JP2020031735A - Medical device - Google Patents

Abstract

To provide a medical device with improved starting performance of a motor.SOLUTION: A medical device includes a handpiece for holding a tool rotatably, a motor for rotatably driving the tool, a control unit for controlling the motor, and an operation unit for setting the number of rotations of the motor in operation. The motor includes a rotor and a stator having a coil. When a driving voltage corresponding to the set number of rotations of the motor is lower than a reference starting voltage, which is a voltage required for starting the motor, the control unit has only to start the motor by changing the driving voltage when starting the motor to the reference starting voltage.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a medical device for cutting teeth and alveolar bone in dental treatment.

Conventionally, a handpiece that rotatably holds various tools such as a cutting tool, a tap for forming a screw groove, an implant driver, and the like in a head portion, a motor serving as a drive source for rotating these tools, and controlling the motor There is a medical device having a control unit that performs the control.
Such a medical device forms a holding hole for holding an implant in an alveolar bone forming a jaw region of a patient and forms a screw groove for screwing the implant in the holding hole in an implant operation in dental treatment. It is used to fix the implant by screwing it to the holding hole with a specified tightening torque.

Some of such medical devices use a sensorless motor that detects the rotational angle position of a rotor and performs drive control without using a sensor such as a Hall element, as disclosed in Patent Document 1.
The sensorless motor detects an induced voltage generated in each coil (winding) constituting a stator (stator), detects a rotation angle position of the rotor with respect to the stator based on the detected voltage, and uses an inverter circuit to detect a rotation angle position of the rotor by an inverter circuit. Is supplied to each coil to rotate the rotor.

JP-A-2002-253576

In the motor disclosed in Patent Literature 1, when the rotor is rotating, an induced voltage that can detect the rotational angle position of the rotor is generated in the coil.
However, when the rotor is stopped, no induced voltage is generated in the coil that can detect the rotational angle position of the rotor. For this reason, when starting the motor, it is necessary to fix the position of the rotor by applying a current to the coil by applying a direct current, and then forcibly change the coil phase to rotate the rotor.
In particular, when driving is started with the motor set to operate at low rotation, the induced voltage of the coil generated during driving is small, and it is difficult to detect the rotational angle position of the rotor. That is, when the motor is set to operate at a low rotation and the operation is started, there is a problem that the startability of the motor is not stable.

  The present invention has been made to solve the above-described problem, and has as its object to provide a medical device with improved motor startability.

  In order to solve the problem, in a medical device, a handpiece that rotatably holds a tool, a motor that rotationally drives the tool, a control unit that controls the motor, and a rotation speed or rotation speed during operation of the motor. The motor includes a rotor and a stator having a coil, and the control unit controls a driving voltage corresponding to the set rotation speed of the motor to be a voltage necessary to start the motor. If the starting voltage is lower than the starting reference voltage, the driving voltage for starting the motor may be changed to the starting reference voltage to start the motor.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the medical device using the motor which the starting property improved.

Schematic diagram showing the connection between the handpiece, motor, and main body that constitute the medical device Circuit diagram of medical device Block diagram showing a medical device Flow chart showing control steps when starting the motor (A) A graph of the voltage value with respect to the number of rotations of the motor showing the state of S4 in the flowchart of FIG. 4 (b) A graph of the voltage value with respect to the rotation number of the motor showing the state of S6 of the flowchart of FIG.

(Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Referring to FIG. 1, the medical device M includes a dental handpiece 100 (hereinafter, handpiece 100), a motor 200, and a main body 300.
The handpiece 100 holds various rotary tools 102 (hereinafter, tools 102) on a head unit 101 located on the distal end side. The tool 102 is, for example, a cutting tool for cutting teeth, a tap for forming a screw groove in an opening formed in the alveolar bone, or an implant driver for screwing an implant into the opening with a specified torque.
A motor 200 described later is connected to the rear end of the handpiece 100. The user holds the handpiece 100 configured as described above by hand and treats the affected part.

