阅读说明：本技术 一种髁导斜度的测量装置 (Condyle guide inclination measuring device ) 是由 许振丰 曹清华 徐玉峰 云峰 于 2020-12-15 设计创作，主要内容包括：本发明涉及一种髁导斜度的测量装置,包括发射器、接收器、处理器、第一测量夹具和第二测量夹具；发射器用于发射测量髁突位置的电磁信号；接收器用于进行位置解算得到位置信息；第一测量夹具用于夹持接收器,提供测量基准点实现左、右侧髁突静态位置测量；第二测量夹具,用于将接收器夹持于下颌运动的随动点上,以测量随动点的静态位置,以及接收器随下颌运动时的动态位姿数据；处理器用于计算左、右侧髁突与随动点的位置差；根据测量的动态位姿数据结合所述位置差数据计算左、右侧髁突的动态轨迹,进而计算髁导斜度。本发明计算的髁导斜度具有很强的实际应用价值,显著提升了电磁面弓面向市场应用的可能性。(The invention relates to a measuring device for condylar guidance inclination, which comprises a transmitter, a receiver, a processor, a first measuring clamp and a second measuring clamp; the emitter is used for emitting an electromagnetic signal for measuring the position of the condylar process; the receiver is used for carrying out position calculation to obtain position information; the first measuring clamp is used for clamping the receiver and providing a measuring reference point to realize the static position measurement of the left and right condyles; the second measuring clamp is used for clamping the receiver on a follow-up point of mandible movement so as to measure the static position of the follow-up point and the dynamic pose data of the receiver when the receiver moves along with the mandible; the processor is used for calculating the position difference between the left and right condyles and the follow-up point; and calculating the dynamic tracks of the left and right condyles according to the measured dynamic pose data and the position difference data, and further calculating the condylar guidance inclination. The condyle guiding inclination calculated by the method has a strong practical application value, and the market application possibility of the electromagnetic face bow is obviously improved.)

1. The measurement device for the condylar guidance inclination is characterized by comprising a transmitter, a receiver, a processor, a first measurement clamp and a second measurement clamp;

the emitter is used for emitting electromagnetic signals for measuring the position of the condylar process;

the receiver is used for receiving the electromagnetic signals and carrying out position calculation to obtain position information;

the first measuring clamp is used for clamping the receiver when the static position measurement of the left and right condyles is carried out, and providing a measuring reference point to realize the static position measurement of the left and right condyles;

the second measuring clamp is used for clamping the receiver on a follow-up point of mandible movement, so that the positions of the receiver and the right and left lateral condyles are kept unchanged when the receiver moves along with the mandible; so that the receiver can measure the static position of the follow-up point and the dynamic pose data when moving along with the lower jaw;

the processor is used for calculating the position difference between the left and right condyles and the follow-up point according to the measured static positions of the left and right condyles and the follow-up point; calculating the dynamic tracks of the left and right condyles according to the measured dynamic pose data and the position difference data; calculating the forward extension condylar guidance inclination according to the motion track of the condylar process in the process of making forward extension or backward retraction of the mandible; and calculating the lateral condylar guidance inclination according to the motion track of the condylar process during the lateral movement of the lower jaw.

2. The device for measuring condylar slope according to claim 1, wherein, during the static position measurement of the left and right condyles using the first measuring jig to clamp the receiver, the head remains stationary, the teeth are kept closed, and the measuring reference point of the first measuring jig is brought into contact with the position of the human face condyles.

3. The device for measuring condylar obliqueness of claim 2, wherein the static position measurement of the left and right condyles is a plurality of measurements, and during the measurement, the first measuring jig is moved including up and down, left and right, and lateral rolling using the reference point as a fulcrum, and a plurality of measurements are obtained in different postures and averaged to obtain the static position of the left and right condyles.

4. The device for measuring condylar guidance slope according to claim 1, wherein said second measuring fixture is a bite fork structure, one end of the bite fork is used for fixing on a tooth, and the other end of the bite fork clamps the receiver; after the occlusion fork is occluded, the receiver and the condyles on the two sides form a rigid structure.

5. The device for measuring condylar guidance slope according to claim 4, wherein, during the static position measurement of the following point using the second measuring fixture holding receiver, the occlusal prongs stick to the lower dentition, are fixedly connected to the central incisor, and the head remains stationary, keeping the teeth closed.

