Spiral milling end effector for preparing cavity based on planting robot and operation method

Abstract

The spiral milling end effector for preparing the cavity based on the planting robot comprises a planting mobile phone and an end effector used for controlling the planting mobile phone to move, and a milling cutter is installed on the planting mobile phone; a connecting shaft and a connecting rod which are connected with each other are arranged between the end execution device and the planting mobile phone, and the connecting rod is connected with the planting mobile phone; an aligning mechanism used for driving the connecting shaft to rotate is arranged in the tail end executing device, and the connecting shaft is eccentrically arranged on the aligning mechanism; a rotary table for driving the aligning mechanism to rotate is further arranged in the tail end executing device, and the rotating direction of the rotary table is opposite to that of the aligning mechanism; compared with the prior art, the tail end execution device controls the tail end of the planting mobile phone to do spiral-line-shaped movement, the requirement for the overall rigidity of the robot is lowered, the precision problem caused by superposition of movement errors of all joints of the robot is solved, the difficulty and burden of robot tail end track operation are lowered, and the working efficiency is improved. And the stability and efficiency of cavity preparation are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of oral implant robots, and particularly relates to a spiral milling end effector for preparing a cavity based on an implant robot and an operation method. Background Art

[0002] Oral implant technology refers to the technology of preparing a cavity in the human jawbone and implanting an artificial implant in the cavity. After the implant forms osseointegration with the jawbone, a abutment and a denture are installed thereon to help the patient obtain functional restoration such as occlusion and appearance restoration. With decades of development, oral implant has become the most effective method for treating tooth loss. However, the technical threshold of dental implant is relatively high, the surgical operation process is complex, the doctor's learning cycle is long, and the learning cost is relatively high. The doctor's experience and subjective factors have a great influence on the surgical precision and success rate.

[0003] In recent years, modern engineering technologies such as artificial intelligence, CAD / CAM, and 3D printing have been gradually widely applied in the medical field. Surgeons can complete the surgery with the assistance of a surgical guide plate or an implant robot, which can greatly improve the surgical precision, control the error within 0.5 mm, achieve the goal of minimally invasive surgery to the greatest extent, reduce the surgical risk, shorten the surgical time, and realize the standardized operation of implant surgery. Currently, whether it is surgical operation or robot implant hole preparation, a twist drill is used for continuous cutting. During the drilling process, a large amount of heat generated will cause thermal necrosis of bone tissue, which will in turn affect the formation of osseointegration. In order to control the bone wall temperature, twist drills with diameters increasing from small to large need to be replaced during the hole preparation process for step-by-step hole preparation, but the actual effect is not ideal, and cases of implant failure due to thermal burn of bone tissue affecting the formation of osseointegration occur from time to time. On the other hand, when the robot uses a twist drill for step-by-step hole preparation, due to the frequent replacement of milling cutters with different diameters, the tool change operation will cause a significant decrease in the overall hole preparation efficiency, and the repositioning error will also lead to a decrease in the hole preparation precision.

[0004] Currently, the spiral milling hole-making technology in industrial applications cannot be directly used in the field of oral implant. The spiral milling hole-making technology in industrial applications is mostly used for hole-making treatment of difficult-to-machine materials such as composite materials and titanium alloys in the aerospace field. Since the operating space is a relatively large open area, the milling cutter can be clamped and fed along the axial direction, so the spiral milling mechanism is generally relatively simple and easy to implement in design. During oral implant, the operating space in the oral cavity is very narrow, which is completely different from the spiral milling mechanism in industrial applications. The clamping direction of the milling cutter needs to be perpendicular to the axis of the milling cutter, and the spiral motion mechanism can only be arranged outside the oral cavity and far away from the milling cutter.

