Direct attitude feedback control method and direct attitude feedback control machine

Abstract

The present invention provides a direct attitude feedback control method and a direct attitude feedback control machine, which directly measures the actual attitude of a tool relative to a workpiece, performs attitude error compensation, and eliminates geometric errors and thermal errors in the machine structure and driving mechanism. The attitude feedback control machine is provided with a double ball bar attitude measurement mechanism at the tool end and the base end, which measures the actual attitude of the tool during movement or positioning, obtains a tracking attitude error between the encoder defined attitude and the set attitude, and obtains a connection attitude error between the actual attitude and the encoder defined attitude. The controller performs position feedback control on the tracking attitude error and performs attitude compensation control on the connection attitude error, so that the geometric error and thermal error of the direct attitude feedback control machine are eliminated.

Description

Technical Field

[0001] The present invention relates to a feedback control method and a feedback control machine, and in particular to a direct attitude feedback control method and a direct attitude feedback control machine. Background Art

[0002] When the linear axis or rotating axis in the driving mechanism of a CNC machine tool or an industrial joint machine performs positioning motion, there will be positioning errors, which are generally expressed by six error terms. Taking the X-axis or worktable of a CNC machine tool performing linear positioning motion as an example, the positioning error includes the linear errors of the worktable in the X, Y, and Z directions, and the roll, pitch, and yaw rotation errors of the X, Y, and Z axis rotations. There are also verticality or parallelism errors between the axes in the driving mechanism. The mechanism parameters between the various rotating axes in the arm of an ideal industrial joint machine can be described by, for example, DH mechanism parameters, but due to manufacturing and assembly factors, each mechanism parameter also has geometric errors. Therefore, how to effectively reduce the positioning error of the machine has always been the goal of the industry.

[0003] In addition to geometric errors in the drive mechanism, the machine will also experience thermal deformation during operation due to internal heat sources and external environmental temperature changes or heat sources. Internal heat sources include friction between moving components, such as spindle bearings, ball screw nuts, guide rails, etc., and heat generated during servo motor energy conversion. External heat sources include ambient temperature, operator body temperature or sunlight. To improve the accuracy of the machine, the thermal error of the machine must be eliminated or reduced, such as using a temperature sensor to measure the actual temperature of the machine structure and components or assemblies, and using the thermal error model to calculate the thermal error of the machine and compensate for it.

[0004] The geometric errors and thermal errors in the machine structure and drive mechanism ultimately cause posture errors when the tool moves or positions relative to the workpiece, including position errors and pointing errors. Advanced controllers can establish a geometric error model for the machine. For example, a laser interferometer can be used to measure the 21 geometric errors of a three-linear-axis machine and perform geometric error compensation for the machine. However, these 21 geometric errors will change due to the temperature state of the machine, affecting the compensation effect.

[0005] In US Patents US5681981A, US6226884B1 and US6662461B2, there are measuring devices and methods with Stewart Platform Mechanism, in which the first platform and the second platform are connected by six retractable measuring rods to form a parallel mechanism. By measuring the length of each measuring rod, the coordinate relationship between the first platform and the second platform is calculated in the measuring computer. In US Patent US7810248B2, there is a coordinate measuring machine, in which the telescopic rod connecting the two platforms is specially arranged to form a working space that is conducive to the entry and exit of the workpiece. In US Patent US2019 / 0072373A1, there is a six-link coordinate measuring machine, in which the telescopic rod connecting the two platforms has a pneumatic bearing design.

[0006] These measuring devices or machines with Stewart platform mechanisms have many disadvantages. Due to the geometric errors and thermal errors in the mechanism parameters, the measurement accuracy of these measuring devices is not high and their applications are limited. In Taiwan Patent TWI585363B "Double ball bar system for measurement and error compensation method thereof" of the same applicant, a geometric error and thermal error compensation method for double ball bars is proposed, but there are still some shortcomings.

[0007] The technical problem to be solved by the present invention is the geometric errors and thermal errors in the machine structure and drive mechanism. These geometric errors and thermal errors cause the actual posture of the machine tool relative to the workpiece to deviate from the set posture, affecting the positioning accuracy and processing accuracy of the machine. Summary of the invention

[0008] In order to provide a more accurate machine, the present invention provides a direct attitude feedback control method and a direct attitude feedback control machine.

[0009] According to an embodiment of an aspect of the present invention, a direct attitude feedback control method is provided, which is applied to a direct attitude feedback control machine, the direct attitude feedback control machine comprises a controller, a double ball bar attitude measurement mechanism, a plurality of motors and a tool, the double ball bar attitude measurement mechanism is arranged between a base end and a tool end of the direct attitude feedback control machine and comprises a tool end platform arranged at the tool end, a base end platform arranged at the base end, at least six working double ball bars connected to the tool end platform and the base end platform, and at least one reference double ball bar arranged at a reference plate, the tool end platform comprises at least three ball sockets, the base end platform comprises at least three ball sockets, the direct attitude feedback control method combines an attitude compensation control with a position feedback control, the attitude compensation control comprises an initialization step, a coordinate conversion relationship establishment step, an actual attitude calculation step and a position compensation value calculation step. In the initialization step, the controller is made to establish a center distance function of the aforementioned at least one reference double ball bar and each working double ball bar, and establish a coordinate conversion relationship between a tool platform coordinate system and a base platform coordinate system of the double ball bar attitude measurement mechanism. In the coordinate transformation relationship establishment step, the controller establishes a coordinate transformation relationship between the basic platform coordinate system and a reference coordinate system according to a built-in or loaded setting value or an on-machine measurement. In the actual posture calculation step, the controller reads a working displacement measurement value of each working double ball rod to calculate an actual posture of the tool. In the position compensation value calculation step, the controller obtains an incremental position compensation value and a position compensation value of each motor according to a compensation target posture and an actual posture, wherein the posture compensation control performs a mechanism positive conversion calculation by subtracting the position compensation value from an actual position value of each motor to obtain an encoder-defined posture, and obtains a connection posture error from the difference between the encoder-defined posture and the actual posture, obtains a tracking posture error from the difference between a set posture and the encoder-defined posture, obtains an actual posture error from the set posture and the actual posture obtained by measurement, and obtains the position compensation value of each motor from the connection posture error or the actual posture error. The posture compensation control uses a compensation controller of each motor, and the compensation controller generates a compensated driving value of each motor based on the position compensation value of each motor. The position feedback control uses the position controller of each motor, and obtains the driving value based on the difference between the position setting value and the actual position value. The driving value is added to the compensated driving value and output to the driver of each motor. The position compensation value of each motor remains valid until the posture compensation control is updated.

[0010] According to the aforementioned multiple embodiments of the direct attitude feedback control method, the sampling time of the attitude compensation control is greater than or equal to the sampling time of the position feedback control.

[0011] According to the aforementioned multiple embodiments of the direct attitude feedback control method, the compensation target attitude is an encoder defined attitude or a set attitude.

[0012] According to the aforementioned multiple embodiments of the direct attitude feedback control method, the incremental position compensation value of each motor is obtained by using the Jacobian inverse matrix.

[0013] According to the above-mentioned multiple embodiments of the direct attitude feedback control method, the incremental position compensation value of each motor is obtained by subtracting the equivalent position actual value of each motor from the attitude position value defined by the encoder of each motor.

[0014] According to multiple embodiments of the direct attitude feedback control method described above, the compensation controller is a proportional controller.

[0015] According to the multiple embodiments of the direct attitude feedback control method described above, the compensation controller of each motor is the same as the position controller. At this time, the position compensation value of each motor is added to the position setting value of each motor and then input into the position controller to obtain the compensated drive value.

[0016] According to the above-mentioned multiple embodiments of the direct attitude feedback control method, a position compensation value of each motor is subjected to low-pass filtering to obtain a position compensation value without vibration factors.

[0017] According to the above-mentioned multiple embodiments of the direct attitude feedback control method, in the initialization step, at least one motor is driven to make each working double ball bar pass through the origin to initialize the center distance function of each working double ball bar built in or loaded into the controller.

[0018] According to the multiple embodiments of the direct attitude feedback control method described above, the on-board measurement includes driving at least two motors to position respectively, obtaining a reference coordinate system from the measurement results of the double-ball-bar attitude measurement mechanism, and obtaining a coordinate conversion relationship between the basic platform coordinate system and the reference coordinate system.

[0019] According to the above-mentioned multiple embodiments of the direct attitude feedback control method, in the position compensation value calculation step, a single approximation method or an iterative multiple approximation method is used to calculate the incremental position compensation value of each motor.

[0020] According to multiple embodiments of the direct attitude feedback control method described above, a controller reads in the thermal error measurement value of a reference double ball bar, calculates and compensates for the thermal errors of various mechanism parameters of the double ball bar attitude measurement mechanism based on the thermal error measurement value, including the thermal errors of the ball socket positions on the tool end platform and the base end platform and the thermal errors of the center distances of the working double ball bars.

[0021] According to the aforementioned multiple embodiments of the direct attitude feedback control method, in the actual attitude calculation step, the controller reads out each working displacement measurement value synchronously latched by a trigger signal, and calculates the coordinate position of the center of the measuring ball at the end of the tool.

[0022] According to the above-mentioned multiple embodiments of the direct attitude feedback control method, the direct attitude feedback control machine further includes a bracket for mounting the basic end platform, and in the actual attitude calculation step, the thermal error of the bracket height is calculated and compensated according to the thermal error measurement value of the reference double ball bar.

[0023] According to the above-mentioned multiple embodiments of the direct attitude feedback control method, in the actual attitude calculation step, the thermal error of the tool length is calculated and compensated according to the thermal error measurement value of the reference double ball bar.

[0024] According to the aforementioned multiple embodiments of the direct attitude feedback control method, the controller performs spectrum analysis on the actual attitude to obtain vibration information of the direct attitude feedback control machine.

