Background
The off-line programming method of the spraying robot has the advantages of short programming period, capability of planning complex spraying tracks and the like, and is increasingly applied to robot spraying track planning in the fields of automobiles, ships, aerospace and the like. The spraying path planning result in the off-line programming system is a key factor for determining the spraying effect, the spraying efficiency and the paint utilization rate, and has important significance for production.
The traditional spray path planning method only pursues to meet the spray quality once, and often neglects the boundary constraint of the workpiece surface when pursuing to plan the spray path, so that the phenomenon of overspray at the workpiece boundary is serious, a large amount of paint is wasted when a spray gun sprays at the workpiece boundary, and the spray efficiency is not high. And the key point of planning the boundary constraint spraying path is to reasonably set a boundary constraint distance value according to the shape of the boundary curve of the surface of the workpiece so as to ensure that the thickness of a coating film at the boundary meets the quality requirement.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for setting a boundary constraint distance value for planning a boundary constraint spraying track, which is used for ensuring that the film thickness of the generated boundary constraint spraying track at the boundary meets the quality requirement, firstly establishing a dynamic spraying model of a spray gun along a curve path, then clarifying the influence rule of the curve shape of the boundary, the pose (spraying height and spraying inclination angle) of the spray gun on the boundary constraint distance according to the quality requirement of the film thickness, realizing the prediction of the value range of the boundary constraint distance, and finally setting the uniform value of the boundary constraint distance according to the curve shape of the surface boundary of a workpiece and taking the film thickness quality at the boundary as the requirement.
A setting method of a boundary constraint distance value of a boundary constraint spraying track planning comprises the following steps:
step 1, constructing a dynamic spraying model of a spray gun along an arc path based on an established static spraying model of the spray gun with a variable pose, wherein the space shape of a spraying torch of the spray gun is a cone;
step 2, defining a boundary constraint distance by taking the minimum allowable coating thickness at the boundary of the workpiece as a requirement, and respectively clarifying the influence rules of the curvature radius, the spraying height and the spraying inclination angle of a boundary curve on the boundary constraint distance;
and 3, setting a unified boundary constraint distance value according to the shape of the boundary curve of the surface of the workpiece to be sprayed so as to ensure that the coating thickness quality at the boundary meets the requirements everywhere.
As an improvement, in step 1, based on the established static spraying model of the spray gun with the position changed, a dynamic spraying model of the spray gun along an arc path is established, and the specific steps are as follows:
101. based on a parabolic model with a space shape of a spray torch as a cone, the parabolic model is expressed as:
assuming that the spray gun is spraying the coating material flow q
vAnd the conical opening angle phi of the spray gun is unchanged, the position and posture of the spray gun relative to the spraying surface are considered as controllable parameters, the position and posture are the spraying height H and the spraying inclination angle alpha, and after the static spraying of the position and posture change of the spray gun on the plane, a paint deposition model of any point (x, y) in the spraying amplitude range can be expressed as
Wherein A is a constant;
when the spray gun sprays at a static inclination angle, the spray width formed on the plane is in an ellipse, wherein the major axis a and the minor axis b of the ellipse are respectively as follows:
wherein, a1(H,α),a2(H, α) are respectively:
102. when the spray gun dynamically sprays along the track of the circular arc path, the radius of the circular arc path is set as r, the curvature center of the circular arc is set as O', the speed direction of the spray gun is the tangential direction of the circular arc path, the dynamic spraying speed of the spray gun on the track of the circular arc path is set as v, and the spraying speed at any point S in the spraying range is set as v
sThe radius of curvature of the arc on which the point S is located is r
SEstablishing a rectangular coordinate system by taking the curvature radius direction of the circular arc path as an x axis and the speed direction of the spray gun as a y axis, wherein
The arc length of a point S swept by the spray gun in the spray amplitude range is represented, the spraying speed of the spray gun in the tangential direction on the same arc is unchanged, and if the spray gun is fixed, the spraying process can be regarded as uniform-speed circular motion of any point S around an O' point in the elliptical spray amplitude range, so that the time of the any point S passing through the elliptical spray amplitude range is
By integrating the formula (1), a film thickness model of any point S in the spray amplitude range after the spray gun dynamically sprays along the circular arc path track is established as follows:
in the formula (6), the spraying rate at any point S and the coordinate value of the y axis where the spraying rate is located are respectively:
arc length of point S swept by the lance
Comprises the following steps:
r in formulae (7), (8) and (9)
s、
And p are each:
rS=r-x (10)
q and j in formula (12) are respectively:
by substituting formula (8) for formula (6), a model of the coating film thickness at any point S in the spray width range can be obtained.