[0005] Meanwhile, compared with manual operation, the robot has higher accuracy, stability, and repeatability, providing the possibility of preparing oral implant cavities through spiral milling. If the robot directly controls the movement of each joint to drive the implant handpiece to achieve spiral milling interpolation movement for layer-by-layer milling and hole preparation, during the operation process, the robot needs to ensure both the positioning accuracy of implantation and the follow-up accuracy of the patient, as well as the radial revolution movement accuracy and axial feed movement accuracy during layer-by-layer milling. This poses extremely high requirements for the overall stiffness and movement accuracy of the robot. Due to certain errors in the rotational movement of each joint of the robot, it may lead to inaccurate positions and shapes of the cavities prepared by milling, thereby affecting the initial stability and even long-term stability of implantation. Summary of the Invention

[0006] The present invention aims to overcome the above-mentioned defects in the prior art and provides a spiral milling end effector and operation method for preparing cavities based on an implant robot, which can reduce cutting heat and is conducive to the discharge of bone chips.

[0007] To achieve the above-mentioned invention objectives, the present invention adopts the following technical solutions: A spiral milling end effector for preparing cavities based on an implant robot includes an implant handpiece and an end effector device for controlling the movement of the implant handpiece. A milling cutter is installed on the implant handpiece; a centering mechanism for driving the movement of the implant handpiece is provided between the end effector device and the implant handpiece. An indexing table that eccentrically drives the centering mechanism to rotate is also provided inside the end effector device, and the rotation direction of the indexing table is opposite to the rotation direction of the centering mechanism; a sliding assembly for restricting the rotation of the implant handpiece is also provided on the end effector device; the indexing table and the centering mechanism rotate synchronously to make the implant handpiece perform a spiral linear movement.

[0008] As a preferred solution of the present invention, the centering mechanism is installed in the middle of the indexing table, and the centering mechanism includes a meshing worm gear and a worm. A stepping motor for driving the rotation of the worm is provided at the end of the worm, and a connecting shaft is eccentrically arranged on the worm gear.

[0009] As a preferred solution of the present invention, a connecting shaft and a connecting rod for connecting the implant handpiece are installed on the centering mechanism. The connecting shaft is eccentrically arranged on the worm gear, and an eccentricity is formed between the rotation axis of the indexing table and the axis of the connecting shaft.

[0010] As a preferred solution of the present invention, a sensor for observing the position of the worm gear is provided inside the end effector device.

[0011] As a preferred solution of the present invention, the sliding assembly includes a ball joint and a slider connected to each other. A slide rail for restricting the moving direction of the slider is formed on the end effector device, and the slide rail faces the milling cutter.

[0012] As a preferred embodiment of the present invention, the ball joint is connected to the connecting rod, and the ball joint and the implant handpiece are connected to the same end of the connecting rod.

[0013] As a preferred embodiment of the present invention, a clamping bracket for fixedly installing the implant handpiece is provided on the connecting rod.

[0014] As a preferred embodiment of the present invention, the rotation direction of the milling cutter is consistent with the rotation direction of the rotary table.

[0015] An operating method of a spiral milling end effector for preparing a cavity based on a planting robot, including the spiral milling end effector for preparing a cavity based on a planting robot, further including a vision navigation system and a marker fixed on the patient's jawbone, comprising the following steps: Step A: Perform three-dimensional model design according to the patient's oral data, and determine the movement trajectory of the spiral milling cutter according to the patient's three-dimensional model; Step B: Adjust the centering mechanism to the initial position, and install the implant handpiece equipped with the milling cutter on the end effector device; Step C: Fix and install the marker on the patient's jawbone, and set a vision navigation system electrically connected to the end effector device. The end effector device observes the position of the marker and moves the milling cutter to the initial position corresponding to the marker; Step D: The centering mechanism and the rotary table rotate synchronously to drive the milling cutter to perform a spiral movement in the radial direction. When the worm rotates to the designed position, reverse the worm, return the milling cutter to the initial position, and control the end effector device by the planting robot to advance the milling cutter by a feed amount in the axial direction; Step E: Repeat Step D until the depth of the milling cutter reaches the design requirement; Step F: The end effector device retracts to the initial position to complete the hole preparation.

[0016] As a preferred embodiment of the present invention, when the milling cutter is in the initial position, the axis of the milling cutter is concentrically arranged with the axis of the cavity to be prepared.