[0025] According to an embodiment of another aspect of the present invention, a direct posture feedback control machine is provided, which includes a machine body, multiple motors, a controller and a double-ball-bar posture measurement mechanism, the machine body includes a tool end and a base end, and the tool end is provided with a tool, the motor is provided on the machine body, the controller drives the motor to move the tool relative to a workpiece at the base end, the double-ball-bar posture measurement mechanism is provided between the base end and the tool end and includes a tool end platform, a base end platform, at least six working double-ball bars, a reference plate and at least one reference double-ball bar, the tool end platform is located at the tool end and includes at least three ball sockets; the base end platform is located at the base end and includes at least three ball sockets, at least six working double-ball bars, connected between the ball sockets of the tool end platform and the ball sockets of the base end platform, each working double-ball bar includes two measuring balls, and the position of each working double-ball bar is measured. A displacement sensor measures the distance between the centers of two measuring balls, a reference plate includes at least two reference ball sockets, a reference double ball rod includes two reference measuring balls, which are arranged between at least two reference ball sockets on the reference plate, and a displacement sensor is used to measure the distance between the centers of the two reference measuring balls, wherein a controller uses the reference double ball rod as a device for measuring the thermal error of the mechanism parameters of the double ball rod posture measurement mechanism, and uses the double ball rod posture measurement mechanism as a device for measuring the actual posture of the tool, and the controller has a posture compensation control, a connection posture error is obtained by the difference between an encoder-defined posture and the actual posture, a tracking posture error is obtained by the difference between a set posture and the encoder-defined posture, and a position compensation value and a compensation drive value of each motor are obtained from the connection posture error, and the compensation drive value is added to a drive value obtained by a position controller of each motor and output to a driver of each motor.

[0026] According to the multiple embodiments of the direct attitude feedback control machine described above, it may further include a spindle seat and a spindle, wherein the spindle seat is disposed on the machine body, the spindle is connected to the spindle seat and includes a spindle housing, wherein the tool end platform is fixed on the spindle seat or the spindle housing.

[0027] According to the aforementioned multiple embodiments of the direct attitude feedback control machine, the direct attitude feedback control machine may be a multi-axis machine tool, a multi-axis joint machine or a parallel linkage drive machine.

[0028] According to the aforementioned multiple embodiments of the direct attitude feedback control machine, the tool may be a tool, a measuring probe, a trigger probe, a conjugate focus sensor, a displacement measuring laser, or an optical measuring lens.

[0029] According to the aforementioned multiple embodiments of the direct posture feedback control machine, the tool can generate a trigger signal to synchronously latch the working displacement measurement values ​​of each working double ball rod with the trigger signal.

[0030] According to the aforementioned multiple embodiments of the direct attitude feedback control machine, a reference ball may be further included, which is disposed on the base end platform or the workbench.

[0031] According to the aforementioned multiple embodiments of the direct posture feedback control machine, a tool length measuring mechanism may be further included, which is disposed on the base end platform or the workbench.

[0032] According to the aforementioned multiple embodiments of the direct posture feedback control machine, the multiple ball sockets on the tool end platform and the base end platform may have an asymmetrical distribution.

[0033] According to the aforementioned multiple embodiments of the direct attitude feedback control machine, the ball sockets on the base end platform and the tool end platform can be fixed on a material with a thermal expansion coefficient between 0 ppm / °C (μm / m / °C) and 2 ppm / °C.

[0034] According to the aforementioned multiple embodiments of the direct attitude feedback control machine, it may further include a bracket, and the base end platform is installed on the bracket.

[0035] According to the aforementioned multiple embodiments of the direct attitude feedback control machine, the controller may include a real-time communication network, and each working dual ball bar and the reference dual ball bar transmit back each working displacement measurement value and thermal error measurement value through the real-time communication network.

[0036] According to the aforementioned multiple embodiments of the direct attitude feedback control machine, wherein the real-time communication network is a real-time Ethernet communication network (EtherCAT).

[0037] According to the aforementioned multiple embodiments of the direct attitude feedback control machine, the displacement sensor of each working double ball bar and the reference double ball bar can be a laser interferometer, an optical ruler or a magnetic ruler. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic diagram showing a direct attitude feedback control machine according to an embodiment of the present invention;

[0039] Figure 2 A schematic diagram showing a direct attitude feedback control machine according to another embodiment of the present invention;

[0040] Figure 3 A schematic diagram showing a direct attitude feedback control machine according to another embodiment of the present invention;

[0041] Figure 4 Show Figure 3 A block diagram of a control architecture of a direct attitude feedback control machine of an embodiment;

[0042] Figure 5 A block flow chart showing a direct attitude feedback control method according to the present invention;

[0043] Figure 6 Show Figure 5 A schematic diagram of the posture of a tool of the direct posture feedback control method of an embodiment;

[0044] Figure 7 Show Figure 5 A control flow chart of the direct attitude feedback control method of the embodiment;

[0045] Figure 8 Show Figure 5 Another control flow chart of the direct attitude feedback control method of the embodiment;

[0046] Fig. 9 Show Figure 5 Another control flow chart of the direct attitude feedback control method of the embodiment;

[0047] Fig.10 Show Figure 5 Yet another control flow chart of the direct attitude feedback control method of the embodiment; and

[0048] Fig.11 A schematic diagram of a double-ballbar attitude measurement mechanism of a direct attitude feedback control machine according to another embodiment of the present invention is shown.

[0049] The reference numerals are described as follows:

[0050] 10, 10a, 10b: Direct attitude feedback control machine

[0051] 11: Base

[0052] 11a, 11b, 11d: Six-axis robotic arm

[0053] 12, 12a, 12b: Workbench

[0054] 13b: Bracket

[0055] 110, 110a, 110b: Workpiece

[0056] 120: Heightening block

[0057] 120a: Workpiece mounting seat

[0058] 130: Knife length measuring device

[0059] 131a, 131b: Reference sphere

[0060] 200b: Controller

[0061] 210b: Window operation module

[0062] 211b: Human-machine interface

[0063] 220b: Motion control core module

[0064] 221b: Interpreter

[0065] 222b, 222d: Interpolator

[0066] 2221d: Path Interpolator

[0067] 2222d: Pointing to interpolator

[0068] 223b, 223d: Acceleration and deceleration planner

[0069] 224d: Inverse converter

[0070] 225d: Positive converter

[0071] 226d: Time delay element

[0072] 227d: Drive system

[0073] 228d: Integrator

[0074] 230b: Real-time communication network

[0075] 240b: Drive

[0076] 250b: Digital counter

[0077] 3: Z motion platform

[0078] 300, 300a, 300b, 300c, 300d: Double ball bar attitude measurement mechanism

[0079] 310, 310a, 310b, 310c: Basic terminal platform

[0080] 311, 311a, 311b: Positioning layer

[0081] 312, 312a, 312b: Support layer

[0082] 320, 320a, 320b, 320c: Tool-side platform

[0083] 321, 321a, 321b: Positioning layer

[0084] 322, 322a, 322b: Support layer

[0085] 330, 330a, 330b, 330c: Working double ball bar

[0086] 4: Spindle seat

[0087] 400, 400a, 400b: Reference double club

[0088] 5: Spindle

[0089] 500, 500a, 500b: Reference board

[0090] 510, 520: Magnetic ball socket

[0091] 6, 6a, 6b: Tools

[0092] 800b: Motor

[0093] B1~B6: Ball socket

[0094] P1~P6: Ball socket

[0095] Y: Axis

[0096] {B}: Basic platform coordinate system {P0}: Starting tool platform coordinate system {P n}: Actual tool platform coordinate system {R}: Reference coordinate system

[0097] 91: Position feedback control

[0098] 911: Position Controller

[0099] 92: Attitude compensation control

[0100] 921: Compensation Controller

[0101] S01: Initialization step

[0102] S02: Coordinate transformation relationship establishment step S03: Actual posture calculation step

[0103] S04: Position compensation value calculation step FF: Feedforward control

[0104] J -1 : Inverse Jacobian matrix

[0105] P A: Actual posture

[0106] P E : Encoder defines the pose

[0107] P r : Reference posture

[0108] P S : Set posture

[0109] E a : Actual attitude error

[0110] E l : Connection attitude error

[0111] E f : Tracking attitude error

[0112] V cmd，i : Motor drive value

[0113] θ i，a ,θ 1，a ,θ 6，a : Equivalent position actual value

[0114] θ i，E ,θ 1，E ,θ 6，E : Encoder defines the attitude position value

[0115] θ i，s ,θ1 ，s ~θ 6，s : Position setting value

[0116] θ i，enc ,θ 1，enc ,θ 6，enc : Actual position value

[0117] Δθ i，comp , Δθ 1，comp , Δθ 6，comp : Incremental position compensation value

[0118] θ i，comp ,θ 1，comp ,θ 6，comp : Position compensation value

[0119] Coordinate transformation relationship between tool platform coordinate system and basic platform coordinate system

[0120] Coordinate transformation relationship between the actual tool platform coordinate system and the basic platform coordinate system

[0121] Coordinate transformation relationship between the actual tool endpoint coordinate system and the basic platform coordinate system

[0122] Coordinate transformation relationship between tool end coordinate system and basic platform coordinate system

[0123] R T B : Coordinate transformation relationship between the basic platform coordinate system and the reference coordinate system

[0124] Coordinate transformation relationship between tool end coordinate system and reference coordinate system

[0125] Coordinate transformation relationship between tool endpoint coordinate system and tool platform coordinate system

[0126] Coordinate transformation relationship between the actual tool end coordinate system and the reference coordinate system under the encoder defined posture

[0127] Coordinate transformation relationship between the actual tool endpoint coordinate system and the actual tool platform coordinate system Coordinate transformation relationship between actual tool end coordinate system and reference coordinate system DETAILED DESCRIPTION

[0128] The embodiments of the present invention will be described below with reference to the accompanying drawings. For the purpose of clarity, many practical details will be described together in the following description. However, the reader should understand that these practical details should not be used to limit the present invention, that is, in some embodiments of the present invention, these practical details are not necessary. In addition, in order to simplify the drawings, some conventional structures and elements will be shown in a simple schematic manner in the drawings; and repeated elements may be represented by the same number or similar number.

[0129] In addition, in this article, when a certain element (or mechanism or module, etc.) is "connected", "set" or "coupled" to another element, it may refer to that the element is directly connected, directly set or directly coupled to another element, and it may also refer to that a certain element is indirectly connected, indirectly set or indirectly coupled to another element, that is, there are other elements between the element and the other element. When it is clearly stated that a certain element is "directly connected", "directly set" or "directly coupled" to another element, it means that there are no other elements between the element and the other element. The terms first, second, third, etc. are only used to describe different elements or components, and there is no restriction on the elements / components themselves. Therefore, the first element / component can also be renamed as the second element / component. And the combination of elements / components / mechanisms / modules in this article is not a generally known, conventional or existing combination in this field, and it cannot be determined whether the combination relationship is easy to be easily completed by the general knowledge in the technical field based on whether the elements / components / mechanisms / modules themselves are existing.