6. The device for measuring condylar obliqueness of claim 1, wherein said processor calculates the difference between the positions of the left and right condyles and the following point from the measured static positions of the left and right condyles and the following point comprises;

calculating the position difference between the right condyle and the follow-up point under the emission coordinate systemDifference in position between the left condyle and the following point

Performing coordinate conversion to obtain a position difference under a receiving coordinate system;

wherein: j is 1 as the right condyle, and j is 2 as the left condyle; and L is a coordinate transformation matrix from a transmitting system to a receiving system.

7. The device for measuring condylar slope of claim 6, wherein the coordinate transformation matrix from the transmit system to the receive system

Wherein the content of the first and second substances,

TC0, TP0, TR0 are heading attitude angle, pitch attitude angle, roll attitude angle of the receiver at the static position of the follower point, respectively.

8. The condylar guidance slope measuring device of claim 1, wherein in the dynamic measurement during the mandibular movement, the mandible moves forwards, backwards, leftwards and rightwards to drive the receiver clamped at the follow-up point to follow up, and the receiver receives the emission signal of the emitter, and the pose data of a series of receivers are obtained through measurement: p4(TX 4)_k、TY4_k、TZ4_k、TC4_k、TP4_k、TR4_k) (k ═ 1,2,3,. N); n is the number of dynamic measurements; TX4_k、TY4_k、TZ4_kRespectively representing the position coordinate three components of the receiver under the emission coordinate system; TC4_k、TP4_k、TR4_kRespectively showing three attitude angles of the receiver, such as heading, pitching and rolling under a transmitting coordinate system.

9. The device for measuring condylar slope of claim 8,

right condylar track:

left condylar track:

wherein, L01_kA coordinate transformation matrix for the receive frame to the transmit frame.

10. The device for measuring condylar slope of claim 9, wherein the coordinate transformation matrix from the receiving system to the transmitting system

Wherein the content of the first and second substances,

Technical Field

The invention belongs to the technical field of medical equipment, and particularly relates to a device for measuring the condylar guidance inclination.

Background

In the field of oral cavity repairing specialties, modelsThe frame is an indispensable step in the diagnosis and treatment process, byThe simulation of the frame can ensure that the coordination of the form and the function is realized after the restoration made on the plaster model is brought into the mouth as much as possible. While in useDuring the frame setting, in order to obtain a simulation result that the error of the actual motion condition of the oral-jaw system of the patient is as small as possible, the position relation between the maxillary dentition and the mandibular joint can be recorded through the facial arch transfer.

In the use process of the face arch, in order to obtain the condylar guidance gradient, the patient needs to do various movements of the mandible to obtain the motion trail of the condylar process. For the motion trail of the condyles, the currently adopted methods are: a) acquiescent two lateral condyles and incisors in the lower jaw form an equilateral triangle with the side length of 95-140 mm; b) the angle between the default occlusion plane and the equilateral triangle is an empirical average (15-25). The original method does not consider the difference of individual patients, and has poor practicability.

Disclosure of Invention

In view of the above analysis, the present invention aims to disclose a device for measuring condylar guide inclination, which can obtain high-precision bilateral condylar motion tracks.

The invention discloses a measuring device for condylar guidance inclination, which comprises a transmitter, a receiver, a processor, a first measuring clamp and a second measuring clamp, wherein the transmitter is used for transmitting a condylar guidance inclination signal to the receiver;

the emitter is used for emitting electromagnetic signals for measuring the position of the condylar process;

the receiver is used for receiving the electromagnetic signals and carrying out position calculation to obtain position information;

the first measuring clamp is used for clamping the receiver when the static position measurement of the left and right condyles is carried out, and providing a measuring reference point to realize the static position measurement of the left and right condyles;

the second measuring clamp is used for clamping the receiver on a follow-up point of mandible movement, so that the positions of the receiver and the right and left lateral condyles are kept unchanged when the receiver moves along with the mandible; so that the receiver can measure the static position of the follow-up point and the dynamic pose data when moving along with the lower jaw;

the processor is used for calculating the position difference between the left and right condyles and the follow-up point according to the measured static positions of the left and right condyles and the follow-up point; calculating the dynamic tracks of the left and right condyles according to the measured dynamic pose data and the position difference data; calculating the forward extension condylar guidance inclination according to the motion track of the condylar process in the process of making forward extension or backward retraction of the mandible; and calculating the lateral condylar guidance inclination according to the motion track of the condylar process during the lateral movement of the lower jaw.