[0017] Compared with the prior art, the present invention controls the end of the implant handpiece to perform a spiral linear movement through the end effector device, reduces the requirement for the overall stiffness of the robot, solves the accuracy problem caused by the superposition of the motion errors of each joint of the robot, reduces the difficulty and burden of the trajectory calculation at the end of the robot, and improves the stability and efficiency of cavity preparation; Adopting the spiral milling cavity preparation technology reduces the cutting amount, cutting force and heat generated by cutting during cavity preparation. Therefore, less heat is transferred to the bone tissue, and the use of cooling water during the operation is reduced; Moreover, the method of eccentric hole making adopted in this application is beneficial to the discharge of bone chips. The bone chips will not accumulate in the cutting groove of the milling cutter. The heat accumulation around the milling cutter is smaller than that of traditional twist drill drilling, avoiding scratching the surface due to the accumulation of bone chips. The invention uses a small-diameter milling cutter to machine a large-diameter hole, which facilitates the entry of cooling water, improves the cooling effect, and can prepare cavities with different diameters using a single-diameter milling cutter by adjusting the offset amount e of the milling cutter, reducing the repeated positioning error of tool change. Description of the Drawings

[0018] Figure 1 is a schematic structural diagram of the present invention; Figure 2 is the operating principle diagram of the end effector; Figure 3 is the usage state diagram of the present application; Figure 4 is the flow chart of the present application; Reference numerals: end effector 1, implant handpiece 2, milling cutter 21, connecting shaft 3, connecting rod 4, centering mechanism 5, worm 51, worm gear 52, stepping motor 53, rotary table 6, sliding assembly 7, ball hinge 71, slider 72, clamping bracket 8, slide rail 9, marker 10, implant robot 11, visual navigation system 12. Detailed Description of the Invention

[0019] The following will describe in detail the embodiments of the present invention with reference to the drawings.

[0020] As Figures 1 - 4 shown, the spiral milling end effector for preparing a cavity based on an implant robot includes an implant handpiece 2 and an end effector 1 for controlling the movement of the implant handpiece 2. A milling cutter 21 is installed on the implant handpiece 2; a connecting shaft 3 and a connecting rod 4 are connected between the end effector 1 and the implant handpiece 2, and the connecting rod 4 is connected to the implant handpiece 2; a centering mechanism 5 for driving the connecting shaft 3 to rotate is provided in the end effector 1, and the connecting shaft 3 is eccentrically arranged on the centering mechanism 5; a rotary table 6 for driving the centering mechanism 5 to rotate is further provided in the end effector 1, and the rotation direction of the rotary table 6 is opposite to the rotation direction of the centering mechanism 5; a sliding assembly 7 for restricting the rotation of the connecting rod 4 is further provided on the end effector 1; the rotary table 6 and the worm gear 52 rotate synchronously to enable the connecting rod 4 to drive the implant handpiece 2 to perform a spiral linear motion.

[0021] The implant handpiece 2 is fixedly connected to the end effector 1, and the end effector 1 is moved by an implant robot 11. During the movement of the end effector 1, the implant handpiece 2 is synchronously driven to move. A motor for driving the milling cutter 21 to rotate is provided in the implant handpiece 2, so as to perform the operation on the milling cutter 21 under the action of the implant handpiece 2.

[0022] The connecting shaft 3 is rotatably connected to the connecting rod 4. Under the action of the centering mechanism 5, it drives the eccentric rotation of the connecting shaft 3, thereby changing the position of the connecting shaft 3. With the change of the position of the connecting shaft 3, it drives the synchronous movement of the connecting rod 4, thereby realizing the rotation of the milling cutter 21 driven by the connecting rod 4. And the revolution radius of the milling cutter 21 around the rotation center can be adjusted by adjusting the position of the connecting shaft 3 on the centering mechanism 5.

[0023] The centering mechanism 5 is fixedly arranged on the rotary table 6. Under the rotation action of the rotary table 6, it drives the synchronous rotation of the centering mechanism 5, so that the rotation direction of the rotary table 6 is opposite to that of the centering mechanism 5. And under the action of the sliding component 7, the running track of the milling cutter 21 is a spiral line.

[0024] The centering mechanism 5 is installed in the middle of the rotary table 6, and the centering mechanism 5 includes a meshing worm gear 52 and a worm 51. The end of the worm 51 is provided with a stepping motor 53 for driving the rotation of the worm 51, and the connecting shaft 3 is eccentrically arranged on the worm gear 52.