[0130] The main technical feature used in the present invention is that a double-ball-bar attitude measurement mechanism with thermal error compensation is installed on the machine to directly measure the actual attitude of the tool relative to the workpiece and obtain the actual attitude error. After processing, position compensation values ​​and compensation drive values ​​are obtained for each motor to perform attitude error compensation control. In this way, the attitude error of the tool relative to the workpiece caused by geometric errors and thermal errors in the machine structure and drive mechanism can be eliminated, thereby improving the accuracy of the machine.

[0131] One object of the present invention is to provide a direct attitude feedback control method, which obtains the attitude error by directly measuring the actual attitude of the tool relative to the workpiece, that is, the actual position of the tool end point and the actual direction of the tool, and drives the motor to perform attitude compensation control to eliminate geometric errors and thermal errors in the machine structure and drive mechanism.

[0132] The machine to which the direct attitude feedback control method of the present invention is applied can be called a direct attitude feedback control machine. The driving mechanism of the direct attitude feedback control machine can be a series type or a parallel type, with multiple motors driving the tool to move relative to the workpiece. The direct attitude feedback control machine can be a multi-axis machine tool or a multi-axis joint robot arm, or a parallel connecting rod driving machine (or parallel mechanism machine). A double ball bar attitude measurement mechanism is arranged between the tool end and the base end of the direct attitude feedback control machine. The double ball bar attitude measurement mechanism includes a tool end platform installed on the tool end, a base end platform installed on the base end, and at least six working double ball bars. The tool end platform and the base end platform each include at least three ball sockets; the six working double ball bars connect the ball sockets on the tool end platform and the ball sockets on the base end platform. The double-ball-bar attitude measurement mechanism may further include a reference plate and at least one reference double-ball-bar, wherein the reference plate includes a plurality of reference ball sockets, and at least one reference double-ball-bar is placed on two reference ball sockets of the reference plate. The reference double-ball-bar is used for thermal error compensation of the mechanism parameters of the double-ball-bar attitude measurement mechanism. The controller of the direct attitude feedback control machine uses the double-ball-bar attitude measurement mechanism to measure the actual attitude of the tool during movement or positioning, and performs direct attitude feedback control.

[0133] In the direct attitude feedback control machine of the present invention, individual sensors are not configured for the geometric errors and thermal errors in the machine structure and the driving mechanism. Instead, double-ball-bar attitude measurement mechanisms are set at the tool end and the base end. The six-dimensional attitude error of the tool relative to the workpiece caused by the geometric errors and thermal errors of each component in the machine structure and the driving mechanism is measured by the double-ball-bar attitude measurement mechanism, and then the position compensation value of each motor is obtained. The compensation controller inputs the position compensation value to generate the compensation driving value of the motor, which is added to the driving value of the motor generated by the position controller and output to the driver to drive the motor, making the direct attitude feedback control machine of the present invention an ideal machine without mechanism parameter error, geometric error and thermal error.

[0134] As a measurement device for direct attitude feedback control, the measurement accuracy of the double ball bar attitude measurement mechanism must be very high, and the measurement accuracy of displacement and rotation angle should preferably be micrometer and arc second level or better. The double ball bar attitude measurement mechanism itself also has geometric errors and thermal errors, including the geometric errors and thermal errors of the working double ball bars, and the position errors and thermal errors of the ball socket centers on the tool end platform and the basic end platform. The existing parallel measurement mechanism cannot accurately eliminate these errors and has limited accuracy.

[0135] The working double ball bar needs to use its displacement measurement value to derive the absolute distance between the centers of its two end measuring balls, referred to as the center distance. In order to improve the accuracy of the double ball bar posture measurement mechanism, in the direct posture feedback control machine of the present invention, the controller can be built-in or loaded with the center distance function of each working double ball bar. This center distance function takes the displacement measurement value of the working double ball bar as input and its accurate center distance as output. The center distance function of each working double ball bar is started in the initialization step. This center distance function can be established with the help of a calibration plate. A plurality of magnetic seats are arranged on this calibration plate. The center distance between two specific magnetic seats is known. The calibration plate provides at least two known center distances. When calibrating, the working double ball bar is placed on two magnetic seats with known center distances. At this time, the displacement measurement value of the working double ball bar and the known center distance constitute a calibration point. The center distance function of the working double ball bar can be established with at least two calibration points. The more calibration points there are, the better the accuracy.

[0136] The present invention can further provide at least one reference double ball bar disposed on the reference plate, and the thermal error of the working double ball bar caused by the change of the ambient temperature is obtained based on the thermal error measurement value of the reference double ball bar, and compensated by the controller. On the other hand, the thermal error of the center position of each ball socket on the tool end platform and the basic end platform is obtained based on the thermal error measurement value of the reference double ball bar, and compensated. In this way, in the direct attitude feedback control machine of the present invention, the geometric errors and thermal errors of all mechanism parameters in the double ball bar attitude measurement mechanism are compensated, so that when the ambient temperature changes within 5°C, the measurement accuracy of the double ball bar attitude measurement mechanism can still reach the micron and arc second level. In the direct attitude feedback control machine of the present invention, the thermal error of the tool, such as the thermal error of the tool or the measuring probe length, is also compensated based on the thermal error measurement value of the reference double ball bar. Through the design and method of the present invention, the direct attitude feedback control machine of the present invention has a positioning accuracy of micron and arc second level.

[0137] The center distance function of the reference double ball bar can be built-in in the controller or loaded during initialization. When the working double ball bar or the reference double ball bar uses an absolute displacement sensor, the controller can directly start its center distance function after the machine is turned on; when the working double ball bar uses an incremental displacement sensor, the controller can start its center distance function by driving the machine, such as moving the Z axis, to make each working double ball bar pass the origin. When the reference double ball bar uses an incremental displacement sensor, since it does not have a driving mechanism, additional means are required, such as manually or using an auxiliary device to make it pass the origin to start its center distance function.

[0138] The direct attitude feedback control machine can be a multi-axis machine tool or a multi-axis joint machine. The tool installed and used on the machine can be a tool driven by the spindle, such as a milling cutter, or a fixed measuring tool, including a measuring probe, a conjugate focusing sensor, a laser displacement measuring device, an optical measuring lens, etc. In order to accurately calculate the position of the tool end point and the tool orientation, the controller must synchronously read out the working displacement measurement values ​​of all working double ball rods, which can be performed through the timer interrupt of the real-time timer. When the tool is a measuring probe, the working displacement measurement values ​​of all working double ball rods can be synchronously latched through a trigger signal and then read out by the controller. When the tool is a measuring probe, a reference ball can be set on the basic end platform or the workbench where the workpiece is placed to calibrate the center coordinate position of the measuring ball at the end of the probe; and if the tool is a cutting tool, a tool length measuring device can be set on the basic end platform or the workbench where the workpiece is placed to calibrate the tool length.

[0139] In the direct attitude feedback control machine of the present invention, the tool end platform and the base end platform can be designed independently and installed on the tool end and the base end of the direct attitude feedback control machine respectively through appropriate adapters. In addition, they can also be designed as an integral part with the direct attitude feedback control machine. The key point is that the tool end platform must be able to sensitively respond to the tool end displacement and tool pointing changes caused by the geometric error and thermal error of the machine, and the base end platform must consider the entry and exit and fixing method of the workpiece. In one embodiment, the direct attitude feedback control machine is a multi-axis machine tool with a spindle, and the tool end platform is fixed to the end face of the spindle seat or the spindle housing through an adapter, and can produce displacement and deflection along with the thermal deformation of the spindle. In another embodiment, the direct attitude feedback control machine is a multi-axis joint robot arm, the tool end platform is fixed on the tool mounting seat, and the tool is fixed on the tool end platform.

[0140] The tool end platform and the basic end platform each include three or six ball sockets. When the tool end platform and the basic end platform each include three ball sockets, two working double ball rods can be connected to one ball socket; when the tool end platform and the basic end platform each include six ball sockets, one working double ball rod can be connected to one ball socket, and the tool end platform and the basic end platform are provided with at least six working double ball rods in total, thereby forming a Stewart platform mechanism. For a standard Stewart platform mechanism, the positions of the six ball sockets on the tool end platform and the basic end platform are symmetrically periodically distributed, for example, periodically distributed on a circle at angular intervals of 20 degrees and 100 degrees. In order to avoid interference between the working double ball rods or with machine components, or to increase the working stroke in a specific direction, the positions of some ball sockets can also be deliberately offset, and the maximum center distance and the minimum center distance of each working double ball rod are coordinated with the distribution of the ball sockets and can be different from each other. In one embodiment, the six ball sockets on the basic end platform are asymmetrically distributed in a semicircular range to avoid the Z motion platform and the spindle seat, and the six ball sockets on the tool end platform also have corresponding position offsets.

[0141] The ball sockets on the tool end platform and the basic end platform may be provided with magnets, allowing the ball at the end of the working double ball rod to be adsorbed on the ball sockets to form a ball bearing structure. The ball sockets may be, for example, three-point or arc-supported adsorption ball sockets, in which case there is sliding contact between the ball sockets and the balls, or a ball may be provided between the balls and the ball sockets to form rolling contact, which has better wear resistance. In another embodiment, the ball sockets on the tool end platform or the basic end platform may be replaced with balls, in which case the end of the working double ball rod is the matching ball socket.

[0142] In the direct attitude feedback control machine of the present invention, the ball sockets on the tool end platform and the basic end platform and the ball at the end of the working double ball rod constitute a ball bearing structure (referred to as ball bearing), and the center position of this ball bearing must not be affected by external forces and heat. In order to reduce or eliminate the thermal error caused by the change of ambient temperature in the center position of each ball bearing on the tool end platform and the basic end platform, the ball socket is preferably fixed on a material with a thermal expansion coefficient of less than 2ppm / ℃, or even a material with a thermal expansion coefficient close to zero (less than 0.1ppm / ℃), such as INVAR Invar alloy, SUPER INVAR super Invar alloy, carbon fiber composite material, alloys or quartz, etc., or glass-ceramics, e.g. Glass-ceramic or Glass-ceramic.

