CN111716331A - Six-degree-of-freedom parallel mechanism parameter calibration device and method - Google Patents
Six-degree-of-freedom parallel mechanism parameter calibration device and method Download PDFInfo
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- CN111716331A CN111716331A CN202010595602.1A CN202010595602A CN111716331A CN 111716331 A CN111716331 A CN 111716331A CN 202010595602 A CN202010595602 A CN 202010595602A CN 111716331 A CN111716331 A CN 111716331A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
- B25J9/00—Programme-controlled manipulators
- B25J9/003—Programme-controlled manipulators having parallel kinematics
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
- B25J13/00—Controls for manipulators
- B25J13/08—Controls for manipulators by means of sensing devices, e.g. viewing or touching devices
- B25J13/088—Controls for manipulators by means of sensing devices, e.g. viewing or touching devices with position, velocity or acceleration sensors
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
- B25J9/00—Programme-controlled manipulators
- B25J9/16—Programme controls
- B25J9/1602—Programme controls characterised by the control system, structure, architecture
Abstract
The invention relates to a parameter calibration device and a parameter calibration method for a six-degree-of-freedom parallel mechanism, wherein the parameter calibration device comprises a displacement sensor, a sensor seat, a measured reference block, a support and a parameter calibration calculation module; the sensor seat comprises three mutually orthogonal planes, 1,2 and 3 displacement sensors are respectively fixed on the three planes, the axis of a measuring rod of each displacement sensor is vertical to the corresponding plane, and the sensor seat is fixed on a fixed platform of the six-degree-of-freedom parallel mechanism through a support; the measured reference block comprises three mutually orthogonal reference planes which correspond to the three planes one by one, contacts of the displacement sensor are contacted with the corresponding reference planes, and the measured reference block is fixed at the top of the movable platform of the six-degree-of-freedom parallel mechanism; and the parameter calibration calculation module calibrates and compensates the parameters of the six-degree-of-freedom parallel mechanism. The parameter calibration device for the six-degree-of-freedom parallel mechanism has the advantages of low cost, simplicity in operation, time and labor saving, high calibration efficiency and the like.
Description
Technical Field
The invention relates to the technical field of mechanics, in particular to a six-degree-of-freedom parallel mechanism parameter calibration device and method.
Background
The six-degree-of-freedom parallel mechanism has the advantages of high precision, high rigidity, no accumulated error and the like, and is widely applied to the fields of fine adjustment, ultra-precision machining and the like of optical elements.
Due to the existence of processing and assembling errors, certain deviation exists between the actual structural parameters and the theoretical structural parameters of the six-degree-of-freedom parallel mechanism, so that certain deviation exists between a kinematic model established according to the theoretical parameters and an actual structure. The machining error of the structural part can be reduced by adopting a high-precision machine tool, but the cost is high, and the error is compensated by parameter calibration, so that the method is low in cost and effective.
In the calibration process of the six-degree-of-freedom parallel mechanism, the pose of the six-degree-of-freedom parallel mechanism needs to be measured. At present, three-coordinate measuring machines, measuring arms, laser trackers, laser interferometers and other equipment are mostly adopted for pose measurement, and although the equipment has the characteristics of high precision, wide adaptability and the like, the equipment is expensive in manufacturing cost, time-consuming and labor-consuming in operation, high in operation requirement and inconvenient in application, so that the calibration efficiency is low, and particularly, the parallel mechanism with a large working space is more obvious. Some poses of the moving platform may not be measured due to space limitations, and satisfactory measurement data is difficult to obtain when the moving platform changes poses within a large working space. Therefore, it is necessary to consider other simple and efficient pose measurement means and improve the calibration efficiency.
Disclosure of Invention
Therefore, it is necessary to provide a simple and efficient parameter calibration device and method for a six-degree-of-freedom parallel mechanism to solve the problems of high cost, time and labor consuming operation, low calibration efficiency, low calibration precision and the like of the calibration method for the six-degree-of-freedom parallel mechanism in the prior art, so as to achieve the purposes of reducing cost, simplifying calibration process and improving calibration efficiency.
