阅读说明：本技术 三轴快速刀具伺服机构及其三维力在线检测系统 (Three-axis quick cutter servo mechanism and three-dimensional force online detection system thereof ) 是由 陈远流 李忠伟 陈甫文 居冰峰 于 2020-04-14 设计创作，主要内容包括：本发明提供了一种三轴快速刀具伺服机构及其三维力检测系统,包括：三轴快速刀具伺服机构,其由三个压电陶瓷驱动分别产生三个轴向的位移,通过对称布置的柔性铰链的传动与约束作用,可在末端执行器处实现三个轴向的解耦运动；集成三个电容式位移传感器的位移检测机构,其可检测三轴快速刀具伺服机构三个输入端的位移；集成三个压电陶瓷力传感器的力检测机构,其与三轴快速刀具伺服机构的末端执行器连接,可拆卸,可通过三个力传感器检测值与三个轴向力的线性关系检测出刀尖所受任一空间力在三个轴向的分力。本发明的系统基于压电陶瓷片的正压电效应,将压电陶瓷片作为力传感器,实现了切削过程当中三维力的在线检测。(The invention provides a three-axis quick cutter servo mechanism and a three-dimensional force detection system thereof, comprising: the three-axis quick cutter servo mechanism is driven by three piezoelectric ceramics to generate three axial displacements respectively, and can realize three axial decoupling motions at the end effector through the transmission and constraint action of symmetrically arranged flexible hinges; the displacement detection mechanism integrates three capacitive displacement sensors and can detect the displacement of three input ends of the three-axis quick cutter servo mechanism; the force detection mechanism integrating the three piezoelectric ceramic force sensors is connected with an end effector of the three-axis quick cutter servo mechanism and can be detached, and the component force of any space force applied to the cutter tip in three axial directions can be detected through the linear relation between the detection values of the three force sensors and three axial forces. The system provided by the invention is based on the positive piezoelectric effect of the piezoelectric ceramic piece, and the piezoelectric ceramic piece is used as a force sensor, so that the on-line detection of the three-dimensional force in the cutting process is realized.)

1. The utility model provides a quick cutter servo of triaxial mechanism and three-dimensional power detecting system thereof which characterized in that, quick cutter servo of triaxial mechanism includes:

the base body is provided with a square containing cavity and is provided with a connecting part for fixing the base body on the working platform;

an end effector located within the cavity;

the three piezoelectric ceramics are respectively arranged in the three axial directions of the cavity X, Y, Z, and one end of each piezoelectric ceramics is abutted against the wall of the cavity;

the first guide mechanism is arranged in the containing cavity and comprises four guide pieces which are symmetrically arranged around the end effector from top to bottom and from left to right, each guide piece comprises an X/Y guide part positioned in the middle and connecting parts which are symmetrically arranged and are used for connecting the guide parts and fixing parts at two ends, each connecting part is composed of 2n straight-round flexible hinges which are arranged in parallel, and n is more than or equal to 1; wherein each guide portion located in the direction of the X, Y axis abuts against the other end of the piezoelectric ceramic in that direction;

the first displacement transmission mechanism comprises four groups of X/Y-direction displacement transmission units which are respectively positioned between the four X/Y-direction guide parts and the end effector and are symmetrically arranged around the end effector, and each group of displacement transmission units comprises a pair of displacement transmission pieces formed by connecting two biaxial straight-circular flexible hinges in series;

the second guide mechanism comprises a Z-direction guide part which is abutted against the other end of the piezoelectric ceramic in the Z-axis direction, two end fixing parts which are fixed on the base body, and connecting parts which are symmetrically arranged and are used for connecting the guide part and the two end fixing parts, wherein each connecting part is composed of 2n parallel straight-round flexible hinges, and n is more than or equal to 1;

the second displacement transmission mechanism comprises four displacement transmission pieces which are arranged between the Z-direction guide part and the end effector along the Z-axis direction, and each displacement transmission piece is formed by connecting two double-shaft right-circular flexible hinges in series;

and a displacement detection mechanism integrating three capacitive displacement sensors for detecting displacements of the three guide portions respectively abutting against the piezoelectric ceramics in the three axial directions of X, Y, Z.