Further, when the first measuring clamp is used for clamping the receiver to perform static position measurement of the left and right condyles, the human head is kept still, and the teeth are kept closed; and enabling the measurement reference point of the first measurement clamp to be in contact with the position of the condyle of the human face.

Further, the static positions of the left and right condyles are measured for a plurality of times, and during measurement, the first measuring jig is moved including up and down, left and right, and lateral rolling with the reference point of measurement as a fulcrum, and a plurality of measurement results are obtained in different postures and averaged to be used as the static positions of the left and right condyles.

Furthermore, the second measuring clamp is of a bite fork structure, one end of the bite fork is used for being fixed on the teeth, and the other end of the bite fork clamps the receiver; after the occlusion fork is occluded, the receiver and the condyles on the two sides form a rigid structure.

Further, when the second measuring clamp is used for clamping the receiver to measure the static position of the follow-up point, the occlusion fork is stuck on the lower tooth column and fixedly connected with the middle incisor, the head of the person keeps still, and the teeth are kept closed.

Further, the process of calculating the position difference between the left and right condyles and the follow-up point by the processor according to the measured static positions of the left and right condyles and the follow-up point comprises the following steps;

in the launching seatCalculating the position difference between the right condyle and the follow-up point under the standard systemDifference in position between the left condyle and the following point

Performing coordinate conversion to obtain a position difference under a receiving coordinate system;

wherein: j is 1 as the right condyle, and j is 2 as the left condyle; and L is a coordinate transformation matrix from a transmitting system to a receiving system.

Further, a coordinate transformation matrix from the transmitting system to the receiving system

L11＝cosTC0*cosTP0

L12＝sinTP0

L13＝sinTC0*(-cosTP0)

L21＝sinTR0*sinTC0-cosTR0*cosTC0*sinTP0

Wherein, L22 is cosTR0 is cosTP 0;

L23＝cosTR0*sinTC0*sinTP0+sinTR0*cosTC0

L31＝sinTR0*cosTC0*sinTP0+cosTR0*sinTC0

L32＝sinTR0*(-cosTP0)

L33＝cosTR0*cosTC0-sinTR0*sinTC0*sinTP0

TC0, TP0, TR0 are heading attitude angle, pitch attitude angle, roll attitude angle of the receiver at the static position of the follower point, respectively.

Further, in the dynamic measurement during the movement of the lower jaw, the lower jaw moves forwards, backwards, leftwards and rightwards to drive the receiver clamped at the follow-up point to follow up, receive the emission signal of the emitter, and obtain a series of pose data of the receiver through measurement: p4(TX 4)_k、TY4_k、TZ4_k、TC4_k、TP4_k、TR4_k) (k ═ 1,2,3,. N); n is the number of dynamic measurements; TX4_k、TY4_k、TZ4_kRespectively representing the position coordinate three components of the receiver under the emission coordinate system; TC4_k、TP4_k、TR4_kRespectively showing three attitude angles of the receiver, such as heading, pitching and rolling under a transmitting coordinate system.

Further, the right condylar track:

left condylar track:

wherein, L01_kA coordinate transformation matrix for the receive frame to the transmit frame.

Further, a coordinate transformation matrix from the receiving system to the transmitting system

L11_k＝cosTC4_k*cosTP4_k

L12_k＝sinTR4_k*sinTC4_k-cosTR4_k*cosTC4_k*sinTP4_k

L13_k＝sinTR4_k*cosTC4_k*sinTP4_k+cosTR4_k*sinTC4_k

L21_k＝sinTP4_k

Wherein, L22_k＝cosTR4_k*cosTP4_k。

L23_k＝sinTR4_k*(-cosTP4_k)

L31_k＝sinTC4_k*(-cosTP4_k)

L32_k＝cosTR4_k*sinTC4_k*sinTP4_k+sinTR4_k*cosTC4_k

L33_k＝cosTR4_k*cosTC4_k-sinTR4_k*sinTC4_k*sinTP4_k

The invention can realize at least one of the following beneficial effects:

the invention does not depend on the equilateral triangle and the included angle between the triangle and the occlusal surface under the assumed condition to determine the motion track of the condylar process, and has the advantages of individuality and practicability. The condylar track is accurate, the calculated condylar guidance inclination has high practical application value, and the market application possibility of the electromagnetic face bow is obviously improved.