In order to achieve the purpose, the invention adopts the following technical scheme:
a parameter calibration device for a six-degree-of-freedom parallel mechanism comprises a displacement sensor, a sensor seat, a measured reference block, a support and a parameter calibration calculation module;
the sensor seat comprises three mutually orthogonal planes, 1,2 and 3 displacement sensors are respectively fixed on the three planes, the axes of measuring rods of the displacement sensors are vertical to the corresponding planes, and the sensor seat is fixed on a fixed platform of a six-degree-of-freedom parallel mechanism through the bracket;
the measured reference block comprises three mutually orthogonal reference planes which correspond to the three planes one by one, contacts of the displacement sensor are in contact with the corresponding reference planes, and the measured reference block is fixed at the top of the movable platform of the six-degree-of-freedom parallel mechanism;
the parameter calibration calculation module acquires actual values of the expansion amount of each displacement sensor when the six-degree-of-freedom parallel mechanism is in different poses, determines the optimal structure parameter error of the six-degree-of-freedom parallel mechanism according to the actual values of the expansion amount, and calibrates and compensates the parameters of the six-degree-of-freedom parallel mechanism according to the optimal structure parameter error.
The invention also provides a parameter calibration method based on the six-degree-of-freedom parallel mechanism parameter calibration device, wherein the parameter calibration calculation module is used for executing the parameter calibration method, and the parameter calibration method comprises the following steps:
the method comprises the following steps: presetting an initial value of a structural parameter of the six-degree-of-freedom parallel mechanism, and adding a corresponding structural parameter error to the structural parameter of the six-degree-of-freedom parallel mechanism;
step two: presetting an initial value of a structural parameter of the six-degree-of-freedom parallel mechanism parameter calibration device, and adding a corresponding structural parameter error to the structural parameter of the six-degree-of-freedom parallel mechanism parameter calibration device;
step three: presetting nominal poses of a movable platform of a six-degree-of-freedom parallel mechanism, wherein the number of the nominal poses is greater than or equal to a lower limit value;
step four: calculating the nominal value of the expansion amount of each displacement sensor under each nominal pose;
step five: driving a six-degree-of-freedom parallel mechanism by using a controller to enable the movable platform to move to each nominal pose, and recording the actual value of the expansion amount of each displacement sensor under each nominal pose;
step six: the actual value of the expansion amount of each displacement sensor under each nominal pose is subtracted from the nominal value of the expansion amount to obtain an indication value error of each displacement sensor under each nominal pose;
step seven: constructing a mathematical model of an optimization problem by taking the minimum sum of squares of indication errors of all the displacement sensors as an objective function and taking structural parameter errors of the six-degree-of-freedom parallel mechanism and the six-degree-of-freedom parallel mechanism parameter calibration device as design variables;
step eight: searching out the optimal solution of the mathematical model by using advanced optimization software;
step nine: and substituting the optimal solution obtained by searching into a mathematical model of the six-degree-of-freedom parallel mechanism to realize parameter calibration and compensation of the six-degree-of-freedom parallel mechanism.
Compared with the prior art, the invention has the following beneficial effects:
1) low cost
The six-degree-of-freedom parallel mechanism parameter calibration device mainly comprises the following components: compared with expensive instruments such as a three-coordinate measuring machine, a laser tracker and the like, the six high-precision displacement sensors, the measured reference block and the sensor seat have extremely low cost;
2) simple operation
Before calibration, parameter calibration can be carried out only by fixing a measured reference block on a movable platform of the six-degree-of-freedom parallel mechanism, fixing a displacement sensor on a sensor seat and fixing the sensor seat on a fixed platform of the six-degree-of-freedom parallel mechanism through a support; during calibration, only the controller of the six-degree-of-freedom parallel mechanism needs to be operated, and a parameter calibration device of the six-degree-of-freedom parallel mechanism does not need to be operated, so that the whole calibration process is simple to operate, and time and labor are saved;
3) high calibration efficiency
As long as the end pose of the six-degree-of-freedom parallel mechanism is changed, the measured value of the displacement sensor, namely the actual value of the stretching amount, can be instantly obtained, the pose does not need to be solved, the actual value of the stretching amount of the displacement sensor is subtracted from the nominal value of the stretching amount, the difference is substituted into advanced optimization software, the optimal structure parameter error of the six-degree-of-freedom parallel mechanism can be calculated in a short time, and the parameter calibration efficiency is greatly improved.