The motor 200 has its output shaft connected to the rear end of the handpiece 100, and is driven and controlled by a control unit 301 described later. In the present embodiment, motor 200 has a stator (not shown) having three-phase coils 212 (212u, 212v, 212w) composed of U-phase, V-phase, and W-phase, and a magnetic field generated by each coil 212 acts. A three-phase brushless motor provided with a rotor (not shown) having a magnet that rotates together with the output shaft is used.
The motor 200 configured as described above serves as a drive source that rotationally drives the tool 102 held by the head unit 101 using the rotation torque output from the output shaft.

2 and 3, the main body 300 includes a control unit 301, a storage unit 302, a driving unit 303, an operation unit 304, a display unit 305, a motor current detection unit 306, and a rotation speed detection unit 307. , A load torque detecting unit 308, and a power supply unit 309. A foot pedal 310 is connected to the main body 300. The output of the foot pedal 310 is input to the control unit 301.
The drive system of motor 200 in the present embodiment is a PWM (Pulse Width Modulation) drive system.

Next, each functional unit will be described.
The control unit 301 obtains power from the power supply unit 309 and drives the drive unit 305 based on inputs from the operation unit 303, the foot pedal 310, and each detection unit, and a control algorithm stored in the storage unit 302. , And controls the operation of the motor 200.
That is, the control unit 301 stores the rotation speed Rr of the motor 200, the load torque Tr acting on the motor 200 during use, the detected value of the motor current Im (Iu, Iv, Tw) flowing through the motor 200, and the storage unit 302. The motor 200 is controlled based on the stored driving conditions.
In other words, the control unit 301 controls the driving unit 303 to generate the PWM signal by controlling the motor 200 such that the rotation speed Rr and the motor current Im are set by the user. The control unit 301 also controls the rotation directions of the forward rotation and the reverse rotation of the motor 200.

  The storage unit 302 is connected to the control unit 301. The storage unit 302 stores various programs for the control unit 301 to control the motor 200 and driving conditions necessary for controlling the driving of the motor 200. These driving conditions can be set to arbitrary values by the user in consideration of the treatment content, the type of tool, and the like. Further, the storage unit 302 stores data detected by various detection units provided in the main body 300 and input data from the operation unit 304.

The motor current detection unit 306 is connected to a circuit that connects the drive unit 303 and each of the three-phase coils 212 of the motor 200, and detects the currents Iu, Iv, and Iw flowing through the U-phase, V-phase, and W-phase, respectively. The motor current detection unit 306 includes a current detection resistor, and converts the detected currents Iu, Iv, Iw into voltages Vu, Vv, Vw. The voltages Vu, Vv, Vw are U-phase, V-phase, and W-phase terminal voltages, respectively. Then, the values of the detected voltages Vu, Vv, and Vw are input to the control unit 301, the rotation speed detection unit 307, and the load torque detection unit 308.

The rotation speed detection unit 307 estimates an induced voltage generated in the coils 212 of each phase of the motor 200 from the voltage value obtained by the motor current detection unit 306. Then, the rotational speed Rr of the motor 200 is obtained from the induced voltage. Note that the portion for obtaining the induced voltage may be provided independently of the rotation speed detection unit 307, or may be obtained by the control unit 301. Further, the number of rotations of the motor is obtained 301 by the control unit 301 based on the rotation speed Rr.
The load torque detection unit 308 obtains the load torque Tr from the voltage value obtained by the motor current detection unit 306, utilizing the fact that the motor current Im and the load torque Tr are in a proportional relationship.
The detection values of the rotation speed detection unit 307 and the load torque detection unit 308 described above are input to the control unit 301.

The operation unit 304 includes a main power switch and setting / selection buttons.
The main power switch is a switch for turning on or off the power of the main body 300. The setting / selection button is a button for setting driving conditions necessary for controlling the operation mode, rotation speed, driving torque, and the like of the motor 200. A user can operate a setting / selection button provided on the operation unit 304 to input a setting of a use condition of the operation of the motor 200. The foot pedal 310 operates and stops the motor 200 when the user operates the foot with the foot.

