Medical electric tapper

Abstract

To provide a medical electric tapper with low burden on an operator.SOLUTION: A medical electric tapper includes: a motor 12; a power supply 13 that supplies power to the motor; a control unit 14 that connects the power supply with the motor 12; a housing 15 that can enclose the motor and the control unit; and a tap bit 16 that applies female screw processing to a bone W by rotating in response to driving of the motor. The control unit is configured to block power supply from the power supply to the motor when the tap bit has entered the bone by a predetermined depth. The tap bit includes: a tap part 161 that applies female screw processing to the bone; and a stopper 162 that makes contact with a surface of the bone when the tap part has entered the bone by the predetermined depth. When detecting that the stopper is in contact with the bone, the control unit stops rotation of the motor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention provides a medical electric tapper that places less strain on the operator's hands. [Background technology]

[0002] Conventionally, a known power tool that is rotated by a motor is a power tool held by an operator, as described in Patent Document 1. Such a power tool is configured to control the maximum torque of the motor by controlling the upper limit of the current supplied to the motor, which allows a screw to be fastened to a workpiece with a predetermined torque. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4203268 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional power tools, current continues to flow through the motor even after the maximum torque is reached, and the motor continues to generate rotational torque. As a result, when the rotary tool is forced to stop rotating due to the contact of the screw bearing surface or tap bit with the workpiece, a reaction force acts on the hand of the operator holding the power tool in the direction opposite to the rotation of the rotary tool, causing fatigue and other problems. For this reason, conventional power tools are unsuitable for use as medical electric tappers in precise, long-term applications such as surgery.

[0005] Therefore, an object of the present invention is to provide a medical electric tapper that has little recoil when internal thread processing is completed. [Means for solving the problem]

[0006] To achieve this objective, the present invention comprises a motor, a power source that supplies power to the motor, a control unit that connects the power source and the motor, a housing that can be held by an operator and that can contain the motor and control unit, and a tap bit that rotates when driven by the motor to create an internal thread in the bone, and the control unit is configured to cut off the power supply from the power source to the motor when the tap bit penetrates the bone to a predetermined depth. It is preferable that the tap bit has a tap portion that processes the bone into an internal thread, and a stopper that is located proximal to the tap portion and abuts against the surface of the bone when the tap portion penetrates into the bone to a predetermined depth, and that the control unit stops the rotation of the motor when it detects that the stopper has abutted against the bone. It is also preferable that the control unit constantly monitors the load current value supplied to the motor, and cuts off the current supplied to the motor when the increase in the load current value per unit time exceeds a predetermined value. Furthermore, the motor is preferably a DC motor. Moreover, it is preferable that the housing is configured in a cylindrical shape that can be held by an operator. [Effects of the Invention]