Drawings
FIG. 1 is a schematic structural diagram of a parameter calibration apparatus for a six-degree-of-freedom parallel mechanism according to an embodiment of the present invention;
FIG. 2 is a schematic structural view of the sensor mount and bracket of FIG. 1 shown without the sensor mount and bracket;
FIG. 3 is a schematic view of the displacement sensor of FIG. 1 in relation to the sensor receptacle;
FIG. 4 is a schematic diagram of the relationship between the displacement sensor and the reference block to be measured in FIG. 1;
FIG. 5 is a schematic flow chart illustrating a method for calibrating parameters of a six-degree-of-freedom parallel mechanism according to an embodiment of the present invention.
Detailed Description
The technical solution of the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments.
In one embodiment, as shown in fig. 1 to 4, the present invention discloses a parameter calibration apparatus for a six-degree-of-freedom parallel mechanism, which mainly comprises: the six displacement sensors are respectively a displacement sensor 1-a displacement sensor 6, a sensor seat 7, a measured reference block 8, a support 9 and a parameter calibration calculation module.
Specifically, the sensor seat 7 comprises three mutually orthogonal planes which are a plane 7-1, a plane 7-2 and a plane 7-3 respectively, the plane 7-1 is fixedly provided with the displacement sensor 1, the displacement sensor 2 and the displacement sensor 3, the plane 7-2 is fixedly provided with the displacement sensor 4 and the displacement sensor 5, the plane 7-3 is fixedly provided with the displacement sensor 6, and the axes of measuring rods of the displacement sensor 1 to the displacement sensor 6 are vertical to the corresponding planes. The sensor seat 7 is fixed on a fixed platform 10 of the six-degree-of-freedom parallel mechanism through a support 9, and the sensor seat 7 and the support 9 are not in contact with a movable platform 11 of the six-degree-of-freedom parallel mechanism.
Preferably, the displacement sensor in this embodiment is a grating displacement sensor, which has the characteristics of large detection range, high detection precision and fast response speed, for example, a czech ESSA grating displacement sensor SM30 series may be used.
Optionally, the sensor seat 7 is a hollow cuboid or cube with an open bottom, and the inner hollow of the cuboid or cube is used for accommodating the measured reference block 8.
The measured reference block 8 comprises three mutually orthogonal reference planes which are respectively in one-to-one correspondence with the planes 7-1, 7-2 and 7-3 and are respectively a reference plane 8-1, a reference plane 8-2 and a reference plane 8-3, and the contacts of the displacement sensors are in contact with the corresponding reference planes, namely the contacts of the displacement sensors 1,2 and 3 are in contact with the reference plane 8-1 of the measured reference block 8, the contacts of the displacement sensors 4 and 5 are in contact with the reference plane 8-2 of the measured reference block 8, and the contact of the displacement sensor 6 is in contact with the reference plane 8-3 of the measured reference block 8. The measured reference block 8 is fixed on the top of a movable platform 11 of the six-degree-of-freedom parallel mechanism.
Optionally, the measured reference block 8 is a cuboid or a cube, and the measured reference block 8 may have a solid structure or a hollow structure, which is not limited herein.
Optionally, the sensor seat 7 and the measured reference block 8 are made of cast iron, and the bracket 9 is made of 45 # steel, so that the sensor seat has the advantages of high strength, difficulty in deformation and the like.
The parameter calibration calculation module acquires the actual values of the stretching amounts of the displacement sensors when the six-degree-of-freedom parallel mechanism is in different poses, determines the optimal structure parameter error of the six-degree-of-freedom parallel mechanism according to the actual values of the stretching amounts, and calibrates and compensates the parameters of the six-degree-of-freedom parallel mechanism according to the optimal structure parameter error.
The parameter calibration device for the six-degree-of-freedom parallel mechanism provided by the embodiment has the advantages of low cost, simplicity in operation, time and labor saving, high calibration efficiency and the like.