[0025] An eccentric mounting hole for installing the connecting shaft 3 is formed on the worm gear 52. An eccentricity e is formed between the rotation axis of the rotary table 6 and the axis of the connecting shaft 3. The movement track of the milling cutter 21 can be changed by changing the eccentricity e, so as to adjust the diameter of the cavity to be prepared as required.

[0026] A sensor for observing the position of the worm gear 52 is arranged in the end effector 1. The sensor is used to observe the position of the worm gear 52, so as to judge the initial position of the connecting shaft 3. When the connecting shaft 3 is in the initial position, the axis of the connecting shaft 3 and the axis of the rotary table 6 are on the same straight line. The sensor can control the rotation of the worm 51 through the feedback position information, so as to realize the flipping of the worm 51 and drive the worm gear 52 to return to the initial position.

[0027] The sliding component 7 includes a ball hinge 71 and a slider 72 which are connected. A slide rail 9 for restricting the moving direction of the slider 72 is formed on the end effector 1. The slide rail 9 is arranged towards the milling cutter 21. The end of the ball hinge 71 is fixedly connected to the slider 72. The slide rail 9 is a straight structure, and the slider 72 is slidably connected to the slide rail 9. Under the action of the slide rail 9, the moving direction of the slider 72 is guided and limited.

[0028] The end effector 1 is connected to the rotary table 6 through a bearing, so that relative rotation between the end effector 1 and the rotary table 6 can be realized under the action of the rotary table 6. The end effector 1 is always in a relatively static state during the rotation of the rotary table 6 and the centering mechanism 5.

[0029] During the movement of the connecting rod 4, the ball hinge 71 is synchronously driven to move. Thus, under the limitation of the slider 72 on the ball hinge 71, the limitation of the connecting rod 4 in the rotation direction is realized simultaneously. When the slider 72 is sliding, the connecting rod 4 is in a reciprocating swinging state.

[0030] The ball hinge 71 is connected to the connecting rod 4, and the ball hinge 71 and the implant handpiece 2 are connected to the same end of the connecting rod 4. A clamping bracket 8 for fixedly installing the implant handpiece 2 is provided on the connecting rod 4. The clamping bracket 8 is fixedly connected to the connecting rod 4 by bolts, and the clamping bracket 8 is also fixedly connected to the implant handpiece 2 by bolts.

[0031] The rotation direction of the milling cutter 21 is consistent with the rotation direction of the rotary table 6.

[0032] An operating method of a spiral milling end effector for preparing a cavity based on a planting robot, including the spiral milling end effector for preparing a cavity based on a planting robot, further including a visual navigation system 12 and a marker 10 fixed on the patient's jawbone, includes the following steps: Step A: Perform three-dimensional model design according to the patient's oral data, and determine the movement trajectory of the spiral milling cutter according to the patient's three-dimensional model.

[0033] Perform three-dimensional model reconstruction based on the CBCT image of the oral cavity and the data obtained by plaster casting or intraoral scanning, determine the implant plan including the number, position, angle, depth and size of the implants, and determine the movement trajectory and parameters required for the milling cutter 21 on the planting robot 11.

[0034] Step B: Adjust the centering mechanism 5 to the initial position, and install the implant handpiece 2 equipped with the milling cutter 21 on the end effector 1.

[0035] Since the axis of the connecting shaft 3 may not be on the axis of the rotary table 6 due to factors such as collision before power-on, after power-on, the end effector 1 will first reverse the worm 51 to drive the worm gear 52 to return to the initial position according to the position information fed back by the position sensor, perform position initialization operation, and install the implant handpiece 2 equipped with a milling cutter 21 with a suitable diameter on the end effector 1.

[0036] At the same time, before preparing the hole, the operator sets the position, angle and size of the cavity in the graphic interface of the control system of the planting robot 11, and sets the end feed speed, revolution speed, spiral milling revolution radius and feed amount of the milling cutter 21.

[0037] Step C: Fix and install the marker 10 on the patient's jawbone, set the visual navigation system 12 electrically connected to the end effector 1, the end effector 1 observes the position of the marker 10, and moves the milling cutter 21 to the initial position corresponding to the marker 10.