2. The three-axis fast tool servo and three-dimensional force sensing system of claim 1 further comprising a force sensing mechanism removably coupled to said end effector, said force sensing mechanism comprising:

a frame having a connection portion detachably connected to the end effector;

the force transmission mechanism comprises a head part, a block-shaped structure, two biaxial right-circular flexible hinges and a tail end fixing part, wherein the head part is integrally arranged and sequentially connected in series and used for mounting a cutter; the two hemispherical surfaces are respectively positioned in the X/Y direction perpendicular to the axis of the force transmission mechanism;

the piezoelectric ceramic force sensor I and the piezoelectric ceramic force sensor II are respectively clamped and fixed on the inner wall of the frame through a fixing block I and a fixing block II and are subjected to certain pretightening force, and the other ends of the fixing block I and the fixing block II are abutted against the two hemispherical surfaces with certain pretightening force;

and the piezoelectric ceramic force sensor III is clamped and fixed on the inner wall of the frame through the tail end fixing part and is subjected to certain pretightening force.

3. The three-axis fast tool servo and the three-dimensional force sensing system thereof of claim 2, further comprising:

the input end of the three-channel charge amplifier module is respectively coupled with the three piezoelectric ceramic force sensors and is used for amplifying polarization charges generated by the piezoelectric ceramic force sensors;

the input end of the AD/DA acquisition card is respectively connected with the output ends of the three capacitive displacement sensors and the output end of the three-channel charge amplifier module and is used for acquiring a voltage signal generated by the capacitive displacement sensors and an amplified polarization charge signal output by the charge amplifier module, and the output end of the AD/DA acquisition card is connected with the input end of a voltage amplifier used for driving piezoelectric ceramics and is used for generating an output voltage signal for controlling the piezoelectric ceramics to generate displacement;

and the upper computer is connected with the control end of the AD/DA acquisition card and is used for receiving the displacement voltage signals acquired by the AD/DA acquisition card and the amplified polarization charge signals, calculating displacement values of the piezoelectric ceramics in three axial directions and the dynamic force applied to the piezoelectric ceramic force sensor based on the signals and controlling the voltage signals to be output, and the voltage signals are transmitted to the piezoelectric ceramics through the AD/DA acquisition card and the precise voltage amplifier so as to precisely control the piezoelectric ceramics to generate displacement.

4. The three-axis fast tool servo mechanism and the three-dimensional force detection system thereof as claimed in claim 3, wherein the magnitude of the three directional forces applied to the force detection mechanism is calculated based on the following linear matrix:

wherein, U₁，U₂，U₃Respectively the outputs corresponding to the stress of the three piezoelectric ceramic force sensors after being amplified by the charge amplifier, F_x，F_y，F_zThe force detection mechanism is subjected to three directional forces.

5. The three-axis fast tool servo mechanism and the three-dimensional force detection system thereof as claimed in claim 4, wherein: the three-channel charge amplifier module is an integrated three-channel charge amplifier, or comprises three single-channel charge amplifiers, or comprises a single-channel charge amplifier and a double-channel charge amplifier.

6. The three-axis fast tool servo mechanism and the three-dimensional force detection system thereof as claimed in claim 5, wherein: the three-channel charge amplifier module is an integrated three-channel charge amplifier which is integrated with three independent amplifying channels, wherein each amplifying channel comprises:

a first amplifier and a second amplifier; the non-inverting terminal of the first amplifier is connected via a resistor R_TCoupled to the non-inverting terminal of the second amplifier Q2, the inverting terminal is connected via a resistor R_GAnd a capacitor C_GThe filter unit formed by parallel connection is grounded, and the output end of the filter unit is coupled with a signal input port of the three-channel charge amplifier; the inverting terminal of the second amplifier is connected via a resistor R_SCoupled to the signal input port of the three-channel charge amplifier, and having its output terminal coupled to the signal output port of the three-channel charge amplifier via a resistor R_FAnd a capacitor C_FThe negative feedback unit formed by parallel connection is coupled with the self inverting terminal.

7. The three-axis fast tool servo mechanism and the three-dimensional force detection system thereof as claimed in claim 6, wherein: the model of the first amplifier is LMP7715, and the model of the second amplifier is LMP 7721.

Technical Field

The invention relates to the technical field of ultra-precision machining, in particular to a novel three-axis quick cutter servo mechanism and a three-dimensional force detection system thereof.