[0143] In a direct attitude feedback control machine, the tool and the workpiece can be inside or outside the space covered by the tool end platform, the base end platform and the six working double ball bars. In one embodiment, the direct attitude feedback control machine is a three-linear axis machine tool, and the spindle (high-speed spindle) is driven by the X-axis and the Z-axis, the workpiece is fixed on the Y-axis worktable, the tool end platform is fixed on the spindle housing through an adapter, the base end platform is a hollow ring and is fixed on the Y-axis worktable, the workpiece is fixed in the hollow part of the base end platform, and the six working double ball bars are connected between the tool end platform and the base end platform, and the tool and the workpiece are covered inside. In addition, a tool length measuring device can be installed on the base end platform to calibrate the tool length.

[0144] In another embodiment, the direct attitude feedback control machine includes a six-axis robot arm and a workbench, the workbench can be made of granite, the six-axis robot arm is fixed on the workbench, the tool end is a tool mounting seat at the end of the six-axis robot arm, the base end is a workpiece mounting surface on the workbench, the tool can be a measuring probe, the tool end platform can be fixed on the tool mounting seat, the measuring probe can be fixed on the tool end platform, the base end platform can be fixed on the workbench and has a hollow part, the workpiece is placed in the hollow part, six working double ball rods connect the tool end platform and the base end platform, the measuring probe and the workpiece are located in the space covered by the tool end platform, the base end platform and the six working double ball rods, the measuring probe has a trigger signal, and the controller can synchronously read the displacement measurement values ​​of the six working double ball rods to calculate the center coordinate position of the measuring ball at the end of the measuring probe, and a reference ball can be fixed on the base end platform or on the workbench for coordinate correction. This direct attitude feedback control machine can be used for coordinate measurement of small workpieces.

[0145] In another embodiment, the direct attitude feedback control machine includes a six-axis robot arm, a workbench and a bracket, the tool is a measuring probe, the workpiece is fixed on the workbench, the bracket is also fixed on the workbench, the basic end platform is fixed on the bracket, the tool end platform is fixed on the tool mounting surface of the six-axis robot arm, and six working double ball bars connect the tool end platform and the basic end platform to form an inverted double ball bar attitude measurement mechanism, so that the measuring probe and the workpiece are outside the space covered by the tool end platform, the basic end platform and the six working double ball bars. A reference ball can be fixed on the workbench for coordinate correction. The advantage of the direct attitude feedback control robot arm of this embodiment is that it can be used for coordinate measurement of small and medium-sized workpieces, and the operation and entry and exit of the workpiece are more convenient. Since the basic end platform is fixed on the bracket, the bracket is preferably made of a material with a low thermal expansion coefficient and high strength, such as INVAR alloy or Alloy to avoid the thermal error of the bracket affecting the measurement results. In addition, the thermal error of the bracket height can also be compensated to ensure the accuracy of the direct attitude feedback control machine.

[0146] In one embodiment, the controller can read back the working displacement measurement value of each working double ball bar, the thermal error measurement value of the reference double ball bar and the actual position value of the motor through a real-time communication network, such as an Ethernet real-time communication network (EtherCAT), and also send out the motor drive value, which can greatly reduce the number of wiring. In the double ball bar posture measurement mechanism, the displacement sensor of the working double ball bar can be an absolute or incremental laser interferometer, an optical ruler or a magnetic ruler. After initialization, the working double ball bar has an absolute center distance.

[0147] The present invention provides a direct attitude feedback control method, wherein a tool platform coordinate system is defined on a tool end platform, a basic platform coordinate system is defined on a basic end platform, and a reference coordinate system is defined on a machine. The coordinate position of the ball bearing center in the tool platform coordinate system, the coordinate position of the ball bearing center in the basic platform coordinate system, and the center distance of six working double ball bars constitute the mechanism parameters of a double ball bar attitude measurement mechanism. When performing direct attitude feedback control, the mechanism parameters are used to perform mechanism forward and inverse conversion calculations, and the six-dimensional coordinate conversion relationship between the tool platform coordinate system and the basic platform coordinate system is calculated, and then the actual posture of the tool in the reference coordinate system is calculated, including three positions and three rotation angles.

[0148] The direct attitude feedback control method of the present invention can obtain the thermal error of the mechanism parameters of the double-ball bar attitude measurement mechanism by referring to the thermal error measurement value of the double-ball bar, including the thermal error of the center distance of the working double-ball bars and the thermal error of the center position of each ball bearing on the tool end platform and the basic end platform, and compensate them, and use the compensated mechanism parameters to perform mechanism conversion calculations.

[0149] The direct attitude feedback control machine has static mechanism parameter errors and geometric errors in the machine structure and drive mechanism, as well as quasi-static thermal errors. When the controller drives the tool to move relative to the workpiece, there is a dynamic state error, which ultimately causes the position error of the tool end point and the tool pointing error, that is, the tool attitude error. The mechanism parameters used by the interpolator in the robot arm controller for forward and reverse mechanism conversion are the mechanism parameters of the ideal robot arm. Therefore, in the reverse mechanism conversion, the position setting values ​​of each motor are obtained from the set posture of the tool, which are the position setting values ​​of each motor in the ideal robot arm.

[0150] When a general machine tool or robot arm controller performs position feedback control, the tracking error is calculated from the position setting value of each motor and the measured actual motor position value. The position controller generates a motor drive value, such as a speed command, based on this tracking error. When the controller drives multiple motors to move, the actual motion trajectory will deviate from the set path, resulting in a contour error. The controller provides control and compensation methods to reduce or even eliminate tracking errors or trajectory errors, such as feed forward control (FF), trajectory control, friction compensation control, and cutting force compensation control. When implementing direct posture feedback control, it is best to retain these existing control or compensation methods in the controller.

[0151] In the direct attitude feedback control method of the present invention, in addition to the tool platform coordinate system and the basic platform coordinate system of the double ball bar attitude measurement mechanism, there are also the reference coordinates of the machine or the ideal axis coordinate system and the tool end coordinate system. There is a coordinate conversion relationship between each coordinate system, and the controller can manage these coordinate systems. When performing direct attitude feedback control, the actual attitude and attitude error of the tool can be obtained by a series of complex calculations based on the working displacement measurement values ​​of each working double ball bar in the double ball bar attitude measurement mechanism. The attitude feedback control is performed based on the attitude error. This attitude error calculation is extremely time-consuming, and the calculation time varies greatly. Arranging it in the control loop for execution will have a dead time problem, which has an adverse effect on the motor servo control.

[0152] Therefore, in the direct attitude feedback control method of the present invention, the attitude error is decomposed into a connection attitude error and a tracking attitude error. The double ball bar attitude measurement mechanism is used to measure an actual attitude of the tool. The actual position value of each motor is subtracted from the position compensation value to perform a mechanism positive conversion calculation to obtain a tool attitude, which is called the encoder defined attitude. The connection attitude error is obtained from the actual attitude and the encoder defined attitude. The attitude compensation control processes the connection attitude error to obtain the position compensation value and the compensation drive value of each motor. On the other hand, the tracking attitude error is obtained from the set attitude and the encoder defined attitude. The position feedback control processes the tracking attitude error to obtain the drive value of each motor. Since the connection attitude error changes slowly, the attitude compensation control does not need to have the same sampling time as the position feedback control.

[0153] The advantage of the direct attitude feedback control method of the present invention is that the original high sampling frequency real-time position feedback control of the controller is maintained, and a low sampling frequency attitude compensation control can be used in conjunction with the real-time position feedback control, which solves the dead time problem caused by attitude error calculation in the direct attitude feedback control, so that the direct attitude feedback control can be perfectly realized by the real-time position feedback control and attitude compensation control that run independently but cooperate with each other. The real-time position feedback control and attitude compensation control can be arranged in the same or different timer interrupt service program execution, and can have their own controllers. The sampling time of the attitude compensation control is preferably greater than or equal to the sampling time of the position feedback control. In one embodiment, the position feedback control and the attitude compensation control use the same position controller. At this time, the position compensation value of each motor obtained by the attitude compensation control can be used to correct the position setting value of each motor.

[0154] The direct attitude feedback control method derives different application methods in different machine applications. In one embodiment, the direct attitude feedback control machine is a coordinate measuring machine, and the tool installed on the tool end platform of the double-ball-bar attitude measurement mechanism is a measuring probe. The trigger signal of the measuring probe is used to synchronously latch the working displacement measurement value of each working double-ball bar in the double-ball-bar attitude measurement mechanism. After the controller reads it, it calculates the coordinate position of the center of the measuring ball at the end of the measuring probe.

[0155] In one embodiment, the basic end platform is fixed on a bracket, and the bracket is fixed on the workbench together with the workpiece. There is an offset between the basic platform coordinate system and the workpiece coordinate system. The thermal error of the bracket and the tool in the vertical direction will affect the coordinate value of the tool end point in the workpiece coordinate system. In one embodiment, the relationship between the thermal error of the bracket and the thermal error measurement value of the reference double ball bar is established, and the thermal error of the bracket height is obtained from the real-time thermal error measurement value of the reference double ball bar, and it is compensated. In one embodiment, the end point of the tool also has an offset in the tool platform coordinate system at the tool end, and the relationship between the thermal error of the tool length and the thermal error measurement value of the reference double ball bar is established. The thermal error of the tool length is obtained from the real-time thermal error measurement value of the reference double ball bar, and it is compensated.