In another embodiment, the present invention provides a method for calibrating parameters of a six-degree-of-freedom parallel mechanism, which is implemented based on the parameter calibration apparatus of a six-degree-of-freedom parallel mechanism described in the foregoing embodiment, and the structure of the parameter calibration apparatus of a six-degree-of-freedom parallel mechanism is referred to the foregoing embodiment and is not described herein again. The parameter calibration calculation module is used for executing the parameter calibration method of the six-degree-of-freedom parallel mechanism in the embodiment, and specifically, the parameter calibration method comprises the following steps:
step one (S100): the initial value of the structural parameter of the six-degree-of-freedom parallel mechanism is preset, and the corresponding structural parameter error is added to the structural parameter of the six-degree-of-freedom parallel mechanism.
The structural parameters of the six-degree-of-freedom parallel mechanism comprise coordinates of six hinge points on a fixed platform of the six-degree-of-freedom parallel mechanism under a fixed platform coordinate system, coordinates of six hinge points on a movable platform under a movable platform coordinate system and lengths of six branched chains. Specifically, the number of the structural parameters of the six-degree-of-freedom parallel mechanism is 42 in total, and the structural parameters are X respectivelyBi,YBi,ZBi,li,XPi,YPi,ZPi(i ═ 1,2,3,4,5,6), where:
(1)[XBiYBiZBi]＝[nXBi nYBi nZBi]+[ΔXBiΔYBiΔZBi]is the coordinate of the ith hinge point on the fixed platform of the six-freedom parallel mechanism in the fixed platform coordinate system (hereinafter referred to as fixed system)nXBi nYBi nZBi]To determine the nominal value of the coordinates of the ith hinge point of the platform, the upper left corner n is the abbreviation for "nominal" (nominal) (the same applies hereinafter), [ Δ X [ ]BiΔYBiΔZBi]The coordinate error of the ith hinge point of the fixed platform is determined;
(2)[XPiYPiZPi]＝[nXPi nYPi nZPi]+[ΔXPiΔYPiΔZPi]is the coordinate of the ith hinge point on the moving platform of the six-freedom parallel mechanism in the moving platform coordinate system (hereinafter referred to as the moving system)nXPi nYPi nZPi]Is the coordinate nominal value of the ith hinge point of the movable platform, [ Delta X ]PiΔYPiΔZPi]The coordinate error of the ith hinge point of the movable platform is obtained;
(3)li＝nli+Δliis the length of the ith branched chain of the six-degree-of-freedom parallel mechanism,nliis a nominal value of the length of the ith branch,. DELTA.liThe length error of the ith branch is shown.
Step two (S200): presetting an initial value of the structural parameter of the six-degree-of-freedom parallel mechanism parameter calibration device, and adding a corresponding structural parameter error for the structural parameter of the six-degree-of-freedom parallel mechanism parameter calibration device.
Optionally, the step two of presetting the initial value of the structural parameter of the six-degree-of-freedom parallel mechanism parameter calibration device comprises the following steps of:
step two, firstly: and constructing a coordinate system of the measured reference block.
Firstly, a parameter calibration device of a six-degree-of-freedom parallel mechanism is modeled. The intersection point of three planes of a measured reference block 8 is abstracted as the origin of a measured reference block coordinate system (hereinafter, referred to as a reference block system), a reference plane 8-1 is abstracted as an XOY plane of the reference block system and is abbreviated as an 'I plane', the intersection line of the reference plane 8-1 and a reference plane 8-2 is abstracted as an X axis, a plane passing through the X axis and perpendicular to the reference plane 8-1 is defined as an XOZ plane and is abbreviated as a 'II plane', and a plane passing through the origin and perpendicular to the X axis is defined as a YOZ plane and is abbreviated as a 'III plane'. And constructing a coordinate system of the measured reference block. The displacement sensors 1 to 6 are abstracted into spatial straight lines S1 to S6, wherein the intersections of the straight lines S1, S2 and S3 with the I plane are defined as M1, M2 and M3, the intersections of the straight lines S4 and S5 with the II plane are defined as M4 and M5, and the intersection of the straight line S6 with the III plane is defined as M6.