Drawings

The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.

FIG. 1 is a diagram showing a relationship of coordinate systems in the present embodiment;

FIG. 2 is a schematic view of a first measuring jig in the present embodiment;

FIG. 3 is a schematic view of a second measuring jig in the present embodiment;

FIG. 4 is a schematic diagram showing the positional relationship between the emitter, the receiver, and the left and right condyles in this embodiment;

FIG. 5 is a comparison of the antero-lateral right condylar track (sagittal plane) in this example;

fig. 6 is a comparison of the antero-lateral left condyle track (sagittal plane) in this example.

Detailed Description

The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and which together with the embodiments of the invention serve to explain the principles of the invention.

The embodiment discloses a measuring device for condylar guidance inclination, which comprises a transmitter, a receiver, a processor, a first measuring clamp and a second measuring clamp;

the emitter is used for emitting electromagnetic signals for measuring the position of the condylar process;

the receiver is used for receiving the electromagnetic signals and carrying out position calculation to obtain position information;

the first measuring clamp is used for clamping the receiver when the static position measurement of the left and right condyles is carried out, and providing a measuring reference point to realize the static position measurement of the left and right condyles;

the second measuring clamp is used for clamping the receiver on a follow-up point of mandible movement, so that the positions of the receiver and the right and left lateral condyles are kept unchanged when the receiver moves along with the mandible; so that the receiver can measure the static position of the follow-up point and the dynamic pose data when moving along with the lower jaw;

the processor is used for calculating the position difference between the left and right condyles and the follow-up point according to the measured static positions of the left and right condyles and the follow-up point; calculating the dynamic tracks of the left and right condyles according to the measured dynamic pose data and the position difference data; calculating the forward extension condylar guidance inclination according to the motion track of the condylar process in the process of making forward extension or backward retraction of the mandible; and calculating the lateral condylar guidance inclination according to the motion track of the condylar process during the lateral movement of the lower jaw.

In the measurement apparatus for condylar guidance inclination of the present embodiment, the following coordinate system used in trajectory measurement is involved, and specifically includes an emission coordinate system using an emitter as an origin and using the front, upper and right sides of the emitter as three axes directions; a receiving coordinate system which takes a follow-up point moving along with the lower jaw as an origin and takes the front, the upper and the right of a receiver clamped at the follow-up point as three axial directions;

as shown in fig. 1, a relationship diagram between a transmitting coordinate system (denoted by T) and a receiving coordinate system, for clarity, a transition coordinate system (denoted by T') is added to the relationship diagram between the coordinate systems;

emission coordinate system definition T: the three axes are defined as X1, Y1, Z1, with the origin at a fixed point or center point of the transmitter used to transmit the measurement signal, with X1 pointing forward (i.e., the direction in which the transmitter transmits the signal), Y1 pointing upward, and Z1 pointing to the right, relative to the transmitter.

The transition coordinate system is defined as T': three axes are defined as X1 ', Y1 ' and Z1 ', the origin is at the following point moving along with the mandible, and the three axes are respectively parallel to three axes of a T emission coordinate system; the follow-up point keeps the positions of the right and left condyles unchanged when moving along with the mandible.

The receive coordinate system is defined as R: three axes are defined as X2, Y2 and Z2, the origin is at the following point so as to be fixed at the following point, and the front, the upper and the right of a receiver for receiving measurement signals are three axes directions; i.e., X2 points to the front of the receiver (i.e., the direction in which the receiver receives signals), Y2 points upward, and Z2 points to the right.

The definition of points in fig. 1, in the emission coordinate system, P1, P2, P3 and P4 mean and are expressed as follows: p1: the right condyle P1(TX 1; TY 1; TZ 1);

p2: the left condyle P2(TX 2; TY 2; TZ 2);

p3: middle incisor position P3(TX 3; TY 3; TZ 3);

p4: the servo point position P4(TX 4; TY 4; TZ 4).