[0156] Please refer to Figure 1 ,in Figure 1A schematic diagram of a direct attitude feedback control machine 10 according to an embodiment of the present invention is shown. The direct attitude feedback control machine 10 includes a machine body (not shown), a plurality of motors (not shown), a controller (not shown), a double ball bar attitude measurement mechanism 300, a reference plate 500 and at least one reference double ball bar 400. The machine body includes a tool end (not shown) and a base end (not shown), and the tool end is provided with a tool 6, the motor is provided on the machine body, the controller is provided outside the machine body, and the controller drives the motor to displace the tool 6 relative to a workpiece 110. The double ball bar attitude measurement mechanism 300 is provided between the base end and the tool end and includes a tool end platform 320, a base end platform 310 and at least six working double ball bars 330, the tool end platform 320 is located at the tool end; the base end platform 310 is located at the base end, and at least six working double ball bars 330 are connected to the tool end platform 320 and the base end platform 310. The reference plate 500 is not driven by a motor, and the reference plate 500 includes at least two magnetic ball sockets 510, 520, and the at least one reference double ball rod 400 is disposed on the at least two magnetic ball sockets 510, 520 of the reference plate 500. The direct attitude feedback control machine 10 may further include a spindle seat 4 and a spindle 5, the spindle seat 4 is disposed on the Z motion platform 3, the spindle 5 is connected to the spindle seat 4, and the tool end platform 320 is fixed on the spindle 5 housing.

[0157] exist Figure 1 In the embodiment, the direct attitude feedback control machine 10 may further include a workbench 12 and a base 11. The workbench 12 is located on the base 11 and can be displaced along the Y axis, and the workpiece 110 is located on the workbench 12. In order to provide direct feedback of the tool 6 relative to the workpiece 110, a double ball bar attitude measurement mechanism 300 is installed between the end of the spindle 5 and the workbench 12. The tool end platform 320 may include a plurality of ball sockets (not shown), and the base end platform 310 also includes a plurality of ball sockets (not shown). The tool end platform 320 may further include a positioning layer 321 and at least one supporting layer 322. The ball socket of the tool end platform 320 is located on the positioning layer 321 of the tool end platform 320; the base end platform 310 includes another positioning layer 311 and at least another supporting layer 312. The ball socket of the base end platform 310 is located on the positioning layer 311 of the base end platform 310. In order to reduce thermal errors, the ball socket of the base end platform 310 and the ball socket of the tool end platform 320 can be fixed on a material, and the thermal expansion coefficient of the material is between 0-1ppm / °C. Therefore, the thermal expansion coefficient of the positioning layers 311 and 321 of the fixed ball sockets can be between 0-1ppm / °C, and the thermal expansion coefficient of the support layers 312 and 322 can be between 0-2ppm / °C.

[0158] Specifically, the tool end platform 320 has a two-layer structure. The positioning layer 321 can be a hollow annular plate made of quartz with six ball sockets thereon. The supporting layer 322 is a hollow cylinder made of INVAR alloy. The end of the supporting layer 322 has a flange for supporting the positioning layer 321. The tool end platform 320 is fixed to the outer shell of the spindle 5 through the supporting layer 322. The basic end platform 310 is fixed on the workbench 12 and is also composed of a two-layer structure. The positioning layer 311 is a hollow square plate made of quartz, and the supporting layer 312 is a hollow square plate made of INVAR alloy. There are six ball sockets on the positioning layer 311. The workpiece 110 is fixed on a pad 120 in the hollow part of the basic end platform 310. Six working double ball rods 330 connect the tool end platform 320 and the basic end platform 310 to form a direct posture feedback control machine 10. The tool 6 and the workpiece 110 are in the space enclosed by the tool end platform 320, the basic end platform 310 and the six working double ball rods 330.

[0159] Tool 6 Figure 1 The example is a tool, so the direct attitude feedback control machine 10 may further include a tool length measuring device 130, which is disposed on the basic end platform 310, and the tool length measuring device 130 can be used to measure the tool length of the tool. However, in other embodiments, the tool length measuring device can also be disposed on the workbench, and is not limited thereto. In addition, the reference double ball bar 400 for thermal error compensation is placed on the reference plate 500, and the reference plate 500 is placed on the base 11.

[0160] See also Figure 2 , which shows a schematic diagram of a direct attitude feedback control machine 10a according to another embodiment of the present invention, which can perform coordinate measurement of a small-sized workpiece 110a in a general factory environment. Figure 2 In the embodiment of the invention, the direct attitude feedback control machine 10a comprises a six-axis robot arm 11a and a workbench 12a. The workbench 12a may be made of granite, and the robot arm 11a may be arranged on the workbench 12a. The tool end platform 320a is fixed on a tool mounting base (not shown) at the end of the robot arm 11a. The tool 6a is a measuring probe and is fixed on the tool end platform 320a. The basic end platform 310a is fixed on the workbench 12a. The reference plate 500a is arranged on the workbench 12a.

[0161] The basic end platform 310a has a two-layer structure. The positioning layer 311a of the basic end platform 310a is a hollow annular plate made of quartz, and the supporting layer 312a is a circular plate made of INVAR alloy. The workpiece 110a is fixed on the workpiece mounting seat 120a, and the workpiece mounting seat 120a is fixed on the supporting layer 312a. The tool end platform 320a includes a positioning layer 321a and a supporting layer 322a. Six working double ball rods 330a are connected to the tool end platform 320a and the basic end platform 310a to form a double ball rod posture measurement mechanism 300a. The tool 6a and the workpiece 110a are in the space enclosed by the tool end platform 320a, the basic end platform 310a and the six working double ball rods 330a. The reference double ball rod 400a is placed on the reference plate 500a. The tool 6a can generate a trigger signal to synchronously lock the working displacement measurement value, which is then read by the controller to calculate the center coordinate position of the measuring ball at the end of the tool 6a. Figure 2 In the embodiment of the present invention, the coordinate position of the tool 6a refers to the coordinate position of the center of the measuring ball at the end of the measuring probe. In addition, the direct attitude feedback control machine 10a may further include a reference ball 131a, which is disposed on the basic end platform 310a, and more specifically, is disposed on the support layer 312a, and is used for coordinate calibration. However, in other embodiments, the reference ball may be disposed on the workpiece mounting platform, but is not limited thereto.

[0162] See also Figure 3 , which shows another embodiment of a direct attitude feedback control machine 10b according to the present invention. Figure 3 In the embodiment of the present invention, the direct attitude feedback control machine 10b includes a six-axis robot arm 11b, a workbench 12b and a bracket 13b. The workbench 12b can be made of granite. The six-axis robot arm 11b and the bracket 13b can be arranged on the workbench 12b. The tool end can be defined as a tool mounting seat at the end of the six-axis robot arm 11b. The basic end can be defined as a basic end platform 310b mounting plane on the bracket 13b. Figure 3 In the figure, only the right half of the bracket 13b is shown to show other parts, but the present invention is not limited thereto.

[0163] exist Figure 3In the embodiment of the present invention, the basic end platform 310b of the double ball bar posture measurement mechanism 300b is installed on the bracket 13b. The basic end platform 310b has a two-layer structure. The positioning layer 311b is a ring plate made of quartz, supported by a supporting layer 312b made of INVAR alloy. The tool end platform 320b is fixed to the tool mounting seat at the end of the six-axis robot arm 11b through an adapter. The tool end platform 320b also has a two-layer structure. The positioning layer 321b is made of quartz. The annular plate is supported by a support layer 322b made of INVAR alloy. The tool 6b is a measuring probe and is fixed on the tool end platform 320b. The six working double ball rods 330b connect the tool end platform 320b and the basic end platform 310b. In this way, the tool 6b and the workpiece 110b are outside the space covered by the tool end platform 320b, the basic end platform 310b and the six working double ball rods 330b. The reference double ball rod 400b is placed on the reference plate 500b. The advantage of this direct attitude feedback control machine 10b is that the operation and access space of the workpiece 110b is larger.

[0164] In addition, in the direct attitude feedback control machine 10b, the bracket 13b is made of a material with low thermal expansion coefficient and high strength, such as INVAR alloy, which can be used in the controller 200b (shown in FIG. Figure 4 ) in which a thermal error model of the height of the bracket 13b is established, and the thermal error of the basic end platform 310b on the bracket 13b in the vertical direction is obtained based on the thermal error measurement value of the reference double ball rod 400b and compensated. The thermal error of the length of the tool 6b can also be calculated and compensated based on the thermal error measurement value. The direct attitude feedback control machine 10b may also include a reference sphere 131b, which is arranged on the workbench 12b, and the reference sphere 131b can be used for coordinate correction. It should be particularly noted here that the thermal error model of the bracket 13b can use the thermal error measured by the reference double ball rod 400b as input, so that the thermal error of the bracket 13b can be calculated from the thermal error measured by the reference double ball rod 400b. Similarly, the thermal error of the end point of the tool 6b can also be obtained. In other embodiments, the thermal error model of the bracket can also use the ambient temperature measurement value and / or the bracket temperature measurement value as input.

[0165] See also Figure 4 , and see also Figure 3 ,in Figure 4 Show Figure 3A block diagram of the control architecture of the direct attitude feedback control machine 10b of the embodiment. The controller 200b (which may be a CNC controller) of the direct attitude feedback control machine 10b includes a human-machine interface 211b operating under a window operation module 210b, and a motion control core module 220b operating in a real-time environment, which includes an interpreter 221b, an interpolator 222b, and an acceleration / deceleration planner 223b, and cooperates with a position feedback control 91 and a posture compensation control 92, which will be described later. The controller 200b uses a real-time communication network 230b. At this time, each working double ball bar 330b and the reference double ball bar 400b return each working displacement measurement value and thermal error measurement value via the real-time communication network 230b.

[0166] Specifically, the real-time communication network 230b can be an Ethernet real-time communication network (EtherCAT), and the controller 200b can communicate with the six drivers 240b and the seven digital counters 250b through the Ethernet real-time communication network, and can synchronously read the actual position value of each motor 800b, the working displacement measurement value of each working double ball rod 330b, and the thermal error measurement value of the reference double ball rod 400b, perform posture feedback control data processing, and send the driving value of each motor 800b to each corresponding driver 240b through the real-time communication network 230b. It should be particularly noted here that the displacement sensor of the working double ball rod 330b and the reference double ball rod 400b can be a laser interferometer, an optical ruler, or a magnetic ruler. In addition, each displacement sensor can be absolute or incremental, but the present invention is not limited thereto.

[0167] In the direct attitude feedback control machine 10b, the trigger signal of the tool 6b (for example, a measuring probe) can synchronously latch the working displacement measurement values ​​of the six working double ball rods 330b and the thermal error measurement values ​​of the reference double ball rods 400b. The controller 200b reads and calculates the center coordinate position of the measuring ball at the end of the tool 6b. When the tool 6b is a scanning probe, its displacement measurement signal can also be sent via the real-time communication network 230b.