Step two: presetting the pose of the coordinate system of the measured reference block under the six-freedom-degree parallel mechanism dynamic system.
The pose of the preset reference block system under the six-freedom-degree parallel mechanism dynamic system is as follows:
in the formula:
Writing equation (1) as a homogeneous coordinate transformation is:
in the formula, c represents cos and s represents sin.
Step two and step three: and presetting the pose of the measured reference block under the fixed platform coordinate system of the six-degree-of-freedom parallel mechanism when the movable platform coordinate system is at the zero position to obtain expressions of an XOY surface, an XOZ surface and a YOZ surface of the measured reference block when the movable platform coordinate system is at the zero position.
In this step, the pose of the reference block system under the fixed system of the six-degree-of-freedom parallel mechanism when the preset dynamic system is at the zero position is expressed by an RPY angle:
in the formula:
Writing equation (3) as a homogeneous coordinate transformation form:
in the formula, c represents cos and s represents sin.
An expression of the I surface of the measured reference block when the dynamic system is at the zero position can be obtained according to the formula (4):
in the formula (I), the compound is shown in the specification,
is a point on the I surface, namely the coordinate origin of the reference block system,
and
is a vector in the I plane.
And when the dynamic system is at a zero position, the expression of the II surface of the measured reference block is as follows:
in the formula (I), the compound is shown in the specification,
is a point on the surface II of the wafer,
and
is a vector in the plane II.
And the expression of the III surface of the measured reference block when the dynamic system is at the zero position:
in the formula (I), the compound is shown in the specification,
is a point on the plane III of the wafer,
and
is a vector in plane III.
Step two, four: and presetting expressions of straight lines where the displacement sensors are located.
Presetting linear expressions of the displacement sensors 1 to 6:
Lk＝[xkykzkdxkdykdzk],k＝1,2,3,4,5,6 (8)
in the formula:
[xkykzk]＝[nxk nyk nzk]+[ΔxkΔykΔzk]represents a point coordinate on a straight linenxk nyk nzk]Is a nominal value of the coordinates of a point on a straight line, [ Δ x ]kΔykΔzk]Is the coordinate error of a point on the straight line;
[dxkdykdzk]＝[ndxk ndyk ndzk]+[ΔdxkΔdykΔdzk]a vector [ alpha ] representing a straight linendxk ndyk ndzk]Is the nominal value of the vector of the straight line, [ Δ dx ]kΔdykΔdzk]Is the vector error of the straight line.
And presetting the structural parameters of the parameter calibration device of the six-degree-of-freedom parallel mechanism through the first step to the second step, wherein the total number of the structural parameters is 48.
Step three (S300): the nominal poses of the movable platform of the six-degree-of-freedom parallel mechanism are preset, and the number of the nominal poses is larger than or equal to a lower limit value.
The nominal poses of a movable platform of a preset six-degree-of-freedom parallel mechanism are as follows:
in the formula (I), the compound is shown in the specification,
is the coordinate of the coordinate origin of the motion system in the fixed system under the j-th nominal pose,
and j is equal to or more than m, m is a lower limit value of the number of the nominal poses, and optionally, m is 15.
Step four (S400): and calculating the nominal value of the expansion amount of each displacement sensor under each nominal pose.
Optionally, the step four of calculating the nominal value of the expansion amount of each displacement sensor in each nominal pose includes the following steps:
step four, firstly: and calculating the zero position coordinates of the contact points of the displacement sensors and the corresponding coordinate plane in the reference block system in the fixed system when the dynamic system is in the zero position. When equations (5), (6), (7), and (8) are combined, the coordinates of the contact point can be obtained and are recorded as:
in the formula (I), the compound is shown in the specification,
the coordinate of the displacement sensor k and the contact of the corresponding coordinate plane in the reference block system in the fixed system when the moving system is at the zero position is the zero position coordinate.
Step four and step two: and calculating the position and attitude coordinates of each displacement sensor and the contact of the corresponding coordinate plane in the reference block system in the fixed system when the dynamic system is in the nominal position and attitude.