[0007] According to the above invention, the control unit cuts off the power supply to the motor to immediately stop the motor, which has the advantage of reducing the reaction force acting on the operator's hands. In addition, the tap bit has a tap portion and a stopper, and when the tap portion is threaded to a predetermined depth, the stopper abuts the bone, which has the advantage of preventing the thread from being threaded too deeply. The control unit is also configured to cut off the current supplied to the motor when the increase in the current value supplied to the motor per unit time exceeds a predetermined value. Therefore, when the stopper abuts against the bone and the current value supplied to the motor increases sharply, the control unit can cut off the power supply to the motor and stop the motor. As a result, there is an advantage in that it is possible to detect that the stopper has abutted against the bone regardless of the length of the tap bit or the structure of the bone. Furthermore, since the motor is a DC motor, a battery can be used as the power source, which has the advantage of improving workability. Moreover, since the housing is configured in a cylindrical shape, there is also the advantage that it is possible to reduce the weight. These effects reduce the strain on the operator's hands even when operating for a long period of time, and also provide the advantage of reducing fatigue even when operating for a long period of time. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic side view showing the structure of a medical electric tapper according to the present invention. FIG. [Figure 2] 1 is a block diagram showing the control configuration of a medical electric tapper according to the present invention; [Figure 3] 1A and 1B are diagrams showing the state of internal thread machining by a medical electric tapper according to the present invention, in which (a) is an enlarged schematic side view of the main part showing the state of internal thread machining in a bone in which the cortical bone is thicker than the tap portion, and (b) is a graph showing the drive control of the medical electric tapper in the state of internal thread machining shown in (a). [Figure 4] 1A and 1B are diagrams showing the state of internal thread machining by a medical electric tapper according to the present invention, in which (a) is an enlarged schematic side view of the main part showing the state of internal thread machining in a bone in which the cortical bone is thinner than the tap portion, and (b) is a graph showing the drive control of the medical electric tapper in the state of internal thread machining shown in (a). [Figure 5]10A and 10B are diagrams showing the state of internal thread machining by a second embodiment of the medical electric tapper according to the present invention, in which (a) is an enlarged schematic side view of the main part showing the state of internal thread machining in a bone in which the cortical bone is thicker than the tap portion, and (b) is a graph showing the drive control of the medical electric tapper in the internal thread machining state shown in (a). [Figure 6] 10A and 10B are diagrams showing the internal thread machining state by a second embodiment of the medical electric tapper according to the present invention, in which (a) is an enlarged schematic side view of the main part showing the internal thread machining state in a bone in which the cortical bone is thinner than the tap portion, and (b) is a graph showing the drive control of the medical electric tapper in the internal thread machining state shown in (a). [Figure 7] 1( a ) and 1 ( b ) are enlarged schematic side views of essential parts showing another embodiment of the medical electric tapper according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] A first embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 10 denotes an example of a medical electric tapper for drilling a female thread into a pilot hole formed in a bone W. The medical electric tapper 10 has a cylindrical housing 11 that can be held by an operator. Housing 11 houses 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 to the DC motor 12. A gripping chuck 15 is connected to an output shaft 121 of the DC motor 12. The tip of the gripping chuck 15 protrudes from the housing 11, and a tap bit 16 is gripped by the gripping chuck 15. The tap bit 16 has a male-threaded tap portion 161 provided at its tip and a stopper 162 that is larger than the tap portion 161 and provided proximal to the tap portion 161. 3(a), when the tap portion 161 penetrates the bone W to a predetermined depth, the stopper 162 comes into contact with the surface of the bone W. Furthermore, the end of the housing 11 opposite the tap bit 16 is a detachable cover member 111, and the battery 13 is housed on the cover member 111 side. Therefore, by removing the cover member 111, the battery 13 can be easily removed and replaced.

[0010] The configuration of the control unit 14 will be described below with reference to FIG. The control unit 14 is composed of a forward rotation switch 141, 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 a push button switch provided on the outer periphery of the housing 11, and are configured to continuously output power supplied from the battery 13 to the downstream rotation command unit 143 while the operator presses the push button 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 rotate in the forward direction when the forward rotation switch 141 is pressed, and connects the DC motor 12 and the battery 13 to rotate in the reverse direction when the reverse switch 142 is pressed. Note that the control circuit in this embodiment is configured to stop the DC motor 12 when neither the forward rotation switch 141 nor the reverse rotation switch 142 is pressed.

[0011] The rotation control unit 144 is configured to disconnect the battery 13 and the DC motor 12 and stop the power supply to the DC motor 12 immediately after the stopper 162 abuts against the bone, and as shown in FIG. 2, includes an interlocking switch 145 interlocked with the forward rotation switch 141 and the reverse rotation switch 142, and an arithmetic processing unit 146. The interlocking switch 145 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. The arithmetic processing unit 146 is also configured to be able to operate the control circuit of the rotation command unit 143, and is configured to connect the DC motor 12 and the battery 13 so that the DC motor 12 rotates in the forward direction when a forward rotation command is input from the interlocking switch 145, and to connect the DC motor 12 and the battery 13 so that the DC motor 12 rotates in the reverse direction when the reverse rotation command is input. Furthermore, after a predetermined time has elapsed since a forward rotation command was input from the interlocking switch 145, the arithmetic processing unit 146 monitors the current value supplied from the rotation command unit 143 to the DC motor 12, calculates the increase in the current value per unit time, and controls the DC motor 12 to stop within the control circuit when the increase exceeds a predetermined value.