The driving unit 303 includes an inverter circuit configured by six FETs (Field Effect Transistors). The FETs are connected to the phases of the corresponding coils 212 of the motor 200, respectively.
In this inverter circuit, based on the PWM signal from the PWM signal generation circuit 301a provided in the control unit 301, each FET cyclically controls ON (ON) / OFF (OFF) in synchronization with the rotation angle position of the rotor. . That is, the control unit 301 controls the six FETs to perform ON / OFF control appropriately, thereby energizing the three-phase coil 212 in six patterns. As a result, the drive voltage Vd is applied to the motor 200.
As described above, the drive voltage Vd is cyclically applied to each phase of the coil 212 to generate a current, and a magnetic field is generated. The action of the magnetic field causes the rotor 201 of the motor 200 to rotate.

The PWM signal generation circuit 301a generates a PWM signal based on a detection signal of the rotor position detection circuit 301b provided in the control unit 301.
The rotor position detection circuit 301b detects the rotation angle position of the rotor by using the value of the induced voltage generated when the rotor rotates and the coil phase is switched (a so-called sensorless circuit that does not use a sensor such as a Hall element). Is used.

  The sensorless rotor position detection circuit 301b determines the terminal voltage of the non-energized phase among the U-phase, V-phase, and W-phase based on the induced voltage generated in the coil, and sets the medium potential of the applied drive voltage Vd. By detecting a point (zero cross point) where (1/2) is reached, the rotational angle position of the rotor 201 with respect to the stator 202 is detected. Note that the value induced by the rotation speed detection unit 307 is used as the induced voltage.

Here, the driving torque and the rotation speed Rr of the motor 200 are determined by a duty ratio which is a ratio of the ON signal to one cycle of the PWM signal. That is, if the duty ratio is increased by increasing the ON time of the FET, the effective value of the drive voltage Vd applied to the motor 200 increases. That is, the drive voltage Vd increases. Thereby, the rotation speed Rr can be increased.
Further, when the duty ratio is reduced by shortening the ON time of the FET, the effective value of the drive voltage Vd applied to the motor 200 is reduced, the drive torque is reduced, and the rotation speed Rr can be reduced.

When the load torque Tr applied to the cutting tool increases, the rotation speed Rr of the motor 200 decreases. In this case, too, the duty ratio of the PWM signal is increased, and the effective value of the drive voltage Vd is increased. Then, as the motor current Im of the motor 200 increases, the driving torque increases, and as a result, the rotation speed Rr can be increased (maintained).
As described above, the control unit 301 controls the rotation speed Rr and the driving torque of the motor 200 by controlling the duty ratio of the PWM signal.

The display unit 305 displays various driving conditions stored in the storage unit 302, and also displays the rotation speed Rr of the motor 200 in use, the set driving torque, and the like.
The foot pedal 310 controls ON / OFF of the rotation operation of the motor 200. The control unit 301 detects the presence or absence of a signal from the foot pedal 310, and if there is a signal, drives the motor 200 according to the drive conditions.
The power supply unit 309 is a converter that rectifies and transforms an AC voltage from an external AC power supply 400 and applies a desired DC voltage to the control unit 301 and the drive unit 303.

Next, the control at the time of starting the motor according to the present embodiment will be described based on the flowchart shown in FIG. 4 and the graph shown in FIG.
The flowchart shown in FIG. 4 is an operation control step at the time of starting the motor 200 when starting use of the medical apparatus M. That is, this is a control step when operating the foot pedal 310 to rotate the motor 200.
The graph shown in FIG. 5A is a graph of the number of rotations of the motor and the voltage value showing the state of S4 in the flowchart of FIG. The graph shown in FIG. 5B is a graph of the rotation speed of the motor and the voltage value showing the state of S6 in the flowchart of FIG.

