. [Explanation of Symbols]

[0024] 10… Medical screw tightening device 11… Cabinet 111… Lid component 12… DC motor 13...battery 14 ... Control Unit 141... Forward rotation switch 142... Reverse switch 143… Rotation command unit 144… Rotation control unit 145… Interlocking switch 146… Processing Unit 15… Gripping chuck 16… Driver bits A0 ... Limiting current value A1 ... Current loss value A2 ... Actual current value A3 ... Correction current value S... screw S1 … Head S2 … Shaft part

Claims

1. Motor and, A power supply for the motor, A control unit that connects the power supply and the motor, A hollow cylindrical housing that can be grasped by an operator and that can enclose the motor and the control unit, The system includes a driver bit that rotates under the drive of the motor, The control unit is configured to shut off the power supply from the power source to the motor when the head of the screw that fits into the driver bit is seated in the bone, making it a medical screw tightening device.

2. The medical screw tightening device according to claim 1, characterized in that the control unit constantly monitors the current value supplied to the motor and stops the motor when the current value supplied to the motor exceeds a preset limit current value.

3. The control unit is configured to store a limiting current value corresponding to a predetermined tightening torque and a loss current value that occurs during the first drive after power is supplied to the power supply, and the motor is stopped when the value obtained by subtracting the loss current value from the current value supplied to the motor exceeds the limiting current value, as described in claim 2.

4. The medical screw tightening device according to claim 3, characterized in that the control unit is configured to delete the loss current value when it is isolated from the power supply.

5. The medical screw tightening device according to claim 1, characterized in that the motor is a DC motor and the power source is a battery.

6. The medical screw tightening device according to claim 5, characterized in that the control unit stops the motor by stopping the power supply from the power source to the motor.

7. The medical screw tightening device according to claim 1, characterized in that the housing is configured in a cylindrical shape that can be grasped by an operator.

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