The improvement is that in the step 2, the boundary constraint distance is defined by taking the minimum allowable coating thickness at the workpiece boundary as a requirement, and the influence rules of the curvature radius of the boundary curve, the spraying height and the spraying inclination angle on the boundary constraint distance are respectively clarified, and the method comprises the following steps:
201. assuming that the target value of the thickness of the coating film is TdObtaining a coordinate value X of the X axis on which the peak value of the thickness of the coating film is located by deriving X in the formula (6)0Specifically, the following are shown:
according to the formula (15), the spraying speed v, the spraying inclination angle alpha and the spraying height H meet a specific functional relationship, and if one parameter is known, the other two parameters can be obtained by solving the equation set;
202. the boundary constraint spraying path is generated by retracting a certain boundary constraint distance value towards the inner part of the surface of the workpiece based on a workpiece boundary curve, the boundary curve is larger than the spraying path in curvature radius by a boundary constraint distance value, and the reasonable setting of the value directly influences whether the coating thickness quality at the boundary meets the requirement or not;
the requirement of the thickness of a coating film at any point on the surface of a workpiece is set to meet TS∈[Tmin,Tmax]For this purpose, the spray path point at the boundary is defined here in the direction of the radius of curvature of the boundary curve to just meet the minimum film thickness (T)min) The distance between the boundaries is required to be boundary constraint distance, and the boundary constraint distance is divided into left and right parts according to the position relation of the boundary constraint distance relative to the spraying path, and the left and right parts are respectively d1And d2The value of which is influenced by the pose of the lance and the radius of curvature of the boundary curve, based on the numerical valueSimulating, namely clarifying the influence rule by adopting an orthogonal experiment method; according to the orthogonal experiment principle, two of H, r and alpha parameters are respectively fixed, the third parameter is used as an independent variable, the boundary constraint distance is used as a function, the influence rules of the position and the curvature radius of the spray gun and the spray path on the boundary constraint distance are respectively analyzed, and the spray path at the boundary is generated by contracting a boundary constraint distance in a boundary curve, so that the influence of the curvature radius of the spray path on the boundary constraint distance is equal to the influence of the boundary curve on the boundary constraint distance.
Has the advantages that:
compared with the prior art, the method has the following technical effects:
the invention can rapidly set a reasonable boundary constraint distance value when planning the boundary constraint spraying track in an off-line programming way so as to achieve the purpose of ensuring that the thickness of a coating film at the boundary meets the quality requirement.
Detailed Description
A setting method of a boundary constraint distance value of a boundary constraint spraying track planning comprises the following steps:
step 1, constructing a dynamic spraying model of a spray gun along an arc path based on an established static spraying model of the spray gun with a variable pose, wherein the space shape of a spraying torch of the spray gun is a cone;
step 2, defining a boundary constraint distance by taking the minimum allowable coating thickness at the boundary of the workpiece as a requirement, and respectively clarifying the influence rules of the curvature radius of the boundary curve, the spraying height and the spraying inclination angle on the boundary constraint distance;
and 3, setting a unified boundary constraint distance value according to the shape of the boundary curve of the surface of the workpiece to be sprayed so as to ensure that each point of the coating thickness quality at the boundary meets the requirement.