Specifically, as shown in fig. 2, the first measuring jig is configured to clamp the receiver at a receiver clamping position, the measuring reference point of the first measuring jig and the center point of the clamped receiver are in a fixed position relationship, that is, the position of the measuring reference point corresponds to the position of the receiver center point, and the measuring accuracy can be improved by measuring the static positions of the left and right condyles with the measuring reference point of the first measuring jig.

Further, when the first measuring clamp is used for clamping the receiver to perform static position measurement of the left and right condyles, the human head is kept still, and the teeth are kept closed; the first measuring clamp is horizontally placed, the measuring reference point is contacted with the position of the condyle of the human face (the position of the condyle can be determined by touching with hands), and the electromagnetic signal transmitted by the transmitter is received to carry out position calculation to obtain position information.

In order to measure more accurate static positions of the left and right condyles, the present embodiment performs multiple measurements, and during the measurement, the first measurement fixture is moved up and down, left and right, and laterally rolled and the like with the measurement reference point as a fulcrum, so as to obtain multiple measurement results in different postures, and the measurement results are averaged to be used as the static positions of the left and right condyles.

When measuring the right condyle, one set of data can be obtained, which is recorded as:

P1(XP1_i、YP1_i、ZP1_i)(i＝1,2,3,...,n)

wherein: XP1, YP1 and ZP1 respectively represent three components of position coordinates of right condyles in a emission coordinate system in a static state; i 1,2, 3.., n, indicating that n values were measured there.

When measuring the left condyle, one set of data can be obtained, which is recorded as:

P2(XP2_j、YP2_j、ZP2_j)(j＝1,2,3,...,m)

wherein: XP2, YP2 and ZP2 respectively represent three components of the position coordinates of the left condyle under a launching coordinate system in a static state; j-1, 2, 3.., m, indicating that m values were measured there.

Respectively calculating and averaging the measured values of the right and left condyles to obtain the static positions of the right and left condyles in the emission coordinate system:

p1: right condyle process

P2: lateral condyle process

Specifically, as shown in fig. 3, the second measuring clamp is of a bite fork structure, one end of the bite fork is used for being fixed on the tooth, and the other end of the bite fork clamps the receiver; after the occlusion fork is occluded, the receiver and the condyles on the two sides form a rigid structure.

Specifically, when the second measuring fixture is used for clamping the receiver to measure the static position of the follow-up point, the occlusion fork is stuck on the lower tooth column and fixedly connected with the middle incisor, the head of the person keeps still, and the teeth are kept closed. Specifically, the positional relationship of the emitter, the receiver, and the left and right condyles is shown in fig. 4;

measuring an electromagnetic signal transmitted by a transmitter at a static position receiver of the follow-up point to obtain static position information of the follow-up point P4 and attitude information of the receiver;

position information and three attitude angles of the receiver relative to the heading, pitch and roll of the transmitting coordinate are recorded as P4(TX40, TY40, TZ40, TC0, TP0 and TR 0); TX40, TY40 and TZ40 respectively represent three components of coordinates of a following point P4 in a static state and emission coordinate system; TC0, TP0 and TR0 respectively represent three attitude angles of heading, pitch and roll.

In order to determine the dynamic trajectory of the condyles, the processor firstly calculates the position difference between the left and right condyles and the follow-up point according to the measured static positions of the left and right condyles and the follow-up point;

specifically, the process of calculating the position difference between the left and right condyles and the follow-up point by the processor according to the measured static positions of the left and right condyles and the follow-up point includes;

1) the position differences of the condyles P1, P2 and the following point P4 in the emission coordinate system are calculated, respectively.

2) Performing coordinate conversion to obtain the position difference between the left and right condyles and the follow-up point under the receiving coordinate system;

the method specifically comprises the following steps:

(1) coordinate translation is carried out to obtain the position difference of a transition coordinate system T';

is calculated under a transmitting coordinate system T, and because the T 'coordinate is parallel to the T coordinate, under a transition coordinate system T' can be obtained through translation,and is not changed.