Background

A quick cutter servo system is a mechanical cutting method based on a single-point diamond cutter, and is an effective means for processing a microstructure array which is a main component of an ultra-precise device. With the development of ultra-precision technology, the requirements of special fields on the complexity of optical three-dimensional free surfaces are higher and higher, and the requirements on high-performance manufacturing of microstructures are increasing day by day. Based on the limitation of servo freedom, the traditional single-shaft quick cutter servo system is difficult to meet the manufacturing requirements of complex three-dimensional free surfaces and complex microstructures, so that a two-shaft and three-shaft quick cutter servo mechanism comes up at the right moment. Compared with the cutting process of a single-shaft quick cutter servo mechanism, the cutting process of the three-shaft quick cutter servo mechanism is more complex, and the method is mainly embodied in serious coupling between shafts, unclear cutting states of a cutting edge of a diamond cutter and the surface of a microstructure and the like.

The motion coupling problem of the triaxial quick cutter servo mechanism in X, Y, Z three directions can cause the problems of difficult cutter path planning, influence on the service life of props, influence on the machining precision and the like, so the design key point of the triaxial quick cutter servo mechanism lies in the design of a flexible decoupling mechanism. Three-axis fast tool servo decoupling mechanisms that have been proposed or developed include parallel, tandem, and other forms of decoupling mechanisms. The parallel type three-axis quick cutter servo decoupling mechanism has the structural characteristics that three input ends are independently connected with an output end through flexible guiding and transferring mechanisms in respective directions, namely are connected in parallel and do not influence each other; and each input end corresponds to the output in one direction only. For the series-connection decoupling mechanism, three input ends are connected with an output end through series connection of flexible guiding and transmitting structures in different directions; and each input end corresponds to the output in one direction only. Other forms of decoupling mechanism include: the output in one direction needs more than one input to be generated in a matching way and moves in a matching way; the serial connection and the matching movement are combined; parallel connection and matching movement are combined and the like; these decoupling mechanisms all suffer from one or more of the following problems: the decoupling effect is poor, the rigidity is low, the frequency response is low, the stroke loss is large, the structure is complex, and the processing is difficult.

The cutting force is an important index reflecting the cutting state, and the position of the cutting force is abnormal, so that micro-defects on the surface of the microstructure are often generated. In order to grasp the cutting state of the three-axis fast tool servo mechanism for cutting the complex surface microstructure so as to ensure the integrity of the processed surface microstructure, the cutting forces in three directions generated in the cutting process need to be detected in real time. The existing three-dimensional force detection method comprises a three-dimensional force detection method based on a flexible touch sensor array, a three-dimensional force detection method based on electromagnetic induction, a capacitance type three-dimensional force detection method and the like, and devices related to the methods have the defects of large volume, inflexible structure and the like and are difficult to integrate with a quick cutter servo mechanism for use; meanwhile, the three-dimensional force detection precision of the method is generally low, and the three-axis quick cutter has the characteristic of ultra-low cutting force and also has the irreconcilable contradiction. For the reasons, the traditional dynamic meter and the force sensor are difficult to be integrated into a three-axis quick tool servo mechanism to detect the three-dimensional force on line.

On the other hand, a single-shaft fast tool servo system integrated with a piezoelectric force sensor is available at present and is used for detecting the axial cutting force in the process of servo cutting of the surface microstructure by the single-shaft fast tool. The method uses the piezoelectric ceramic piece as a force sensor, and utilizes the positive piezoelectric effect of the piezoelectric ceramic piece, namely when dynamic force acts on the surface of the piezoelectric ceramic piece, the piezoelectric ceramic piece can generate polarized charges, the positive polarized charges and the negative polarized charges are respectively distributed at two ends of the piezoelectric ceramic piece along the axial direction, and the magnitude of the dynamic force can be reflected by detecting the magnitude of the polarized charges, so that the effect of the force sensor is realized. This quick cutter servo system of unipolar of integrated force transducer has realized the measuring to axial cutting force in the middle of the cutting process to guarantee the on-line monitoring to the surperficial microdefect in the middle of the cutting process. In addition, a force sensor is integrated on a single-shaft quick cutter servo mechanism, a scanning function of using a cutter as a probe is derived through contact force and cutting force closed-loop feedback control, a measuring function is integrated on the basis of a machining function, and a plurality of applications such as cutter cutting edge contour in-situ measurement, relay machining self-positioning and the like are expanded. However, since the single-axis fast tool servo mechanism has only one degree of servo freedom, it is difficult to machine a complicated free optical curved surface and a complicated surface microstructure.