And (2) constructing a dynamic spraying model of the spray gun along the arc path based on the established static spraying model of the spray gun with the posture changing in the step 1, and specifically comprising the following steps:
101. based on a parabolic model with a spray torch space shape as a cone, the parabolic model is as follows:
assuming that the spray gun is spraying the coating material flow q
vAnd the conical opening angle phi of the spray gun is unchanged, the pose of the spray gun relative to the spraying surface is considered as a controllable parameter, the pose is the spraying height H and the spraying inclination angle alpha, and as shown in figure 1(a), after the static spraying of the spray gun with the changed pose on a plane, the paint deposition model of any point (x, y) in the spraying width range can be represented as follows:
where a is a constant (the value of a is different for spray guns with different flow rates, and a is a fixed value for a certain spray gun with a fixed flow rate), and the paint deposition model is shown in fig. 1 (b).
When the spray gun sprays at a static inclination angle, the spray width formed on the plane is in an ellipse, wherein the major axis a and the minor axis b of the ellipse are respectively as follows:
wherein, a1(H,α),a2(H, α) are respectively:
102. in fig. 2, let the radius of the circular arc path be r, the center of curvature of the circular arc be O', when the spray gun is dynamically spraying along the circular arc path trajectory, the speed direction of the spray gun is the tangential direction of the circular arc path, the dynamic spraying speed of the spray gun on the circular arc path trajectory is v, and the spraying speed at any point S in the spray width range is v
sThe radius of curvature of the arc on which the point S is located is r
SEstablishing a rectangular coordinate system by taking the curvature radius direction of the circular arc path as an x axis and the speed direction of the spray gun as a y axis, wherein
Indicating the arc length swept by the lance at point S over the range of the spray pattern.
When the spray gun is used for dynamically spraying along the path track of the circular arc, the spraying speed of the spray gun in the tangential direction on the same circular arc is constant, so that the spray gun is assumed to be fixed, and the spraying process can be regarded as uniform-speed circular motion of any point S around the point O' in the elliptical spraying range, so that any point S can be freely movedThe time when the intention point S passes through the elliptical spray amplitude range is
By integrating the formula (1), after the spray gun is established to dynamically spray along the circular arc path track, the film thickness model of any point S in the spray amplitude range is as follows:
in the formula (6), the spraying rate at any point S and the coordinate value of the y axis where the spraying rate is located are respectively:
arc length of point S swept by the lance
Comprises the following steps:
r in formulae (7), (8) and (9)
s、
And p are each:
rS=r-x (10)
q and j in formula (12) are respectively:
the formula (8) is substituted into the formula (6), and a specific expression of the coating thickness of any point S in the spray width range can be obtained.
The static dip spraying mentioned above means that the spray gun forms a certain dip angle with a plane and then is statically sprayed relative to the plane, and the dynamic spraying along the arc means that the spray gun moves relative to the surface.
In step 2, defining the boundary constraint distance by taking the minimum allowable coating thickness at the boundary of the workpiece as a requirement, and respectively clarifying the influence rules of the curvature radius of the boundary curve, the spraying height and the spraying inclination angle on the boundary constraint distance, wherein the method comprises the following steps:
201. assuming that the target value of the thickness of the coating film is TdObtaining a coordinate value X of the X axis on which the peak value of the thickness of the coating film is located by deriving X in the formula (6)0Specifically, the following are shown:
according to the formula (15), the spraying speed v, the spraying inclination angle alpha and the spraying height H meet a specific functional relationship, and if one parameter is known, the other two parameters can be obtained by solving the equation set;
202. the boundary constraint spraying path is generated based on a certain boundary constraint distance value of a workpiece boundary curve inwards shrinking towards the inner part of the surface of the workpiece, the boundary curve is larger than the spraying path in curvature radius by a boundary constraint distance value, and the reasonable setting of the value directly influences whether the coating thickness quality at the boundary meets the requirement or not.