And according to the first step, the third step, expressions of homogeneous coordinate transformation of different nominal poses and plane expressions of a coordinate plane I, a plane II and a plane III under different nominal poses can be deduced. The linear expression of the displacement sensor is combined with the plane expressions of the coordinate planes I, II and III under different nominal poses, so that the coordinates of the contact points of each displacement sensor and each corresponding coordinate plane in the reference block system can be solved and recorded as:
in the formula (I), the compound is shown in the specification,
the coordinates of the displacement sensor k of the motion system in each position and the contact of the corresponding coordinate plane in the reference block system in the fixed system are the position coordinates.
Step four and step three: and calculating the linear distance between two contacts of each displacement sensor under each nominal pose according to the zero position coordinates and the pose coordinates to obtain the nominal value of the expansion amount of each displacement sensor under each nominal pose.
Calculating the linear distance between two contact points of each displacement sensor when the dynamic system is at a zero position and the dynamic system is at a nominal pose according to the formula (10) and the formula (11):
when the contact when the dynamic system is in the nominal pose moves to the reference axis in the positive direction relative to the contact when the dynamic system is in the zero position, the nominal value of the expansion amount of the displacement sensor is regulated to be positive, namely
hk|＝hk| (13)
When the contact when the dynamic system is in the nominal pose moves towards the negative direction of the reference shaft relative to the contact when the dynamic system is in the zero position, the nominal value of the expansion amount of the specified displacement sensor is negative, namely
hk＝-|hk| (14)
The reference axis is a coordinate axis parallel to a normal of a coordinate plane corresponding to the displacement sensor in the reference block system.
Therefore, the nominal value of the expansion amount of each displacement sensor under each nominal pose is calculated and recorded as:
nHj＝[nhj1 nhj2 nhj3 nhj4 nhj5 nhj6](15)
in the formula (I), the compound is shown in the specification,nhj1，nhj2，nhj3，nhj4，nhj5，nhj6respectively, the nominal values of the expansion and contraction amounts of the 6 displacement sensors.
Step five (S500): and driving the six-degree-of-freedom parallel mechanism by using the controller to enable the movable platform to move to each nominal pose, and recording the actual expansion value of each displacement sensor under each nominal pose.
The controller is used for driving the six-degree-of-freedom parallel mechanism to enable the movable platform to move to nominal poses in sequence, the displacement sensor is used for measuring actual values of the stretching amount under different nominal poses, and the measurement result of each nominal pose is recorded as:
aHj＝[ahj1 ahj2 ahj3 ahj4 ahj5 ahj6](16)
in the formula (I), the compound is shown in the specification,ahj1，ahj2，ahj3，ahj4，ahj5，ahj6nominal values for the amount of expansion and contraction of 6 displacement sensors, respectively, and the upper left-hand symbol a is an abbreviation for "actual".
Step six (S600): and (3) subtracting the actual value of the stretching amount of each displacement sensor under each nominal pose from the nominal value of the stretching amount to obtain the indicating value error of each displacement sensor under each nominal pose, and recording the indicating value error of each displacement sensor under each nominal pose as follows:
ΔHj＝[Δhj1Δhj2Δhj3Δhj4Δhj5Δhj6](17)
in the formula,. DELTA.hj1，Δhj2，Δhj3，Δhj4，Δhj5，Δhj6The difference values of the nominal value and the actual value of the stretching amount of the 6 displacement sensors are respectively.
Step seven (S700): and constructing a mathematical model of the optimization problem by taking the minimum sum of squares of indicating value errors of all displacement sensors as an objective function and taking structural parameter errors of the six-degree-of-freedom parallel mechanism and the six-degree-of-freedom parallel mechanism parameter calibration device as design variables.
In this step, a mathematical model of the optimization problem is constructed. With the least square sum of the indication errors of all displacement sensors as the objective function, i.e.
In the formula, m is the number of nominal poses.
Taking the structure parameter error of the six-freedom-degree parallel mechanism and the six-freedom-degree parallel mechanism parameter calibration device as a design variable, namely
The constraint condition of the variable is the value range of the variable under the existing processing and assembling capability, and the error of the endpoint of the value range is plus or minus 0.1 (mm).