[0168] In the mechanism transformation of the robot arm, the mechanism positive transformation is composed of the axis position value θ = (θ1, θ2, θ3, θ4, θ5, θ6) T , calculate the posture P in the reference coordinate system = (X, Y, Z, α, β, γ) T , where the direction can be represented by three rotation angles (α, β, γ). Assume that the position values ​​of each axis have a slight change, represented by a vector Δθ, Δθ=(Δθ1, Δθ2, Δθ3, Δθ4, Δθ5, Δθ6) T , causing a slight change in the tool posture, represented by a vector ΔP, ΔP = (ΔX, ΔY, ΔZ, Δα, Δβ, Δγ) TThe relationship between the micro-axis position change Δθ and the micro-posture change ΔP can be expressed by the Jacobian matrix J, as shown in formula (1):

[0169] ΔP=J·Δθ (1);

[0170] Conversely, the relationship between the micro-posture change ΔP and the micro-axis position change Δθ can be expressed by the Jacobian inverse matrix J -1 It is expressed as formula (2):

[0171] Δθ=J -1 ·ΔP (2).

[0172] See also Figure 5 , Figure 6 , Figure 7 , Figure 8 , Fig. 9 and Fig.10 ,in Figure 5 FIG. 1 is a block flow diagram showing attitude compensation control 92 in a direct attitude feedback control method according to the present invention. Figure 6 Show Figure 5 A schematic diagram of the posture of a tool of the direct posture feedback control method of an embodiment, Figure 7 Show Figure 5 A control flow chart of the direct attitude feedback control method of the embodiment, Figure 8 Show Figure 5 Another control flow chart of the direct attitude feedback control method of the embodiment, Fig. 9 Show Figure 5 Another control flow chart of the direct attitude feedback control method of the embodiment, Fig.10 Show Figure 5 Another control flow chart of the direct attitude feedback control method of the embodiment. Figure 7 and Figure 8 In the embodiment, the motor drive system 227d is represented by a quadratic transfer function, which includes a natural frequency ω and a damping D, and further includes an integrator 228d, the transfer function is 1 / s, which converts the velocity into displacement. The direct attitude feedback control method of the present invention includes a position feedback control 91 and an attitude compensation control 92. In this specification, the motor-related variables are represented by a numerical subscript i to represent the i-th motor, for example, θ 1，comp or θ i，comp represents the position compensation value of the first or i-th motor, with a variable without a numerical subscript such as θ comp A vector representing the position compensation values ​​for all motors.

[0173] In the direct attitude feedback control method, the attitude compensation control 92 may include an initialization step S01, a coordinate conversion relationship establishment step S02, an actual attitude calculation step S03, and a position compensation value calculation step S04. In the initialization step S01, the controller establishes the center distance function of each working double ball bar, and the coordinate conversion relationship between the tool platform coordinate system {P0} of the tool end of the double ball bar attitude measurement mechanism 300d and the basic platform coordinate system {B} of the basic end

[0174] In the coordinate transformation relationship establishment step S02, the controller establishes the coordinate transformation relationship between the basic platform coordinate system {B} and the reference coordinate system {R} according to a built-in or loaded setting value or by performing an on-board measurement. R T B .

[0175] In the actual posture calculation step S03, the controller reads the working displacement measurement values ​​of each working double ball rod and calculates the actual posture P of the tool. A .

[0176] In the position compensation value calculation step S04, the posture compensation control 92 calculates the position compensation value according to a compensation target posture and the actual posture P A , the position compensation value θ of each motor 800b is obtained comp .

[0177] Figure 7 and Figure 8 In the embodiment of the present invention, the position feedback control 91 and the attitude compensation control 92 share the position controller 911, which is based on the proportional gain value k v In this case, taking the first motor drive as an example, the posture compensation control 92 obtains the position compensation value θ 1，comp , to correct the position setting value θ of the position feedback control 91 1，s , Fig.10 In the embodiment shown in FIG. 1 , the position feedback control 91 and the attitude compensation control 92 share the position controller 911 and the control flow chart is when the transfer function is C(s). Fig. 9 In the embodiment of the present invention, the attitude compensation control 92 has its own compensation controller 921, and the transfer function is CC(s), which is composed of the position compensation value θ i，comp The compensation driving value is obtained, and the driving value obtained is added to the position controller 911, and the transfer function is C(s), and then output to the driver. In addition, the position compensation value obtained by the posture compensation control 92 is valid in the subsequent control cycle of the position feedback control 91 until the posture compensation control 92 generates a new position compensation value for updating.

[0178] Specifically, the transformation relationship between coordinate systems can be represented by a homogeneous transformation matrix T. In the initialization step S01, the mechanism parameters of the dual-ballbar attitude measurement mechanism 300d are initialized, including the center distance function of each working dual-ballbar, and the coordinate position of the center of each ball socket (i.e., ball bearing) on ​​the tool end platform and the basic end platform. In the coordinate transformation relationship establishment step S02, the controller can establish a reference coordinate system {R} through a built-in or loaded setting value, or perform on-machine measurement with the dual-ballbar attitude measurement mechanism 300d, and then establish the reference coordinate system {R}. After obtaining the reference coordinate system {R}, the controller can establish a coordinate transformation relationship between the basic platform coordinate system {B} and the reference coordinate system {R}. R T B , and after completing the initialization of the attitude compensation control, a starting reference attitude P is obtained r , and the initial position compensation value θ of each motor i，comp and compensation drive value. At this time, the tool platform coordinate system is {P0}. The double ball bar attitude measurement mechanism 300d measures the coordinate transformation relationship between the tool platform coordinate system {P0} and the basic platform coordinate system {B} Coordinate transformation relationship between tool endpoint coordinate system {T0} and tool platform coordinate system {P0} The coordinate transformation relationship between the tool end coordinate system {T0} and the basic platform coordinate system {B} is fixed. Therefore The coordinate transformation relationship between the tool end coordinate system {T0} and the reference coordinate system {R} is:

[0179] When the direct attitude feedback control machine is a three-linear axis machine, in the coordinate conversion relationship establishment step S02, the motors of the X-axis, Y-axis and Z-axis of the machine can be driven to perform positioning measurements respectively. The double-ball bar attitude measurement mechanism 300d measures multiple measurement points, and the three actual axis vectors l1, l2 and l3 of the direct attitude feedback control machine are obtained by fitting the measurement points. For example, l1 is taken as the ideal vector X, and the two vectors X and l2 are used as the outer product to establish the ideal vector Z. Then, the ideal vector Y can be established by using the outer product of Z and X. The ideal axis coordinate system of the machine can be established with these three mutually perpendicular vectors X, Y and Z. The ideal axis coordinate system can be used as the reference coordinate system {R} to obtain the coordinate conversion relationship between the actual axis coordinate system of the machine and the reference coordinate system {R}, and the coordinate conversion relationship between the basic platform coordinate system {B} and the reference coordinate system {R} R T B ,and

[0180] When the direct attitude feedback control machine is a six-axis robot arm 11d, in the coordinate transformation relationship establishment step S02, for example, the first rotary joint motor can be driven to perform positioning measurement, and multiple measurement points can be measured by the double ball bar attitude measurement mechanism 300d. The measurement points are processed to obtain a center of a circle and a normal vector of a circular plane. The ideal Z axis is the axis passing through the center of the circle and in the same direction as the normal vector. Similarly, the second rotary joint motor is driven to perform positioning measurement to obtain an actual Y axis axis vector. The actual Y axis axis vector and the ideal Z axis axis vector are used as the outer product to obtain the ideal X axis axis vector. The ideal Z axis axis vector and the ideal X axis axis vector are used as the outer product to obtain the ideal Y axis axis vector. Then, the reference coordinate system {R} of the six-axis robot arm 11d and the coordinate transformation relationship between the basic platform coordinate system {B} and the reference coordinate system {R} can be established based on the intersection of the ideal Z axis axis and the common perpendicular line with the ideal Y axis axis on the ideal Z axis axis, and the distance (nominal design value) between the ideal Y axis axis and the mounting surface of the six-axis robot arm 11d. R T B ,and

[0181] like Figure 7 As shown, the interpolator 222d of the controller may include a path interpolator 2221d and a direction interpolator 2222d. The acceleration and deceleration planner 223d plans the acceleration and deceleration, and calculates the set posture P of the tool in real time according to the input tool path and direction. S , that is, the set position (X, Y, Z) of the tool endpoint and the tool orientation, such as the three rotation angles (α, β, γ), PS = (X, Y, Z, α, β, γ) S T , and do the inverse transformation calculation of the mechanism to obtain the position setting value vector θ s =(θ 1，s ,θ 2，s ,θ 3，s ,θ 4，s ,θ 5，s ,θ 6，s ) T When the tool is fixed on the tool end platform, the coordinate transformation relationship between the tool end coordinate system {T0} and the tool platform coordinate system {P0} is is constant, so the actual tool end point coordinate system {T n} and the actual tool platform coordinate system {P n}Coordinate transformation relationship As shown in formula (1), the actual tool end point coordinate system {T n} and the coordinate transformation relationship between the reference coordinate system {R} Formula (3) and formula (4) are as follows:

[0182] and

[0183]

[0184] In formula (3), the actual tool platform coordinate system {P n} and the coordinate transformation relationship of the basic platform coordinate system {B} is measured by the double ball bar attitude measurement mechanism 300d. Through formula (3), the actual tool end point coordinate system {T n The tool position and orientation in} are converted to the reference coordinate system {R} to obtain the actual posture P A , P A =(X,Y,Z,α,β,γ,) A T . Actual tool end point coordinate system {T n The coordinate transformation relationship between} and the basic platform coordinate system {B} is: The actual tool end point coordinate system {T n The coordinate transformation relationship between} and the reference coordinate system {B} is:

[0185] By setting the posture P S The actual posture P A The actual attitude error E can be obtained a , E a =P S -P A =(ΔX, ΔY, ΔZ, Δα, Δβ, Δγ) A T Since the forward and reverse conversion calculation of the double ball bar attitude measurement mechanism 300d is complicated, and the forward and reverse conversion calculation between the coordinate systems of the robot arm also takes time, the actual attitude error E a Direct attitude feedback control will have the problem of too large dead time and unstable calculation time. In the attitude compensation control 92 of the direct attitude feedback control method of the present invention, the actual attitude error E a Disassembled, the actual position value θ of the i-th motor i，enc Subtract the position compensation value θ of the i-th motor i，comp , the encoder of the i-th motor defines the attitude position value θ i，E ,θ i，E =θ i，enc -θ i，comp , the position value θ is defined by the encoder of each motor i，E The encoder formed defines the posture position vector θ E =(θ 1，E ,θ 2，E ,θ 3，E ,θ 4，E ,θ 5，E,θ 6，E ) T , use the mechanism positive converter FKT of component number 225d to perform mechanism positive conversion, and obtain an encoder defined posture P E , P E =(X, Y, Z, α, β, γ) E T , which is the posture defined by the ideal robot arm. The encoder defines the posture P E With the actual posture P A The deviation between them is defined as a connection posture error E l , E l =P E -P A =(ΔX,ΔY,ΔZ,Δα,Δβ,Δγ) l T In the attitude compensation control of the present invention, the attitude error E is thus connected l Get the position compensation value θ of each motor i,comp , and the position compensation value vector θ comp =(θ 1comp ,θ 2,comp ,θ 3comp ,θ 4,comp ,θ 5comp ,θ 6comp ) T .