The requirement of the thickness of a coating film at any point on the surface of a workpiece is set to meet TS∈[Tmin,Tmax]For this purpose, in the direction of the radius of curvature of the boundary curve, the point of the spray path at the boundary is defined so as to just meet the minimum film thickness (T)min) The distance between the boundaries is required to be boundary constraint distance, and the boundary constraint distance is divided into left and right parts according to the position relation of the boundary constraint distance relative to the spraying path, and the left and right parts are respectively made to be d1And d2The value of the curve is influenced by the pose of the spray gun and the curvature radius of the boundary curve, and the influence rule is clarified by adopting an orthogonal experiment method based on numerical simulation as shown in figure 3.
At a target coating film thickness TdTaking the cone opening angle phi of the spray gun spray torch as an example of 28 degrees, different coating film thickness distribution states can be obtained by respectively taking different parameter values of H, alpha and r to substitute in the formula (15) in the variable ranges of the position and posture parameters of the spray gun H and alpha (the variable ranges are related to the spray gun), and boundary constraint distance values under different coating film thickness distribution states are measured according to the definition of the boundary constraint distance.
According to the orthogonal experiment principle, respectively fixing H, r and two of three parameters alpha, respectively analyzing the influence rules of the pose of the spray gun and the curvature radius of the spraying path on the boundary constraint distance by taking the third parameter as an independent variable and the boundary constraint distance as a function, wherein the spraying path at the boundary is generated by contracting the boundary constraint distance in a boundary curve, and the curvature radius of the boundary curve is set as rdSatisfy rdTherefore, the influence of the curvature radius of the boundary curve on the boundary constraint distance can be obtained by analyzing the influence rule of the curvature radius of the spraying track on the boundary constraint distance.
Fig. 4, 5 and 6 show the influence rule curves of the curvature radius of the boundary curve, the spraying inclination angle and the spraying height on the boundary constraint distance respectively.
As can be seen from fig. 4, 5 and 6, under the premise that the posture of the lance is fixed, the boundary constraint distance is in a power function change relationship with the curvature radius of the boundary curve as a whole, wherein when the curvature radius of the boundary curve is greater than 400mm, the boundary constraint distance is in an almost linear change relationship with the curvature radius of the boundary curve. On the premise that the spraying height and the curvature radius of the boundary curve are fixed and unchanged, the boundary constraint distance is in a linear change relation with the spraying inclination angle. On the premise that the spraying inclination angle and the curvature radius of the boundary curve are fixed and unchanged, the boundary constraint distance is in a linear change relation with the spraying height.
According to fig. 4, 5 and 6, the rule of influence of the pose of the spray gun on the boundary constraint distance under different boundary curve curvature radii can be clarified, as shown in fig. 7, so that the minimum value and the maximum value of the boundary constraint distance at any curvature radius boundary on an irregular plane can be predicted within the variable range of the pose of the spray gun, and are respectively set as d
i minAnd d
i maxBoundary constraint distance value of
d
iWhen the value is taken in the range, the coating thickness effect meeting the spraying quality requirement can be obtained at the boundary by optimizing the position and posture of the spray gun in the range of the position and posture variable of the spray gun.
For any irregular plane, the boundary curve can be approximately regarded as the combination of a plurality of straight line segments and circular arc segments, and the analysis shows that if the boundary curve has N boundary segments with different curvature radiuses, under the premise that the posture of the spray gun is fixed, N boundary constraint distance values theoretically exist, and in order to generate a smooth and continuous spraying path at the boundary, a uniform boundary constraint distance value can be obtained at the boundary.
In order to ensure that the thickness of the coating film at any position of the boundary can meet the quality requirement, on the basis of obtaining the value range of the boundary constraint distance values of all the boundary segments, the minimum value is taken as a uniform boundary constraint distance value, as shown in the following formula:
in the direction of curvature radius of the boundary curve, the boundary curve of the patch is uniformly biased to be bound to the inside of the patchDistance d0And obtaining a boundary constraint range closed curve for generating a boundary constraint spraying path, thereby finally finishing the setting of the boundary constraint distance value.
The above description is only a preferred embodiment of the present invention, and the scope of the present invention is not limited thereto, and any simple modifications or equivalent substitutions of the technical solutions that can be obviously obtained by those skilled in the art within the technical scope of the present invention are within the scope of the present invention.