The hottest robot arc spraying flexible rapid prot

Preliminary exploration of robot arc spraying flexible rapid prototyping technology based on remanufacture

Introduction

equipment remanufacture engineering is an effective way to save resources, protect the environment, upgrade and transform old equipment and accumulate experience for new equipment. It is not only the inheritance, development and deepening of maintenance engineering and surface engineering, but also its theorization and systematization. It is to create a conservation oriented society, build a circular economy An important technical way to adhere to the strategy of sustainable development

due to the unprecedented cruelty of modern war, equipment damage is becoming increasingly serious, and precision assurance is imminent. At the same time, due to the complexity of modern weapons and equipment, high quality, multiple varieties, small batch, short cycle requirements, and difficult repair, these ceramic phases always exist in a three-dimensional situation. The traditional batch production technology is remanufacturing the quality, efficiency, accuracy, and labor intensity of products, Reducing environmental pollution and other aspects can no longer meet the needs of modern war. Therefore, the development of automated, flexible and intelligent rapid manufacturing technology has become an important topic in front of the military of all countries by 2022. Adopting the rapid production technology of automation, flexibility and intelligence can also reduce the inventory backlog, reduce the support expenditure and improve the support level. It also has important strategic and military significance for the rapid repair and accurate support of parts in long-distance navigation, land, air, space and other harsh environments such as high temperature and severe toxicity. At the same time, in the modern economic society, the market competition is fierce, and the adoption of this technology can greatly improve the flexibility of enterprises to manufacture small batch and multi variety products, enhance the competitiveness of enterprises and market resilience. Therefore, the development of automation, flexibility and intelligent rapid production technology has broad research, development and application prospects in national defense and national economy corrosion resistance (doing experiments in solution), Robot arc spraying flexible rapid prototyping technology based on remanufacturing is one of its contents

robot arc spraying flexible rapid prototyping technology based on Remanufacturing refers to the technology of rapidly manufacturing equipment parts (mainly thin-walled parts) of arbitrary shape by arc spraying under the control of robot operation and directly driven by CAD model. It is the product of multi-disciplinary infiltration and intersection of mechanical engineering, CAD, automatic control, arc spraying and material energy. It is a technology that automatically, quickly and accurately turns design ideas into prototypes with certain functions or directly manufactures parts

this paper preliminarily discusses the composition, characteristics, working process and path planning method of robot arc spraying flexible rapid prototyping technology, and prospects the future development of this technology

1 system composition

robot arc spraying flexible system is mainly composed of robot body and controller, arc spraying equipment, positioner, peripheral devices and control system

industrial robots used for spray molding basically belong to six axis joint robots, and the payload is generally 6kg or 16KG. The movement of the lower three axes (arms) is to send the spray gun to different spatial positions, and the upper three axes (wrists) is to solve the posture problem of the spray gun. The movement of each joint is driven by AC servo motor, which has good dynamic characteristics, strong load capacity and low failure rate, The acceleration (deceleration) of each axis is also very fast. The robot controller is the center of the whole system. It is composed of computer hardware, software and some special circuits. The software includes controller system software, robot language, robot kinematics and dynamics software, robot control software, robot simulation software, robot self diagnosis and sub protection software, The controller is responsible for all information in the working process of the robot and all actions of the robot

arc spraying equipment generally consists of spray gun, spraying power supply, wire feeding mechanism and auxiliary mechanism. In order to ensure that the robot controller can control and program the spraying parameters, the interface protocol between the robot and the spraying equipment must be consistent

the positioner is mainly used to coordinate the movement with the robot in the spraying process and be in a proper position in order to obtain parts with good molding quality

peripheral devices mainly include workpiece fixtures and safety anti-collision devices

the control system adopts i/o high-speed bus control with a series of programmable controllers as the core, which is mainly composed of control box, teaching pendant, etc. the teaching pendant is equipped with a programmable terminal (touch screen), which can complete all operations, provide various instructions and parameter input, especially when adjusting fixtures or operating procedures, it can be easily realized through the programmable touch terminal without replacing hardware

2 technical features

(1) high speed, high flexibility and high technology density realize the integration of design and manufacturing

(2) free form manufacturing, which is not limited by the complexity of parts, and realizes the flexible production of sprayed parts

(3) without traditional tools, fixtures and molds, the stability of spraying parameters is maintained, and the consistency of part forming is improved

(4) short production cycle, fast market response, high production efficiency and strong product competitiveness

(5) the production cost is low, the quality of parts is high, and the cost is only 1/3 1/5 of that of traditional processing. It has outstanding economic benefits, material saving, energy saving, environmental protection, and conforms to the concept of green production

(6) it can realize the zero inventory of spare parts of weapons and equipment and the rapid and accurate guarantee of the battlefield, which is of great military significance

3 working process

robot arc spraying flexible rapid prototyping manufacturing technology is different from traditional forced forming (such as forging forming) and removal forming (such as machining), which is a forming process based on discrete accumulation. First, with the help of 3D CAD or reverse engineering, the combined information of geometry, structure and materials of parts is obtained, so as to obtain the concept of target prototype, and then establish a digital description model. After that, these information is output to the computer-controlled electromechanical integrated manufacturing system, and the material is "three-dimensional stacked" shaped point by point and side by side, and then necessary processing is carried out to make it meet the design requirements in terms of appearance, strength and performance. Its general working process is: 1) establish a three-dimensional CAD data model; 2) Discretization processing; 3) Level information processing; 4) Determine the powder material, adopt the arc spraying process, and process the layer; 5) Spray and stack manufacturing of prototypes or parts; 6) Post processing of prototype or parts