Disclosure of Invention

Based on the background, the invention provides a novel three-axis quick cutter servo mechanism and a three-dimensional force online detection system thereof. Based on a decoupling type three-axis quick cutter servo mechanism, a control system integrating a detection feedback system with displacement detection and feedback and three-dimensional force online detection functions in a cutting process and a precision driving system integrating a precision voltage amplifier is integrated, and the precision decoupling movement of an end effector in three axial directions can be realized.

In order to achieve the purpose, the invention adopts the following technical scheme:

a three-axis quick tool servo mechanism and a three-dimensional force detection system thereof are provided, the three-axis quick tool servo mechanism comprising:

the base body is provided with a square containing cavity and is provided with a connecting part for fixing the base body on the working platform;

an end effector located within the cavity;

the three piezoelectric ceramics are respectively arranged in the three axial directions of the cavity X, Y, Z, and one end of each piezoelectric ceramics is abutted against the wall of the cavity;

the first guide mechanism is arranged in the containing cavity and comprises four guide pieces which are symmetrically arranged around the end effector from top to bottom and from left to right, each guide piece comprises an X/Y guide part positioned in the middle and connecting parts which are symmetrically arranged and are used for connecting the guide parts and fixing parts at two ends, each connecting part is composed of 2n straight-round flexible hinges which are arranged in parallel, and n is more than or equal to 1; wherein each guide portion located in the direction of the X, Y axis abuts against the other end of the piezoelectric ceramic in that direction;

the first displacement transmission mechanism comprises four groups of X/Y-direction displacement transmission units which are respectively positioned between the four X/Y-direction guide parts and the end effector and are symmetrically arranged around the end effector, and each group of displacement transmission units comprises a pair of displacement transmission pieces formed by connecting two biaxial straight-circular flexible hinges in series;

the second guide mechanism comprises a Z-direction guide part which is abutted against the other end of the piezoelectric ceramic in the Z-axis direction, two end fixing parts which are fixed on the base body, and connecting parts which are symmetrically arranged and are used for connecting the guide part and the two end fixing parts, wherein each connecting part is composed of 2n parallel straight-round flexible hinges, and n is more than or equal to 1;

the second displacement transmission mechanism comprises four displacement transmission pieces which are arranged between the Z-direction guide part and the end effector along the Z-axis direction, and each displacement transmission piece is formed by connecting two double-shaft right-circular flexible hinges in series;

and a displacement detection mechanism integrating three capacitive displacement sensors for detecting displacements of the three guide portions respectively abutting against the piezoelectric ceramics in the three axial directions of X, Y, Z.

Further, the system also includes a force detection mechanism removably coupled to the end effector, the force detection mechanism including:

a frame having a connection portion detachably connected to the end effector;

the force transmission mechanism comprises a head part, a block-shaped structure, two biaxial right-circular flexible hinges and a tail end fixing part, wherein the head part is integrally arranged and sequentially connected in series and used for mounting a cutter; the two hemispherical surfaces are respectively positioned in the X/Y direction perpendicular to the axis of the force transmission mechanism;

the piezoelectric ceramic force sensor I and the piezoelectric ceramic force sensor II are respectively clamped and fixed on the inner wall of the frame through a fixing block I and a fixing block II and are subjected to certain pretightening force, and the other ends of the fixing block I and the fixing block II are abutted against the two hemispherical surfaces with certain pretightening force;

and the piezoelectric ceramic force sensor III is clamped and fixed on the inner wall of the frame through the tail end fixing part and is subjected to certain pretightening force.

Further, the system further comprises:

the input end of the three-channel charge amplifier module is respectively coupled with the three piezoelectric ceramic force sensors and is used for amplifying polarization charges generated by the piezoelectric ceramic force sensors;

the input end of the AD/DA acquisition card is respectively connected with the output ends of the three capacitive displacement sensors and the output end of the three-channel charge amplifier module and is used for acquiring a voltage signal generated by the capacitive displacement sensors and an amplified polarization charge signal output by the charge amplifier module, and the output end of the AD/DA acquisition card is connected with the input end of a voltage amplifier used for driving piezoelectric ceramics and is used for generating an output voltage signal for controlling the piezoelectric ceramics to generate displacement;

and the upper computer is connected with the control end of the AD/DA acquisition card and is used for receiving the displacement voltage signals acquired by the AD/DA acquisition card and the amplified polarization charge signals, calculating displacement values of the piezoelectric ceramics in three axial directions and the dynamic force applied to the piezoelectric ceramic force sensor based on the signals and controlling the voltage signals to be output, and the voltage signals are transmitted to the piezoelectric ceramics through the AD/DA acquisition card and the precise voltage amplifier so as to precisely control the piezoelectric ceramics to generate displacement.