[0186] Set posture P S Define the pose P with the encoder E The difference between them is defined as the tracking attitude error E f , E f =P S -P E =(ΔX, ΔY, ΔZ, Δα, Δβ, Δγ) f T The above-mentioned setting posture P S , encoder defines the pose P E With the actual posture P A It can be obtained in the reference coordinate system {R} or in the basic platform coordinate system {B}. Tracking attitude error E f Corresponding to the axis tracking error vector Δθ in the axis coordinate system f ,

[0187] Δθ f =θ S -θ enc =(θ 1，s -θ 1，enc ,θ 2，s -θ 2，enc ,θ 3，s -θ 3，enc ,θ4，s -θ 4,enc , Δ 5,senc ,θ 6,s -θ 6,en ) T .

[0188] A main feature of the direct attitude feedback control method of the present invention is to track the attitude error E f The corresponding tracking error vector Δθ f Position feedback control 91 is performed, and the connection posture error E l Performing attitude compensation control 92 can quickly achieve complete direct attitude feedback control without dead time issues.

[0189] In the attitude compensation control 92, the target attitude can be selected for compensation according to the motion situation to obtain the position compensation value θ of each motor. i，comp . Set the value θ at each motor position i，s During the continuously changing motion, the encoders of the visual motors define the pose P E To compensate for the target posture, Figure 7 As shown, the incremental position compensation value vector Δθ comp , Δθ comp =(Δθ 1,comp ,Δθ 2,comp ,Δθ 4,comp ,Δθ 5,comp ,Δθ 6,comp ) T , can be obtained by combining the posture error E l Multiply by the Jacobian inverse matrix J of the robot arm mechanism transformation -1 It is obtained as formula (5):

[0190] Δθ comp =J -1 ×E l (5).

[0191] When the tool is set to the posture P S The position setting values ​​of each motor no longer change. At this time, the posture P can be set S To compensate the target posture, the actual posture error E a Calculate the incremental position compensation value vector Δθ comp , as shown in formula (6):

[0192] Δθ comp =J -1 ×E a (6).

[0193] See also Figure 8, which shows another control flow chart of the direct posture feedback control method. At this time, the inverse kinematic transformation (IKT) of the component number 224d performs the inverse transformation calculation, and the actual posture P of the tool is measured. A Calculate the equivalent position actual value θ of each motor i,a , the equivalent position actual value vector is θ a ,θ a =(θ 1，a ,θ 2，a ,θ 3，a ,θ 4，a ,θ 5，a ,θ 6，a ) T , and then select the compensation target posture as described above, for example Figure 8 The encoder defines the pose P E To compensate the target posture, first measure the actual position value θ of each motor from the encoder i，enc Subtract the effective position compensation value θ of each motor i，comp , the encoder defined attitude position value θ of each motor is obtained i，E ,θ i，E =θ i，enc -θ i，comp , then subtract the equivalent position actual value θi,a of each motor to obtain the new incremental position compensation value Δθ of each motor i，comp , as shown in formula (7):

[0194] Δθ i，comp =θ i，enc -θ i，comp -θ i，a , i=1..6 (7).

[0195] It should be noted that when using equations (5) and (6), the position compensation value is obtained by a first approximation method. A more accurate position compensation value can also be obtained by iterative multiple approximation methods, such as Newton's iterative approximation method, or by using actual mechanism parameters to establish a machine actual mechanism model for more accurate position compensation value calculation. This will not be repeated here. In addition, the incremental position compensation value Δθ of each motor is obtained. i，comp It is the new incremental position compensation value, so it is necessary to set up a memory to store the current valid old position compensation value, and then use the new incremental position compensation value to obtain the updated position compensation value. Figure 7 and Figure 8 In the figure, it is indicated by a time delay element TD with element number 226d. Assuming that [kT] represents the kth attitude compensation control cycle, and [kT-T] represents the k-1th attitude compensation control cycle, the update of the position compensation value of each motor is shown in formula (8):

[0196] θ i，comp [kT] = θ i，comp [kT-T]+Δθ i，comp [kT] (8);

[0197] This updated position compensation value θ i，comp [kT] Remains valid until the next update.

[0198] If the direct attitude feedback control machine is a three-linear axis machine tool, the key point of direct attitude feedback control is to drive the three linear axes to compensate for the error in the tool endpoint position. The pointing error of the tool cannot be eliminated by driving the three linear axes. However, the error in the tool endpoint position already includes the influence of the tool pointing error, namely the so-called Abbe error, which can be eliminated by direct attitude feedback control.

[0199] See also Figure 7 , Figure 8 and Fig.10 , the compensation controller 921 of the attitude compensation control 92 and the position controller 911 of the position feedback control 91 use the same controller. When the transfer function is C(s), the compensation controller 921 and the position controller 911 can be combined, such as Fig.10 As shown. Figure 7 , Figure 8 In the embodiment, C(s) is a proportional controller and the gain value is k v At this time, the motor position compensation value θ i，comp Correction position setting value θ i，s , minus the actual position value θ i，enc Then multiply by the gain value k v , that is, the drive value V after compensation of each motor is obtained cmd，i , as shown in formula (9), this driving value V cmd，i It is the speed command output by the controller to each motor driver:

[0200] V cmd，i =k v ·(θ i，s +θ i，comp -θ i，enc ) (9).

[0201] In order to avoid the influence of dead time in the direct attitude feedback control loop caused by the long calculation time of the connection attitude error, in one embodiment of the direct attitude feedback control method, a real-time timer interrupt service program first calls to execute position feedback control, and then calls to execute attitude compensation control. The position compensation value and compensation drive value of each motor calculated by the attitude compensation control are reserved for the next position feedback control cycle. In another embodiment of the direct attitude feedback control method, the compensation controller and the position controller share a proportional controller, such as Fig.10 As shown, at this time, in the kth position feedback control cycle, the motor position setting value θ i，s , the position compensation value θ calculated by the attitude compensation control in the previous position feedback control cycle (i.e., k-1 control cycles) i，comp Correction, so that in the kth control cycle, the position feedback control sends the compensated motor drive value V cmd，i [kT], due to θ c，comp [kT-T] is obtained in the previous control cycle, which does not cause the dead time problem of position feedback control, and the drive value V cmd，i [kT] is shown in formula (10):

[0202] V cmd，i [kT] = k v ·(θ i，s [kT]+θ i，comp [kT-T]-θ i，enc [kT]) (10); Alternatively, in one control cycle, the position feedback control may first obtain the drive value of each motor and then output it, and then the attitude compensation control may calculate the compensation drive value of each motor and add it to the drive value to make a secondary output.

[0203] See also Fig. 9 The position feedback control 91 has a position controller with a component number of 911 and a transfer function of C(s). The attitude compensation control 92 has a compensation controller with a component number of 921 and a transfer function of CC(s), which may be a proportional-integral-differential PID controller, for example. Fig. 9 The posture compensation control 92 shown in the figure uses an independent compensation controller 921. The advantage is that other controllers originally used in the position feedback control can be retained, such as Fig. 9 In one embodiment, the compensation controller 921 is a proportional controller, and the gain value is k vc , the position controller 911 is also a proportional controller, and the gain value is k v At this time, the compensation controller 921 uses the position compensation value θ of each motor i，comp Multiply by the gain value kvc The compensated driving value is obtained and added to the driving value obtained by the position controller 911 to obtain the compensated driving value V cmd，i , as shown in formula (11):

[0204] V cma，i =k v ·(θ i，s -θ i，cen )+k vc· θ i，comp (11).

[0205] In addition, since the static and quasi-static errors of the machine, such as geometric errors and thermal errors, change slowly, in one embodiment, the sampling time of the attitude compensation control can be much longer than the sampling time of the position feedback control to save the computational load of the central processing unit (CPU) or digital signal processor (DSP) in the controller, that is, the attitude compensation control can be arranged not to be executed in the real-time timer interrupt service program of the real-time position feedback control, but to be executed in another control cycle with a longer time interval. The sampling time or control cycle of the general position feedback control is, for example, 1 ms.

[0206] The actual posture of the tool contains all the static and dynamic behavior information of the direct posture feedback control machine, such as cutting force information when the tool is a cutter, machine axis positioning dynamic information or structural vibration information. The controller can perform signal processing analysis such as spectrum analysis on the actual posture to find out the structural vibration or motion dynamic problems of the direct posture feedback control machine. In one embodiment, the position compensation value is also processed by low-pass filtering data to obtain the position compensation value of each motor without vibration change.

[0207] See also Fig.11 ,in Fig.11The schematic diagram of a double ball bar attitude measurement mechanism 300c of a direct attitude feedback control machine according to another embodiment of the present invention is shown. The basic end platform 310c is on the top and the tool end platform 320c is on the bottom, forming an inverted double ball bar attitude measurement mechanism 300c, wherein the ball sockets P1-P6 of the tool end platform 320c and the ball sockets B1-B6 of the basic end platform 310c have an asymmetric distribution, the ball sockets B1-B6 on the basic end platform 310c are distributed in a forward semicircular range, and the ball sockets P1-P6 on the tool end platform 320c are distributed to both sides to avoid interference between the tool end platform 320c and the working double ball bar 330c and the machine body, which is beneficial for the workpiece to enter and exit from the front or horizontally, and the maximum and minimum center distances of each working double ball bar 330c are matched with the distribution of the ball sockets P1-P6 and B1-B6 of the tool end platform 320c and the ball sockets B1-B6 of the basic end platform 310c. In other words, the maximum center distance and the minimum center distance of each working double ball rod 330c are determined according to the configuration of the ball sockets P1-P6 and B1-B6.