Step eight (S800): and searching out the optimal solution of the mathematical model by using advanced optimization software. The advanced optimization software in the invention can be realized by software in the prior art, for example, OASIS software is adopted, and the OASIS software realizes the optimal solution search of the mathematical model based on an advanced optimization algorithm to obtain the optimal solution of the mathematical model, namely the optimal structure parameter error.
Step nine (S900): and substituting the optimal solution obtained by searching into a mathematical model in control software of the six-degree-of-freedom parallel mechanism to realize parameter calibration and compensation of the six-degree-of-freedom parallel mechanism.
The parameter calibration device, namely the method for the six-degree-of-freedom parallel mechanism provided by the embodiment of the invention has the following beneficial effects:
1) low cost
The six-degree-of-freedom parallel mechanism parameter calibration device mainly comprises the following components: compared with expensive instruments such as a three-coordinate measuring machine, a laser tracker and the like, the six high-precision displacement sensors, the measured reference block and the sensor seat have extremely low cost;
2) simple operation
Before calibration, parameter calibration can be carried out only by fixing a measured reference block on a movable platform of the six-degree-of-freedom parallel mechanism, fixing a displacement sensor on a sensor seat and fixing the sensor seat on a fixed platform of the six-degree-of-freedom parallel mechanism through a support; during calibration, only the controller of the six-degree-of-freedom parallel mechanism needs to be operated, and a parameter calibration device of the six-degree-of-freedom parallel mechanism does not need to be operated, so that the whole calibration process is simple to operate, and time and labor are saved;
3) high calibration efficiency
As long as the end pose of the six-degree-of-freedom parallel mechanism is changed, the measured value of the displacement sensor, namely the actual value of the stretching amount, can be instantly obtained, the pose does not need to be solved, the actual value of the stretching amount of the displacement sensor is subtracted from the nominal value of the stretching amount, the difference is substituted into advanced optimization software, the optimal structure parameter error of the six-degree-of-freedom parallel mechanism can be calculated in a short time, and the parameter calibration efficiency is greatly improved.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A parameter calibration device of a six-degree-of-freedom parallel mechanism is characterized by comprising a displacement sensor, a sensor seat (7), a measured reference block (8), a support (9) and a parameter calibration calculation module;
the sensor seat (7) comprises three mutually orthogonal planes, 1,2 and 3 displacement sensors are respectively fixed on the three planes, the axes of measuring rods of the displacement sensors are vertical to the corresponding planes, and the sensor seat (7) is fixed on a fixed platform (10) of the six-degree-of-freedom parallel mechanism through the bracket (9);
the measured reference block (8) comprises three mutually orthogonal reference planes which correspond to the three planes one by one, contacts of the displacement sensor are all contacted with the corresponding reference planes, and the measured reference block (8) is fixed at the top of a movable platform (11) of the six-degree-of-freedom parallel mechanism;
the parameter calibration calculation module acquires actual values of the expansion amount of each displacement sensor when the six-degree-of-freedom parallel mechanism is in different poses, determines the optimal structure parameter error of the six-degree-of-freedom parallel mechanism according to the actual values of the expansion amount, and calibrates and compensates the parameters of the six-degree-of-freedom parallel mechanism according to the optimal structure parameter error.
2. The six-degree-of-freedom parallel mechanism parameter calibration device according to claim 1,
the displacement sensor adopts a grating displacement sensor.
3. The six-degree-of-freedom parallel mechanism parameter calibration device according to claim 1 or 2,
the sensor seat (7) and the measured reference block (8) are made of cast iron materials, and the support (9) is made of 45-grade steel.
4. The six-degree-of-freedom parallel mechanism parameter calibration device according to claim 1 or 2,
the sensor seat (7) is a hollow cuboid or cube with an opening at the bottom.
5. The six-degree-of-freedom parallel mechanism parameter calibration device according to claim 1 or 2,
the measured reference block (8) is a cuboid or a cube.