First, when the user turns on the main power of the main body 300, performs setting input related to the operation of the medical device M from the operation unit 304, and starts the operation of the motor 200 for performing a treatment operation, the control unit 301 executes a control step. Is shifted to step S1.
The setting input performed before starting the operation of the motor 200 relates to, for example, the operation speed, the driving torque, and the operation mode of the motor 200. This operation mode includes, for example, an operation mode for forming a screw groove in the alveolar bone used for implant treatment, and a mode in which the implant is tightened to the opening of the alveolar bone having the screw groove with a specified torque.
The operation of the motor 200 is switched on and started when the user steps on the foot pedal 310, for example.

  In step S1, the control unit 301 controls the driving unit 303 to supply a current to the coil 212 for a very short time. As a result, a constant magnetic field is formed in the coil, and the rotor 201 receives the influence of the magnetic field, and the position of the rotor 201 is fixed (DC conduction in open loop control). Then, when the position of the rotor 201 is fixed with respect to the stator 202, the control step of the motor 200 shifts to step S2. In the present embodiment, the process shifts to S2 via S1, but S2 may be performed without performing the process of S1 after the operation starts.

  In step S2, the control unit 301 controls the driving unit 303 to energize the coil 212 in six patterns and detect magnetic saturation. Then, the control unit 301 estimates the initial position of the rotor 201 with respect to the stator 202 based on the detected position of the magnetic saturation, and shifts the control step of the motor 200 to step S3.

In step S3, the control unit 301 determines whether the drive voltage Vd of the motor 200 corresponding to the rotation speed of the motor 200 set and input from the operation unit 304 is smaller than a motor start reference voltage (hereinafter, start reference voltage Va). Judge.
When the drive voltage Vd is smaller than the start reference voltage Va, the control unit 301 proceeds to step S4. When the drive voltage Vd is equal to or larger than the start reference voltage Va, the control unit 301 proceeds to step S7.

Here, the drive voltage Vd is a voltage applied to the coil 212 for driving the motor 200 to rotate. As the value of the drive voltage Vd increases, the rotation speed of the motor 200 increases.
For example, assuming that the drive voltage Vd1 when the set rotation speed is 100 rpm, the drive voltage Vd2 when the set rotation speed is 1000 rpm, and the drive voltage Vd3 when the set rotation speed is 10,000 rpm, the relationship is Vd1 <Vd2 <Vd3.

The start reference voltage Va is a voltage necessary for stably starting the motor 200 from a stopped state. That is, the starting reference voltage Va is a voltage necessary for stably starting the motor 200. The start reference voltage Va differs depending on the characteristics of the motor 200, but the drive voltage Vd at low rotation may be lower than the start reference voltage Va.
In particular, when performing various treatment operations using one motor as in the medical device M of the present embodiment, the rotation speed of the motor has a range from low rotation to medium-high rotation depending on the situation.

For example, in the case of the medical device M, when the motor 200 is operated at a medium to high rotation speed, it is mainly used to cut a patient's teeth or cut an alveolar bone to form a holding hole for holding an implant. Used for
When the motor 200 is operated at a low rotation speed, a screw groove for screw-fixing the implant is formed in the holding hole, or the implant is screwed and fixed to the holding hole with a specified torque. Can be The treatment operation performed by operating the motor 200 at a low rotation requires a particularly delicate operation.

Although it depends on the characteristics of the medical device M, generally, the low rotation is about 100 to 500 rpm, and the medium to high rotation is about 500 to 20,000 rpm. In the case of a low rotation speed, there is a rotation region where the drive voltage Vd is lower than the starting reference voltage Va.
For example, when the drive voltage corresponding to the start reference voltage Va is a voltage when the rotation speed is 300 rpm, and when the set rotation speed set at the start of the operation is less than 300 rpm, the motor 200 may not be able to start stably. There is. That is, there is a possibility that the user's delicate work may be hindered.