[0012] The arithmetic processing unit 146 is configured not to stop the DC motor 12 even if the current value supplied to the DC motor 12 from the rotation command unit 143 suddenly increases until a predetermined time has elapsed since a forward rotation command was input from the interlocking switch 145. This time is set to be equal to or longer than the time it takes for the starting current required to start rotating the DC motor 12 to converge, and in this embodiment, it is set to be equal to or shorter than one second. Furthermore, the arithmetic processing unit 146 is configured to continue to maintain the stopped state of the DC motor 12 even if the DC motor 12 has stopped as long as the forward rotation switch 141 is pressed and a forward rotation command is input from the interlocking switch 145.

[0013] Next, we will explain the bone W, which is the object to be processed. The bone W is composed of hard cortical bone W1 formed on the surface and soft cancellous bone W2 formed inside the cortical bone W1. Of course, the thickness and hardness of the bone W vary depending on the site and patient, such as bone W where the thickness of the cortical bone W1 is thicker than the length of the tap portion 161 as shown in Figure 3(a) or bone W' where the thickness is thinner than the length of the tap portion 161 as shown in Figure 4(a).

[0014] Hereinafter, the operation of the medical electric tapper 10 when forming a female thread in a bone W that is thicker than the length of the tap portion 161 as shown in FIG. 3(a) will be described. When an operator (not shown) presses the forward rotation switch 141, power is supplied from the battery 13 to the rotation command unit 143 via the forward rotation switch 141. The rotation command unit 143 converts this supplied power, causing the DC motor 12 to start rotating in the forward direction. At this time, the forward rotation switch 141 is pressed, and the DC motor 12 starts rotating in the forward direction. At the same time, the interlock switch 145 outputs a forward rotation command to the arithmetic processing unit 146. After a certain period of time has passed, the arithmetic processing unit 146 receives this forward rotation command and measures the value of the current flowing through the DC motor 12 per unit time and calculates the increase in the current value per unit time. In this way, since the arithmetic processing unit 146 starts monitoring the current value slightly later than 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, the sudden rise in the current value due to the starting current can be ignored, preventing the arithmetic processing unit 146 from measuring the starting current and erroneously stopping the DC motor 12 at the same time as the DC motor 12 starts to rotate.

[0015] When the output shaft 121 of the DC motor 12 and the tap bit 16 connected thereto begin to rotate, the operator inserts the tap portion 161 formed at the tip of the tap bit 16 into a pilot hole formed in the bone W. As a result, the tap bit 16 gradually screws in, forming a female thread on the inner surface of the pilot hole. As the tap bit 16 penetrates the pilot hole, resistance gradually increases, and the current value supplied to the DC motor 12 also gradually increases, as shown between A1 and A4 in FIG. 3(b). During this penetration process, the torque and current value gradually increase due to the cutting torque of the tap portion 161 cutting the cortical bone W1 and the frictional resistance between the cortical bone W1 and the tap portion 161. Therefore, the arithmetic processing unit 146 does not stop the rotation of the DC motor 12 during the penetration process. After that, when the tap portion 161 penetrates to a predetermined depth, the stopper 162 abuts against the periphery of the pilot hole.

[0016] As described above, when the stopper 162 abuts against the surface of the bone W, the stopper 162 prevents the tap bit 16 from penetrating, causing a sudden increase in torque. This causes a sudden increase in the rotational torque of the DC motor 12, which in turn causes a sudden increase in the current value supplied to the DC motor 12, resulting in a sudden increase in the amount of increase in current value per unit time, as shown between A4 and A5 in Figure 3(b). This causes the calculation processing unit 146 to detect that the tap bit 16 has penetrated the bone W by a specified amount and the stopper 162 has abutted against the surface of the bone W, and stops the DC motor 12.