[0208] Professionals can make other changes without departing from the spirit and key points of the present invention. For example, the driving value of each motor position feedback control includes a feedforward or trajectory error control value. The integration method of the tool end platform or the basic end platform and the machine in the double-ball bar posture measurement mechanism can have other changes. The ball socket on the tool end platform or the basic end platform can also be changed to a ball. At this time, the end of the connected working double ball bar is matched with the ball socket. The distribution of the ball socket on the tool end platform or the basic end platform can be changed according to the needs of the workspace, and the length of the working double ball bar can also be changed accordingly. The working double ball bar and the reference double ball bar can be equipped with waterproof and dustproof covers to avoid contamination. Various types of filtering processing other than spectrum analysis can also be performed on the actual posture to diagnose the dynamic behavior of the machine. After calculating the posture error, a special compensation controller can also be designed for posture compensation control.

[0209] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the appended claims.

Claims

1. A direct attitude feedback control method, applied to a direct attitude feedback control machine, the direct attitude feedback control machine comprises a controller, a double ball bar attitude measurement mechanism, a plurality of motors and a tool, the double ball bar attitude measurement mechanism is arranged between a basic end and a tool end of the direct attitude feedback control machine and comprises a tool end platform arranged on the tool end, a basic end platform arranged on the basic end, at least six working double ball bars connecting the tool end platform and the basic end platform, and at least one reference double ball bar arranged on a reference plate, the tool end platform comprises at least three ball sockets, the basic end platform comprises at least three ball sockets, the direct attitude feedback control method combines an attitude compensation control with a position feedback control, characterized in that, The attitude compensation control includes: an initialization step, causing the controller to establish a center distance function of the at least one reference double ball bar and each of the working double ball bars, and to establish a coordinate conversion relationship between a tool platform coordinate system and a basic platform coordinate system of the double ball bar posture measurement mechanism; a coordinate conversion relationship establishment step, causing the controller to establish a coordinate conversion relationship between the basic platform coordinate system and a reference coordinate system according to a built-in or loaded setting value, or an on-board measurement; an actual posture calculation step, causing the controller to read a working displacement measurement value of each working double ball rod to calculate an actual posture of the tool; as well as a position compensation value calculation step, so that the controller obtains an incremental position compensation value and a position compensation value of each motor according to a compensation target posture and the actual posture; Among them, the posture compensation control performs a mechanism positive conversion calculation by subtracting the position compensation value from the actual position value of each motor to obtain an encoder-defined posture, and obtains a connection posture error from the difference between the encoder-defined posture and the actual posture, and obtains a tracking posture error from the difference between a set posture and the encoder-defined posture. An actual posture error is obtained by the set posture and the actual posture obtained by measurement, and the position compensation value of each motor is obtained from the connection posture error or the actual posture error. The posture compensation control uses a compensation controller for each motor, and the compensation controller generates a compensated drive value for each motor from the position compensation value of each motor. The position feedback control uses a position controller for each motor, and obtains a drive value from the difference between a position setting value and the actual position value. The drive value is added to the compensated drive value and output to a driver of each motor. The position compensation value of each motor remains valid until the posture compensation control is updated.

2. The direct attitude feedback control method according to claim 1, characterized in that: A sampling time of the posture compensation control is greater than or equal to a sampling time of the position feedback control.

3. The direct attitude feedback control method according to claim 1, characterized in that: The compensation target posture is the encoder defined posture or the set posture.

4. The direct attitude feedback control method according to claim 1, characterized in that: The incremental position compensation value of each motor is obtained by using an inverse Jacobian matrix.

5. The direct attitude feedback control method according to claim 1, characterized in that: The incremental position compensation value of each motor is obtained by subtracting an equivalent position actual value of each motor from an encoder-defined posture position value of each motor.

6. The direct attitude feedback control method according to claim 1, characterized in that: The compensation controller is a proportional controller.

7. The direct attitude feedback control method according to claim 1, characterized in that: The compensation controller of each motor is the same as the position controller. At this time, the position compensation value of each motor is added to the position setting value of each motor and then input into the position controller to obtain a compensated driving value.

8. The direct attitude feedback control method according to claim 1, characterized in that: The position compensation value of each motor is subjected to low-pass filtering to obtain the position compensation value without vibration factors.

9. The direct attitude feedback control method according to claim 1, characterized in that: In the initialization step, at least one of the motors is driven to make each of the working double ball bars pass through an origin to initialize the center distance function of each of the working double ball bars built into or loaded into the controller.

10. The direct attitude feedback control method according to claim 1, characterized in that: The on-board measurements include: At least two of the motors are driven to position respectively, the reference coordinate system is obtained from the measurement results of the double-ball-bar attitude measurement mechanism, and the coordinate conversion relationship between the basic platform coordinate system and the reference coordinate system is obtained.

11. The direct attitude feedback control method according to claim 1, characterized in that: In the position compensation value calculation step, a single approximation method or an iterative multiple approximation method is used to calculate the incremental position compensation value of each motor.

12. The direct attitude feedback control method according to claim 1, characterized in that: The controller reads in a thermal error measurement value of the reference double ball bar, calculates and compensates for a thermal error of each mechanism parameter of the double ball bar posture measurement mechanism based on the thermal error measurement value, including the thermal error of the ball socket position on the tool end platform and the basic end platform and the thermal error of the center distance of the working double ball bar.

13. The direct attitude feedback control method according to claim 1, characterized in that: In the actual posture calculation step, the controller reads out each of the working displacement measurement values ​​synchronously latched by a trigger signal, and calculates a coordinate position of the center of a measuring ball at the end of the tool.

14. The direct attitude feedback control method according to claim 12, characterized in that: The direct attitude feedback control machine further comprises a bracket for mounting the basic end platform, and in the actual attitude calculation step, a thermal error of the bracket height is calculated and compensated according to the thermal error measurement value of the reference double ball bar.

15. The direct attitude feedback control method according to claim 12, characterized in that: In the actual posture calculation step, a thermal error of the tool length is calculated and compensated according to the thermal error measurement value of the reference double ball bar.

16. The direct attitude feedback control method according to claim 1, characterized in that: The controller performs a spectrum analysis on the actual posture to obtain vibration information of the direct posture feedback control machine.

17. A direct attitude feedback control machine, characterized in that: Include: A machine body, comprising a tool end and a base end, wherein the tool end is provided with a tool; A plurality of motors are disposed on the machine body; a controller that drives the motor to move the tool relative to a workpiece at the base end; and A double-club posture measuring mechanism is disposed between the base end and the tool end and comprises: a tool end platform located at the tool end and including at least three ball sockets; a base end platform located at the base end and including at least three ball sockets; At least six working double ball rods are connected between the ball socket of the tool end platform and the ball socket of the basic end platform, each of the working double ball rods comprises two measuring balls, and a displacement sensor of each working double ball rod is used to measure the distance between the centers of the two measuring balls; a reference plate comprising at least two reference sockets; and At least one reference double ball bar, including two reference measuring balls, disposed between the at least two reference ball sockets of the reference plate, and a displacement sensor is used to measure the distance between the centers of the two reference measuring balls; Among them, the controller uses the reference double ball bar as a measuring device for the thermal error of the mechanical parameters of the double ball bar posture measurement mechanism, and uses the double ball bar posture measurement mechanism as a measuring device for an actual posture of the tool. The controller has a posture compensation control, and a connection posture error is obtained by the difference between a posture defined by an encoder and the actual posture, and a tracking posture error is obtained by the difference between a set posture and the posture defined by the encoder. A position compensation value and a compensated drive value of each motor are obtained from the connection posture error. The compensated drive value is added to a drive value obtained by a position controller of each motor and output to a driver of each motor.

18. The direct attitude feedback control machine of claim 17, wherein: Also includes: A spindle seat, disposed on the machine body; and A spindle connected to the spindle seat and comprising a spindle housing; Wherein, the tool end platform is fixed on the spindle seat or the spindle housing.

19. The direct attitude feedback control machine of claim 17, wherein: The direct attitude feedback control machine is a multi-axis machine tool, a multi-axis joint machine or a parallel linkage drive machine.

20. The direct attitude feedback control machine of claim 17, wherein: The tool is a tool, a measuring probe, a trigger probe, a conjugate focusing sensor, a displacement measuring laser or an optical measuring lens.

21. The direct attitude feedback control machine of claim 17, wherein: The tool generates a trigger signal, and uses the trigger signal to synchronously lock a working displacement measurement value of each working double ball rod.

22. The direct attitude feedback control machine of claim 17, wherein: Also includes: A reference ball is arranged on the basic end platform or a workbench.

23. The direct attitude feedback control machine of claim 17, wherein: Also includes: A knife length measuring mechanism is arranged on the basic end platform or a workbench.

24. The direct attitude feedback control machine of claim 17, wherein: The ball socket on the tool end platform and the ball socket on the basic end platform have an asymmetric distribution.

25. The direct attitude feedback control machine of claim 17, wherein: The ball sockets on the base end platform and the tool end platform are fixed on a material with a thermal expansion coefficient between 0 ppm / °C and 2 ppm / °C.

26. The direct attitude feedback control machine of claim 17, wherein: It also includes a bracket, and the basic end platform is installed on the bracket.

27. The direct attitude feedback control machine of claim 17, wherein: The controller comprises a real-time communication network, through which each of the working double-ball rods and the reference double-ball rod transmits back a working displacement measurement value of each of the working double-ball rods and a thermal error measurement value of the reference double-ball rod.

28. The direct attitude feedback control machine of claim 27, wherein: The real-time communication network is a real-time Ethernet communication network.

29. The direct attitude feedback control machine of claim 17, wherein: The displacement sensor of each of the working double ball bars and the reference double ball bar is a laser interferometer, an optical ruler or a magnetic ruler.

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