4 path planning method

robot trajectory planning is to make the robot move from the initial state to a specified target state at a certain speed and acceleration within a specified time. Its comprehensive quality upgrading project path planning methods mainly include rectangular coordinate space method and joint space method. The advantages of joint space method are small amount of calculation, high efficiency, limited only by joint speed and acceleration, and there will be no singularity of the mechanism. It is especially suitable for the trajectory segment where the robot end effector leaves the object without requiring a specified path and enters a large range of empty travel to move quickly. The disadvantage of this method is that it is difficult to visualize the real trajectory of the end effector in space before the robot executes the end execution instructions to realize movement, Especially when there are obstacles in the robot workspace, it is prone to danger. The advantage of rectangular coordinate space trajectory planning is that the motion between segment points can be well determined, which is very suitable for the defined function trajectory. The disadvantage is that it not only needs to carry out spatial interpolation, but also needs to convert to joints, and it is difficult to estimate the limit of motion time, joint speed and acceleration

4.1 rectangular coordinate space method

in the arc spraying rapid prototyping process, it requires not only the robot to accurately locate the end point of motion, but also the motion trajectory to have a certain accuracy, that is, it requires the continuous path control of the arm. In order to ensure reliable grasping and unloading of the spray gun, a preparatory action is required, so two positions of approaching and disengaging need to be added. At the same time, in order to avoid unnecessary jitter and pause, the actuator is often required to move continuously when passing through these space points

cp include spatial linear motion, spatial circular motion and spatial elliptical motion

(1) space linear motion

at this time, the robot only needs to complete a space linear trajectory in motion, and its trajectory control adopts the linear interpolation method in rectangular coordinate space. As long as the pose information of the starting point and the ending point of the trajectory in the rectangular coordinate space is given, the pose information of a series of points on the straight line segment determined by two points can be calculated. Through the inverse kinematics solution of the position and posture of this series of points, the required joint angle of the corresponding points of each joint can be obtained

(2) spatial circular motion

in addition to simple lines, arcs, ellipses, three-dimensional spatial trajectories also include complex curves such as parabola, hyperbola, helix, etc. Let the robot pass through a point T16 in the middle from the starting point pose T06 to the ending point T26. In the X, y, z directions of the fixed coordinate system, the starting point position is p*0= (p*0x, p*0y, p*0z) t, and the attitude angle is α 0 β 0 γ 0 the position of the middle point is p*1= (p*1x, p*1y, p*1z) t, and the attitude angle is α 1、 β 1、 γ 1. The position of the end point is p*2= (p*2x, p*2y, p*2z) t, and the attitude angle is α 2、 β 2、 γ 2。

if the above formula is used for trajectory planning according to the spatial circle equation: (x-x0) *2+ (y-y0) *2+ (z-z0) *2=r*2

, it is very difficult to write the parameter equation of the trajectory, and the interpolation of the above equation is also very complex. In order to calculate the trajectory equation of the circle conveniently, the trajectory equation of the circle must be transformed from the fixed coordinate system first, and then the trajectory planning interpolation is introduced into the new coordinate system, and then it is inversely transformed into the reference coordinate system

(3) spatial elliptical motion

the elliptical motion mode of welding robot is similar to the circular motion mode, but the difference is that it is planned with ellipse. According to any three points on the trajectory, and given the ratio of long and short axis k=a/b, the trajectory planning of the ellipse can be carried out. When a=b, the trajectory planning of ellipse is the trajectory planning of circle

4.2 joint space method

first convert the path points into joint vector angle values with inverse kinematics, then fit a smooth function for each joint, pass through all path points in turn from the initial point to the target point, and make the motion time of each joint in each path the same. The joint trajectory should meet a set of constraints at the same time, such as posture, velocity, acceleration and continuity. Under the constraint conditions, different types of joint interpolation functions can be selected. Commonly used interpolation functions include cubic polynomial interpolation, high-order polynomial interpolation and linear interpolation with parabolic transition. The joint functions are independent of each other, and the singularity of the mechanism will not occur

(1) PTP motion without intermediate point

PTP motion without intermediate point refers to the motion of the robot's hand without passing through any intermediate position and attitude point when it moves from a certain position and attitude at the starting point of the robot to another position and attitude at the end point. Let the initial pose of the robot be t*06, and then several joint angles of the pose are q*0i (i=1, 2,..., 6). After time TF, the robot hand directly reaches the target pose t*16 without any other intermediate point, and the corresponding joint position is q*1i (i=1, 2,..., 6). In order to make the robot's motion coordinate quickly, the smooth function Qi (T) must be found. Cubic polynomial interpolation: Qi (T) =a0+a1t+a2t*2+a3t*3 joint motion starts from the stationary starting point and ends at the stationary end. The four coefficients can be obtained from the constraints of the starting point and the ending point

(2) PTP movement with intermediate point