[0017] Next, the operation of the medical electric tapper 10 when forming a female thread in a bone W' that is thinner than the length of the tap portion 161 as shown in FIG. 4(a) will be described. As described above, when the forward rotation switch 141 is pressed, the output shaft 121 of the DC motor 12 and the tap bit 16 connected thereto begin to rotate. The operator then inserts the tap portion 161 into a pilot hole formed in the bone W′. The tap portion 161 then gradually threads into the pilot hole, forming a female thread on the inner circumferential surface of the pilot hole. As the tap portion 161 penetrates the pilot hole, resistance gradually increases. During the female threading process, the tap portion 161 behaves in the same manner as when it drills a female thread into the bone W until the tip of the tap portion 161 penetrates the cortical bone W1 (region 4α in FIG. 4B). Once the tip of the tap portion 161 drills the female thread and penetrates the cancellous bone W2, which is softer than the cortical bone W1 (region 4β in FIG. 4B), the resistance associated with the tap portion 161 becomes almost entirely frictional, and the increase in the current supplied to the DC motor 12 decreases. Thereafter, when the tap portion 161 penetrates to a predetermined depth and the stopper 162 abuts against the periphery of the pilot hole, the stopper 162 prevents the tap bit 16 from penetrating. As a result, the rotational torque of the DC motor 12 increases rapidly, causing the current value supplied to the DC motor 12 to rise sharply, resulting in a rapid increase in the current value per unit time as shown between B4 and B5 in Fig. 4(b). Therefore, similar to the above-described case of drilling an internal thread into the bone W, the calculation processing unit 146 stops the DC motor 12.

[0018] In this way, the medical electric tapper 10 is configured so that the arithmetic processing unit 146 monitors the increase in the power value supplied to the DC motor 12, making it possible to detect when the stopper 162 has come into contact with the bone without being affected by the thickness or hardness of the cortical bone W1. As a result, it becomes possible to drill internal threads into bones with different hardness depending on the individual and the part of the body. Furthermore, because the configuration detects when the stopper 162 has come into contact with the bone from the increase in the current value, it becomes possible to drill an internal thread to the desired depth simply by replacing the tap bit 16.

[0019] Furthermore, because the DC motor 12 stops immediately after the stopper 162 contacts the bone, the reaction torque generated in the direction opposite to the rotational direction of the tap bit 16 and applied to the hand of the operator holding the medical electric tapper 10 is reduced. Furthermore, the medical electric tapper 10 is configured so that the operator grips the cylindrical housing 11, and is therefore lighter than a power tool in which the grip extends radially from the tap bit 16, as described in Patent Document 1. Thus, the medical electric tapper 10 of the present invention is lightweight and generates only a small reaction force when the stopper 162 contacts the bone, resulting in less strain on the operator's hand and allowing the operator (doctor) to use it for extended periods of time during surgery, etc. Furthermore, because the power supply to the DC motor 12 is cut off immediately after the rotation of the tap bit 16 stops, there is also the advantage of not wasting power and improving the battery life of the battery 13.

[0020] A second embodiment in which the tap bit 16 is changed to a tap bit 17 will be described below with reference to Figures 5 and 6. As shown in Figures 5 and 6(a), the second tap bit 17 differs from the first tap bit 16 in that it has a shank 173 between a tap portion 171 and a stopper 172, the shank 173 being thinner than the root diameter of the tap portion 171.

[0021] The operation of the medical electric tapper 10 when forming a female thread in the bone W using the second tap bit 17 having the above configuration will be described. When the entire tap portion 171 penetrates the cortical bone W1, it behaves similarly to the first tap bit 16 (region 5α in FIG. 5B). Once the entire tap portion 171 penetrates the cortical bone W1, the frictional resistance associated with the tap portion 171 no longer changes, and the current value supplied to the DC motor 12 no longer increases (region 5β in FIG. 5B). After that, when the tap portion 171 penetrates to a predetermined depth and the stopper 172 abuts against the periphery of the pilot hole, the stopper 172 prevents the tap portion 171 from penetrating. As a result, the increase in the current value per unit time increases rapidly, as shown between C4 and C5 in FIG. 5B. Therefore, similar to when the first tap bit 16 is used to drill a female thread, the arithmetic processing unit 146 stops the DC motor 12.