Next, in step S4, the control unit 301 controls the driving unit 303 to apply the activation reference voltage Va to the coil 212 to forcibly change the phase of the coil 212. As a result, the rotor 201 rotates under the influence of the change in the phase of the coil 212. After performing the processing in step S4, the control unit 301 proceeds to step S5.
In step S4, since the motor 200 cannot be stably started with the drive voltage Vd corresponding to the rotation speed set by the operation unit 304, the start reference voltage which is a voltage higher than the drive voltage Vd of the set rotation speed This is a step of driving the motor 200 by setting the voltage at the start of driving to Va.

  In other words, in step S4, if the drive voltage Vd for maintaining the set number of revolutions is too low to start the motor 200 stably, the voltage at the start of startup is set to a voltage higher than the drive voltage Vd. This is a step of setting the starting reference voltage Va to start driving the motor 200.

Next, in step S5, the control unit 301 determines whether the rotor position detection circuit 301b has detected the rotational angle position of the rotor 201 with respect to the stator 202.
When the rotor position detection circuit 301b detects the rotation angle position of the rotor 201 with respect to the stator 202, the control unit 301 proceeds to step S6. When the rotor position detection circuit 301b does not detect the rotation angle position of the rotor 201 with respect to the stator 202, the control unit 301 repeats the process of step S5.

Next, in step S6, the control unit 301 changes the drive voltage Vd so that the rotation speed of the motor 200 is set at the time of startup.
More specifically, the control unit 303 reduces the voltage from the state of the start reference voltage Va, which is a voltage higher than the drive voltage Vd of the number of revolutions set for stably starting the motor 200, thereby setting the voltage. The drive voltage is changed to the drive voltage Vd at the set rotation speed.
When the above processing ends, the control means 301 proceeds to step S9.
The above is the flow of the processing in steps S4 to S6.

In step S3, the control unit 301 shifts the control step of the motor 200 to step S7 when the drive voltage Vd is equal to or higher than the startup reference voltage Va.
In step S7, the control unit 301 controls the driving unit 303 to apply the driving voltage Vd corresponding to the rotation speed set to the coil 212, and forcibly changes the phase of the coil 212. As a result, the rotor 201 rotates under the influence of the change in the phase of the coil 212. After performing the process in step S7, the control unit 301 proceeds to step S8.

Next, in step S8, the control unit 301 determines whether the rotor position detection circuit 301b has detected the rotational angle position of the rotor 201 with respect to the stator 202.
When the rotor position detection circuit 301b detects the rotation angle position of the rotor 201 with respect to the stator 202, the control unit 301 proceeds to step S9. When the rotor position detection circuit 301b does not detect the rotation angle position of the rotor 201 with respect to the stator 202, the control unit 301 repeats the process of step S7.
Note that the control unit 301 controls the driving unit 303 to control the rotation speed Rr and the driving torque of the motor 200 based on the detection value of the rotor position detection circuit 301b after step S5 or step S8.

Next, in step S9, the control unit 301 determines whether the setting of the rotation speed of the motor 200 has been changed. Specifically, it is determined whether or not a change in the setting of the rotation speed of the motor 200 has been input from the operation unit 304 to the control unit 301.
The control unit 301 proceeds to step S10 when the above setting change is input, and proceeds to step S11 when there is no input.

Next, in step S10, the control unit 301 controls the drive unit 303 to change the drive voltage Vd to the drive voltage Vd corresponding to the rotation speed of the motor 200 to which the setting change is input from the operation unit 304. And the process proceeds to step S11.
In step S11, the control unit 301 determines whether there is an input for stopping the operation of the motor 200.
Specifically, it is determined whether or not the switch of the foot pedal 310 has been turned off. If there is an input to stop motor 200, control unit 301 stops motor 200 and ends the process. If there is no input to stop motor 200, control unit 301 proceeds to step S9.

  As described above, in the medical device M, the control unit 301 determines that the drive voltage Vd corresponding to the set rotation speed of the motor 200 is smaller than the activation reference voltage Va that is a voltage necessary to activate the motor 200. Then, the drive voltage Vd for starting the motor 200 is changed to the start reference voltage Va, and the motor 200 is started. By controlling the motor 200 in this manner, the motor 200 can be stably started even at a low rotation speed where the drive voltage Vd is low.