[0038] First, the implant robot 11 obtains the position of the cavity to be prepared based on the marker 10 fixed to the patient's jawbone and the visual navigation system 12, and obtains the corresponding spatial coordinates of the patient's cavity and the spatial coordinates of the milling cutter 21 in real time through the marker 10, the visual navigation system 12, and the implant handpiece 2. By the difference between the two spatial coordinates, the implant robot 11 is guided so that the axis of the milling cutter 21 on the end effector 1 and the axis of the implant cavity pre-designed are on the same straight line, making the end of the milling cutter reach the initial position, and controlling the axial movement of the implant handpiece 2 so that the end of the milling cutter 21 approaches the required cavity.

[0039] Step D: The centering mechanism 5 and the rotary table 6 rotate synchronously to drive the milling cutter 21 to perform a helical movement in the radial direction. After the worm 51 rotates to the designed position, the worm 51 is reversed to return the milling cutter 21 to the initial position, and the end effector 1 is controlled by the implant robot 11 to advance the milling cutter 21 by a feed amount in the axial direction.

[0040] Under the action of the centering mechanism 5 and the rotary table 6, the helical movement of the milling cutter 21 on the same plane is realized. At the same time, in cooperation with the rotation of the milling cutter 21 itself, the milling cutter 21 is milled along the helical line direction, and under the action of the implant robot 11, the feed of the milling cutter 21 on different planes is realized.

[0041] After the implant robot 11 drives the end effector 1 to reach the predetermined position, the worm 51 rotates to drive the worm gear 52 to rotate, and the required revolution radius of the implant handpiece 2 is adjusted by setting the eccentricity e. At the same time, in cooperation with the uniform rotation of the rotary table 6 to drive the implant handpiece 2 to perform a helical movement. When the worm 51 rotates a certain number of turns, at this time, the milling cutter 21 moves along the helical line direction to the required position. After the worm 51 reaches the specified number of turns, it is reversed until the implant handpiece 2 and the milling cutter 21 return to the initial position consistent with the cavity axis. At this time, the milling cutter 21 returns to the initial position. The implant robot 11 controls the end effector 1 to advance the milling cutter 21 by a feed amount in the axial direction, and moves the end of the milling cutter 21 to the next required milling plane.

[0042] Step E: Repeat Step D until the depth of the milling cutter 21 reaches the design requirements. Step F: The end effector 1 retracts to the initial position to complete the hole preparation.

[0043] When the milling cutter 21 is in the initial position, the axis of the milling cutter 21 is concentrically arranged with the axis of the cavity to be prepared.

[0044] In this solution, the worm 51 drives the worm gear 52 to rotate to adjust the distance between the axis of the rotary table 6 and the axis of the connecting rod shaft 3, thereby adjusting the eccentricity e. The eccentricity e is the distance between the axis of the rotary table 6 and the axis of the connecting rod shaft 3. The rotation of the rotary table 6 drives the movement of the connecting rod 4 and the slider 72, so that the planting handpiece 2 connected to the end of the connecting rod 4 moves in a spiral shape. When the centering mechanism 5 does not move, during the rotation of the rotary table 6, the movement trajectory of the milling cutter 21 at the end of the planting handpiece 2 is a circular path.

[0045] When the rotary table 6 rotates and the centering mechanism 5 does not rotate, the slider 72 moves, and the end of the planting handpiece 2 will perform a circular motion with the eccentricity e as the radius of revolution at this time. When the rotary table 6 rotates and the centering mechanism 5 rotates, the centering mechanism 5 will drive the worm gear 52 to rotate, the slider 72 moves along the slide rail 8, and the milling cutter 21 at the end of the planting handpiece 2 feeds in a spiral shape along the direction of revolution. At the same time, the milling cutter 21 rotates on its own axis, and the axial feeding movement is completed by the planting robot 11.