Further, the magnitude of the force in three directions borne by the force detection mechanism is calculated based on the following linear matrix:

wherein, U₁，U₂，U₃Respectively the outputs corresponding to the stress of the three piezoelectric ceramic force sensors after being amplified by the charge amplifier, F_x，F_y，F_zThe force detection mechanism is subjected to three directional forces.

Optionally, the three-channel charge amplifier module is an integrated three-channel charge amplifier, or includes three single-channel charge amplifiers, or includes a single-channel and a dual-channel charge amplifier.

Further, the three-channel charge amplifier module is an integrated three-channel charge amplifier, which is integrated with three independent amplification channels, wherein each amplification channel comprises:

a first amplifier and a second amplifier; the non-inverting terminal of the first amplifier is connected via a resistor R_TCoupled to the non-inverting terminal of the second amplifier Q2Resistance R_GAnd a capacitor C_GThe filter unit formed by parallel connection is grounded, and the output end of the filter unit is coupled with a signal input port of the three-channel charge amplifier; the inverting terminal of the second amplifier is connected via a resistor R_SCoupled to the signal input port of the three-channel charge amplifier, and having its output terminal coupled to the signal output port of the three-channel charge amplifier via a resistor R_FAnd a capacitor C_FThe negative feedback unit formed by parallel connection is coupled with the self inverting terminal.

Preferably, the model of the first amplifier is LMP7715, and the model of the second amplifier is LMP 7721.

The invention has the following beneficial effects:

(1) compared with a single-shaft quick cutter servo mechanism integrated with a force sensor, the three-shaft quick cutter servo mechanism integrated with the force sensor in the system has higher degree of freedom, and can realize the processing of a complex surface microstructure.

(2) Compared with the existing three-axis quick cutter servo mechanism, the three-axis quick cutter servo mechanism in the system has high driving displacement resolution, and the minimum driving displacement of three axes can reach within 5 nm.

(3) Compared with the existing decoupling type three-axis quick cutter servo mechanism, the three-axis quick cutter servo mechanism in the system has a good decoupling effect, and the coupling between the three axes is within 3%.

(4) Compared with the existing three-axis quick cutter servo mechanism and three-dimensional force detection means, the system can integrate the force detection system on the three-axis quick cutter servo mechanism, so that the cutting force is detected on line in the cutting process of the three-axis quick cutter servo mechanism; the three-axis quick cutter servo mechanism and the three-dimensional force detection mechanism can be detached, so that the two systems can be used independently.

(5) Compared with the existing triaxial force detection means, the system has high sensitivity, and the cutting force can be recognized within 10mN at the minimum in each axial direction.

Drawings

FIG. 1 is a schematic diagram of a three-axis fast tool servo structure according to the present invention.

FIG. 2 is a schematic view of a Z-direction driving structure of a three-axis fast tool servo structure according to the present invention.

FIG. 3 is a schematic view of the installation of a displacement sensor of a three-axis fast tool servo structure according to the present invention.

FIG. 4 is a diagram showing the results of the resolution test of the three-axis driving displacement according to the present invention.

Fig. 5 is a schematic diagram of the force detection structure of the present invention.

FIG. 6 is a schematic diagram of a three-axis fast tool servo mechanism integrated with a force detection mechanism according to the present invention.

Fig. 7 is a schematic diagram of three-dimensional force sensing measurement according to an embodiment of the present invention.

FIG. 8 is a diagram illustrating calibration results of a three-axis force sensor according to an embodiment of the present invention, wherein (a) is a dynamic force variation curve of output voltage variation of three charge amplifiers along with different X-axis directions; (b) the change of the output voltage of the three charge amplifiers is along with the change curve of the dynamic force acting in different X-axis directions; (c) the change of the output voltage of the three charge amplifiers is along with the change curve of the dynamic force acting in different X-axis directions.

Detailed Description

For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.