[0022] Next, the operation of the medical electric tapper 10 when forming a female thread in the bone W' using the second tap bit 17 will be described. When the tap portion 171 penetrates the cortical bone W1, it behaves similarly to the first tap bit 16 (region 6α in FIG. 6B). When the tip of the tap portion 171 for internal thread machining penetrates the cortical bone W1 and penetrates the cancellous bone W2, the resistance of the tap portion 171 becomes almost entirely frictional, and the increase in the current supplied to the DC motor 12 decreases (region 6β in FIG. 6B). When the tap portion 171 penetrates further and completely penetrates the cancellous bone W2, the frictional resistance of the tap portion 171 no longer changes, and the current supplied to the DC motor 12 no longer increases (region 6γ in FIG. 6B). After that, when the tap portion 171 penetrates to a predetermined depth and the stopper 172 abuts against the periphery of the pilot hole, the stopper 172 prevents the tap bit 17 from penetrating, resulting in a rapid increase in the current per unit time, as shown between D4 and D5 in FIG. 6B. As a result, the arithmetic processing unit 146 stops the DC motor 12.

[0023] The medical electric tapper 10 according to the present invention is not limited to the above-described configuration, and various modifications are possible without departing from the spirit of the invention. For example, the stopper 162 of the tap bit 16 is not limited to a flange shape, and may be a stepped or tapered shape as shown in Figures 7(a) and 7(b). It is preferable that the various dimensions of the tap bit 16 be adjusted appropriately depending on the application. Furthermore, the forward switch 141 and reverse switch 142 may be switches other than push-button switches, such as slide switches or rocker switches. Furthermore, the battery 13 may be either a primary battery or a secondary battery.

[0024] The length of the tap portions 161, 171 varies depending on the length of the screw that will be screwed into the bone W after the internal thread has been formed. Therefore, the length of the tap portions 161, 171 may be longer than the sum of the thicknesses of the cortical bone W1 and the cancellous bone W2. In this case, the tip of the tap portions 161, 171 reaches the cortical bone (not shown) on the back side of the bone W. When the tip of the tap portions 161, 171 reaches the cortical bone on the back side, the current value supplied to the DC motor 12 gradually increases, as in the case when the internal thread is formed on the cortical bone on the front side (see the 6α region in FIGS. 4 to 6(b)). The motor then stops when the stoppers 162, 172 come into contact with the surface of the cortical bone W1.

[0025] The arithmetic processing unit 146 may also be configured to short-circuit the DC motor 12 when it detects that the tap bit 16 has penetrated the bone W by a specified amount and the stopper 162 has come into contact with the surface of the bone W. In this manner, when the arithmetic processing unit 146 is configured to short-circuit the DC motor 12, the DC motor 12 is immediately stopped by the braking action of the back electromotive force generated by the short circuit. Furthermore, in the above embodiment, the medical electric tapper 10 is configured to monitor the current value, but because the current value and rotational torque are proportional to each other in the DC motor 12, there is no problem with a configuration in which a torque sensor is provided on the rotational drive path to monitor the rotational torque. [Explanation of symbols]

[0026] 10...Medical electric tupperware 11... Case 111... Lid member 12...DC motor 121... Output shaft 13...battery 14 ... Control section 141... Forward switch 142... Reverse switch 143... Rotation control unit 144... Rotation control section 145... Interlocking switch 146... Processing unit 15... Gripping chuck 16... Tap Bit 161... Tap section 162... Stopper W… Bone W1…cortical bone W2…cancellous bone

Claims

1. A motor; a power supply for powering the motor; a control unit that connects the power supply and the motor; a housing that can be held by an operator and that can contain the motor and the control unit; a tap bit that rotates when driven by the motor to create an internal thread in the bone, The control unit is configured to cut off the power supply from the power source to the motor when the tap bit penetrates the bone to a predetermined depth.

2. The tap bit has a tap portion for forming an internal thread in a bone, and a stopper that is provided on the proximal side of the tap portion and comes into contact with the surface of the bone when the tap portion penetrates into the bone to a predetermined depth, The medical electric tapper according to claim 1 , wherein the control unit stops the rotation of the motor when it detects that the stopper has come into contact with a bone.

3. The medical electric tapper according to claim 1 or 2, characterized in that the control unit constantly monitors the load current value supplied to the motor, and cuts off the current supplied to the motor when the increase in the load current value per unit time exceeds a predetermined value.

4. 2. The medical electric tapper according to claim 1, wherein the motor is a DC motor.

5. 2. The medical electric tapper according to claim 1, wherein the housing is configured in a cylindrical shape that can be held by an operator.

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