6. A parameter calibration method based on the parameter calibration device of the six-degree-of-freedom parallel mechanism according to any one of claims 1 to 5, wherein the parameter calibration calculation module is used for executing the parameter calibration method, and the parameter calibration method comprises the following steps:
the method comprises the following steps: presetting an initial value of a structural parameter of the six-degree-of-freedom parallel mechanism, and adding a corresponding structural parameter error to the structural parameter of the six-degree-of-freedom parallel mechanism;
step two: presetting an initial value of a structural parameter of the six-degree-of-freedom parallel mechanism parameter calibration device, and adding a corresponding structural parameter error to the structural parameter of the six-degree-of-freedom parallel mechanism parameter calibration device;
step three: presetting nominal poses of a movable platform of a six-degree-of-freedom parallel mechanism, wherein the number of the nominal poses is greater than or equal to a lower limit value;
step four: calculating the nominal value of the expansion amount of each displacement sensor under each nominal pose;
step five: driving a six-degree-of-freedom parallel mechanism by using a controller to enable the movable platform to move to each nominal pose, and recording the actual value of the expansion amount of each displacement sensor under each nominal pose;
step six: the actual value of the expansion amount of each displacement sensor under each nominal pose is subtracted from the nominal value of the expansion amount to obtain an indication value error of each displacement sensor under each nominal pose;
step seven: constructing a mathematical model of an optimization problem by taking the minimum sum of squares of indication errors of all the displacement sensors as an objective function and taking structural parameter errors of the six-degree-of-freedom parallel mechanism and the six-degree-of-freedom parallel mechanism parameter calibration device as design variables;
step eight: searching out the optimal solution of the mathematical model by using advanced optimization software;
step nine: and substituting the optimal solution obtained by searching into a mathematical model of the six-degree-of-freedom parallel mechanism to realize parameter calibration and compensation of the six-degree-of-freedom parallel mechanism.
7. The method for calibrating parameters of a six-degree-of-freedom parallel mechanism according to claim 6,
the structural parameters of the six-degree-of-freedom parallel mechanism comprise coordinates of six hinge points on a fixed platform of the six-degree-of-freedom parallel mechanism under a fixed platform coordinate system, coordinates of six hinge points on a movable platform under a movable platform coordinate system and lengths of six branched chains.
8. The parameter calibration method for the six-degree-of-freedom parallel mechanism according to claim 6 or 7, wherein the second step comprises the following steps:
constructing a coordinate system of a measured reference block;
presetting the pose of the coordinate system of the measured reference block under the coordinate system of the moving platform of the six-degree-of-freedom parallel mechanism;
presetting the pose of the measured reference block under the fixed platform coordinate system of the six-degree-of-freedom parallel mechanism when the movable platform coordinate system is at a zero position to obtain expressions of an XOY surface, an XOZ surface and a YOZ surface of the measured reference block when the movable platform coordinate system is at the zero position;
and presetting an expression of a straight line where each displacement sensor is located.
9. The parameter calibration method for the six-degree-of-freedom parallel mechanism according to claim 6 or 7, wherein the fourth step comprises the following steps:
step four, firstly: calculating zero coordinates of each displacement sensor and a contact of a corresponding coordinate plane in the coordinate system of the reference block to be measured in the coordinate system of the fixed platform when the coordinate system of the movable platform is at the zero position;
step four and step two: calculating the position and attitude coordinates of each displacement sensor and a contact of a corresponding coordinate plane in the coordinate system of the measured reference block in the coordinate system of the fixed platform when the coordinate system of the movable platform is in the nominal position and attitude;
step four and step three: and calculating the linear distance between two contacts of each displacement sensor under each nominal pose according to the zero position coordinates and the pose coordinates to obtain the nominal value of the expansion amount of each displacement sensor under each nominal pose.
10. The method for calibrating parameters of a six-degree-of-freedom parallel mechanism according to claim 9,
when the contact of the moving platform coordinate system in the nominal pose moves towards the reference axis in the positive direction relative to the contact of the moving platform coordinate system in the zero position, the nominal value of the stretching amount of the displacement sensor is positive, and when the contact moves towards the negative direction of the reference axis, the nominal value of the stretching amount of the displacement sensor is negative.
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