In particular, in the sensorless motor 200, even when the drive voltage Vd is low and the rotation is low, the motor 200 can be stably started. Therefore, even when the work is performed by rotating the tool 102 at a low rotation, the operation is started from the operation start. A series of movements can be performed stably.
The operation performed by rotating the tool 102 at a low rotation includes, for example, an operation of forming a screw groove in a hole formed in the alveolar bone and an operation of screwing an implant into the hole formed with the screw groove with a specified torque. is there.
These operations are performed in a rotation range where the number of rotations of the motor 200 is low. According to the present invention, the motor 200 can be started stably in the process from the start of the motor 200 to the operation. Therefore, the user does not easily feel a sense of discomfort at the time of starting the motor, and work is easy.

  Further, after the motor 201 is started, the control unit 301 changes the drive voltage Vd to a drive voltage Va corresponding to the set rotation speed of the motor 200 from the start reference voltage Va. By controlling the motor 201 in this manner, the number of revolutions immediately after the start is set by the user, and the workability from the start of the motor 201 to the affected part is improved.

  Further, when changing the drive voltage from the start reference voltage Va to the drive voltage Vd corresponding to the set rotation speed of the motor 200, the control unit 301 changes the drive voltage stepwise or linearly. By controlling the motor 201 in this way, the user can reduce the sense of discomfort from the start of the motor 201 until the rotation speed is set.

  As described above, in the present embodiment, the case where the operation state of the motor set by the user is the number of rotations has been described as an example, but the rotation speed may be set. In the flowchart shown in FIG. 4, the present invention has the same effect even if the description of “rotation speed” is replaced with “rotation speed”.

M medical device 100 dental handpiece (handpiece)
101 Head unit 102 Tool 200 Motor 201 Rotor 202 Stator 212 Coil 212u U-phase coil 212v V-phase coil 212w W-phase coil 300 Main unit 301 Control unit 301a PWM signal generation circuit 301b Rotor position detection circuit 302 Storage unit 303 Drive unit 304 Operation unit 305 Display unit 306 Motor current detection unit 307 Rotation speed detection unit 308 Load torque detection unit 309 Power supply unit 310 Foot pedal 400 AC power supply

Claims (6)

A handpiece that holds the tool rotatably,
A motor that rotationally drives the tool,
A control unit for controlling the motor,
An operation unit for setting a rotation speed or a rotation speed during operation of the motor;
Has,
The motor includes a rotor and a stator having a coil,
When the drive voltage corresponding to the set rotation speed or rotation speed of the motor is smaller than a start reference voltage that is a voltage necessary to start the motor, the control unit drives the motor when starting the motor. A medical device wherein the motor is started by changing a voltage to a start reference voltage.   2. The control unit according to claim 1, wherein, after the motor is started, the control unit changes the drive voltage to a drive voltage corresponding to a set rotation speed or rotation speed of the motor from a start reference voltage. 3. Medical device.   The control unit changes the drive voltage stepwise or linearly when changing the drive voltage from a start reference voltage to a drive voltage corresponding to the set rotation speed or rotation speed of the motor. A medical device according to claim 1. The coil comprises three phase coils,
The control unit includes a rotor position detection circuit that detects a rotation angle position of the rotor by using a value of an induced voltage generated when the rotor rotates and the phase of the coil is switched,
The rotor position detection circuit detects a position where a terminal voltage of a non-energized phase among the three phases becomes a middle potential of a driving voltage to be applied, based on an induced voltage generated in each phase of the coil. The medical device according to claim 1, wherein a rotation angle position of the rotor with respect to the stator is detected.   The medical device according to claim 1, wherein the tool is a tap that forms a screw groove, and drives the motor to form the screw groove in the alveolar bone.   The medical device according to claim 1, wherein the tool is a driver, and the motor is driven to attach the implant to an opening having a screw groove that opens into the alveolar bone.

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