(2) Rotating the coordinates to obtain a position difference under a receiving coordinate system R;

wherein: j ═ 1 is the right condyle, and j ═ 2 is the left condyle.

L is a coordinate transformation matrix from a transmitting system to a receiving system, and specifically comprises the following steps:

L11＝cosTC0*cosTP0

L12＝sinTP0

L13＝sinTC0*(-cosTP0)

L21＝sinTR0*sinTC0-cosTR0*cosTC0*sinTP0

L22＝cosR0*cosP0。

L23＝cosTR0*sinTC0*sinTP0+sinTR0*cosTC0

L31＝sinTR0*cosTC0*sinTP0+cosTR0*sinTC0

L32＝sinTR0*(-cosTP0)

L33＝cosTR0*cosTC0-sinTR0*sinTC0*sinTP0

specifically, during dynamic measurement, the processor obtains measurement series pose data of a follow-up point following the movement of the lower jaw; and calculating the dynamic tracks of the left and right condyles according to the pose data and the position difference between the left and right condyles and the follow-up point under the receiving coordinate system.

More specific dynamic measurement procedures are as follows:

1) the lower jaw moves forwards, backwards, leftwards and rightwards to drive a receiver fixed at a follow-up point to follow up, receive a transmitting signal of a transmitter, and obtain a series of measurement numbers of receiver poses by measurement:

P4(TX4_k、TY4_k、TZ4_k、TC4_k、TP4_k、TR4_k) (k ═ 1,2,3,. N); and N is the number of dynamic measurements. TX4_k、TY4_k、TZ4_kRespectively representing the position coordinate three components of the receiver under the emission coordinate system; TC4_k、TP4_k、TR4_kRespectively showing three attitude angles of the receiver, such as heading, pitching and rolling under a transmitting coordinate system.

2) Calculating a position difference under a combined receiving coordinate system R according to the pose data, and calculating a dynamic condylar trajectory;

specifically, the right condylar track:

left condylar track:

wherein L is_o1The method is characterized in that a coordinate transformation matrix from a receiving system to a transmitting system specifically comprises the following steps:

L11_k＝cosTC4_k*cosTP4_k

L12_k＝sinTR4_k*sinTC4_k-cosTR4_k*cosTC4_k*sinTP4_k

L13_k＝sinTR4_k*cosTC4_k*sinTP4_k+cosTR4_k*sinTC4_k

L21_k＝sinTP4_k

L22_k＝cosTR4_k*cosTP4_k。

L23_k＝sinTR4_k*(-cosTP4_k)

L31_k＝sinTC4_k*(-cosTP4_k)

L32_k＝cosTR4_k*sinTC4_k*sinTP4_k+sinTR4_k*cosTC4_k

L33_k＝cosTR4_k*cosTC4_k-sinTR4_k*sinTC4_k*sinTP4_k

calculating the forward extension condylar guidance inclination according to the motion track of the condylar process in the process of making forward extension or backward retraction of the mandible;

in particular, the method comprises the following steps of,

the motion track of the condylar process in the process of the protrusion or the retreat of the mandible is obtained;

calculating the included angle between the motion track of the condylar process and a reference plane (such as a horizontal plane) in the process of making the mandible extend forwards or retreat to obtain the extending condylar guidance inclination;

calculating the lateral condylar guidance inclination according to the motion track of the condylar process of the lower jaw in the lateral moving process;

in particular, the method comprises the following steps of,

according to the obtained motion track of the condyle in the lateral movement process of the lower jaw; in particular to a motion track of the condyle on the non-working side forward, inward and downward;

and calculating the included angle between the forward, inward and downward motion track of the condyle on the non-working side and the sagittal plane to obtain the lateral condyle guidance inclination.

The actual measured left and right condylar tracks of this example are shown in fig. 5-6:

as can be seen from the comparison of the trajectory curves in fig. 5 to 6, a more accurate condylar trajectory is obtained in this embodiment (compared to the trajectory curve of zebris).

Therefore, the motion trail of the condylar process is determined without depending on an equilateral triangle and an included angle between the triangle and the occlusal surface under the assumed condition, and the condylar process has the advantages of individuality and practicability; the condylar track is accurate, the calculated condylar guidance inclination has high practical application value, and the market application possibility of the electromagnetic face bow is obviously improved.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.