[0046] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0047] Although terms such as end effector 1, planting handpiece 2, milling cutter 21, connecting shaft 3, connecting rod 4, centering mechanism 5, worm 51, worm gear 52, stepper motor 53, rotary table 6, sliding assembly 7, ball hinge 71, slider 72, clamping bracket 8, slide rail 9, marker 10, planting robot 11, vision navigation system 12, etc. are used more frequently in this article, the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. The spiral milling end effector for preparing a cavity based on a planting robot, comprising a planting handpiece (2) and an end effector device (1) for controlling the movement of the planting handpiece (2), wherein a milling cutter (21) is mounted on the planting handpiece (2); characterized in that, A centering mechanism (5) for driving the planting handpiece (2) to move is provided between the end effector (1) and the planting handpiece (2). A rotary table (6) for eccentrically driving the centering mechanism (5) to rotate is further provided inside the end effector (1). The rotation direction of the rotary table (6) is opposite to that of the centering mechanism (5). A sliding assembly (7) for restricting the rotation of the planting handpiece (2) is further provided on the end effector (1). The rotary table (6) and the centering mechanism (5) rotate synchronously to make the planting handpiece (2) perform a spiral motion.

2. The helical milling end effector for preparing cavity based on the planting robot according to claim 1, characterized in that, The centering mechanism (5) is installed in the middle of the rotary table (6), and the centering mechanism (5) includes a worm gear (52) and a worm (51) that mesh with each other. A stepping motor (53) for driving the worm (51) to rotate is provided at the end of the worm (51).

3. The spiral milling end effector for preparing a cavity based on a planting robot according to claim 1, wherein A connecting shaft (3) and a connecting rod (4) for connecting the planting handpiece (2) are installed on the centering mechanism (5). The connecting shaft (3) is eccentrically arranged on the worm gear (52), and an eccentricity is formed between the rotation axis of the rotary table (6) and the axis of the connecting shaft (3).

4. The spiral milling end effector for preparing cavity based on the planting robot according to claim 1, characterized in that, A sensor for observing the position of the worm gear (52) is provided inside the end effector (1).

5. The spiral milling end effector for preparing cavity based on the planting robot according to claim 1, characterized in that, The sliding assembly (7) includes a ball joint (71) and a slider (72) connected to each other. A slide rail (9) for restricting the moving direction of the slider (72) is formed on the end effector (1), and the slide rail (9) is arranged towards the milling cutter (21).

6. The helical milling end effector for preparing a cavity based on a planting robot according to claim 5, characterized in that, The ball joint (71) is connected to the connecting rod (4), and the ball joint (71) and the planting handpiece (2) are connected to the same end of the connecting rod (4).

7. The spiral milling end effector for preparing a cavity based on a planting robot according to claim 6, wherein, A clamping bracket (8) for fixedly installing the planting handpiece (2) is provided on the connecting rod (4).

8. The spiral milling end effector for preparing cavity based on the planting robot according to claim 1, characterized in that, The rotation direction of the milling cutter (21) is consistent with the rotation direction of the rotary table (6).

9. The operating method of the spiral milling end effector for preparing cavity based on a planting robot, characterized in that, It includes a spiral milling end effector for preparing a cavity based on a planting robot according to any one of claims 1-8, and further includes a visual navigation system (12) and a marker (10) fixed on the patient's jaw bone, including the following steps: Step A: Perform three-dimensional model design according to the patient's oral data, and determine the motion trajectory of the spiral milling according to the patient's three-dimensional model. Step B: Adjust the centering mechanism (5) to the initial position, and install the planting handpiece (2) equipped with the milling cutter (21) on the end effector (1). Step C: Fix and install the marker (10) on the patient's jaw bone, and set a visual navigation system (12) electrically connected to the end effector (1). The end effector (1) observes the position of the marker (10), and moves the milling cutter (21) to the initial position corresponding to the marker (10). Step D: The centering mechanism (5) and the rotary table (6) rotate synchronously to drive the milling cutter (21) to perform a spiral motion in the radial direction. When the worm (51) rotates to the designed position, reverse the worm (51), return the milling cutter (21) to the initial position, and control the end effector (1) by the planting robot (11) to move the milling cutter (21) forward by a feed amount in the axial direction. Step E: Repeat Step D until the depth of the milling cutter (21) reaches the designed requirement. Step F: The end effector (1) retracts to the initial position to complete the preparation of the hole.

10. The operating method of the spiral milling end effector for preparing cavity based on the planting robot according to claim 9, characterized in that, When the milling cutter (21) is in the initial position, the axis of the milling cutter (21) is concentric with the axis of the cavity of the hole to be prepared.

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