Design of the hottest multi-step handling manipula

2022-08-12
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With the popularization and development of industrial automation, the demand for controllers is increasing year by year. The shell is a general-purpose part used in valve controllers, which has complex structure, high machining accuracy and long process. The quality of the shell has always been one of the main indicators affecting the accuracy of the controller. Due to the old processing equipment and backward technology of the original shell, the development of the controller is seriously affected. In order to change the backward production state and alleviate the increasingly tense relationship between supply and demand, we have developed a multi-step handling manipulator. In terms of the overall conception, overall layout, mechanism function, drive and control system of the equipment, the original equipment has been completely transformed. Since it was put into operation, the product quality has been stable, the productivity has been high, and the process cost has been reduced, which is deeply welcomed by the manufacturers

2 process and overall layout

the shell is made of non-ferrous metal alloy with the brand of HPb59-1, which is formed by metal die casting, and the blank precision is high. In order to meet the design requirements, generally, the outer surface of the shell is used as the process benchmark to process the shell end face and positioning stop, and then the stop, end face and shell boss are used as the positioning benchmark to process five radial stepped holes distributed radially on the circumference of the shell. The processing of radial hole system needs to be completed by 12 steps, among which the processing process of hole 1 and hole 2 is: drilling - tapping - drilling small holes. The processing process of hole 3, hole 4 and hole 5 is drilling tapping. Multi step handling manipulator is a special equipment for processing radial holes of shell. The whole machine is composed of seven parts: frame, power head, manipulator, fixture, chip removal mechanism, hydraulic drive and control system. The whole process and overall layout are shown in Figure 1

Fig. 1 process and overall layout

the whole machine is in an I-shaped frame structure. 13 manipulators are hoisted on the guide rail above the frame, and 13 auxiliary positioning fixtures are set on the working table below. Among them, the transposition action of 4 fixtures No. 3, 6, 8 and 10 is completed by the transmission pair composed of transposition hydraulic cylinder, tooth bars and gears. Except for No. 0 fixture, 12 power heads in linear arrangement are installed behind the other 12 fixtures for drilling and tapping. The feed and retreat of the power heads are controlled by 12 cams installed on the distribution shaft respectively. The power of the distribution shaft is provided by the main motor (1.5 kW, 1440 R/min) through the planetary cycloid reducer to drive the worm gear and worm mechanism. The initial position of each power head can be completed by their respective adjustment mechanisms. In order to facilitate chip removal, a chip removal motor controlled by a counter is set under the power head and fixture. After deceleration, the conveyor belt is started for chip removal, and the chips can be automatically cleaned every 5 workpieces without stopping the machine

3 design of multi-step handling manipulator

3.1 structure composition and working principle

the multi-step handling manipulator we designed is a two degree of freedom manipulator with rectangular coordinates. Its functional symbols and structure are shown in Figure 2

1. Connecting screw 2 Lifting hydraulic cylinder 3 Bend, guide screw 4 Clamping hydraulic cylinder

5 Grab 6 Hinge 7 Workpiece 8 Positioning element 9 Shim 10 Spherical washer

11 Connecting rod 12 Small piston rod (force transmission mechanism) 13 Transverse cylinder

Figure 2 functional symbols and structural schematic diagram

a single rod double acting hydraulic cylinder is installed on the guide rail of the whole machine frame, and the cylinder block is fixed. 13 manipulators are rigidly hoisted on the slider connected with the piston rod. Due to the resonance principle, when the piston rod moves, the 13 manipulators can synchronously complete the left and right horizontal movement. The arm of the manipulator is a telescopic composite hydraulic cylinder, the piston rod of the arm cylinder is the cylinder block of the clamping cylinder, and the piston rod of the clamping cylinder acts as a force transmission mechanism to drive the internal caliper 4-finger gripper with the pin shaft as the hinge to complete the grasping and release of the workpiece. In order to prevent the torsion caused by uneven force from affecting the positioning accuracy of the workpiece during the rising and falling movement of the arm, a guide screw is installed on the arm piston rod, and the screw cooperates with the bending chute on the end cover for axial guidance. The lip end face and outer diameter of the lower cover of the clamping cylinder are used as the first and second benchmarks for workpiece processing respectively. 13 manipulators complete the self positioning and clamping of the workpiece at the same time, and carry the workpiece together for inter process conversion, which greatly improves the productivity

3.2 accuracy design of manipulator

the accuracy design of manipulator requires accurate positioning of workpiece, high grasping accuracy, good repeated positioning accuracy and motion stability, and sufficient grasping ability

according to the design requirements of the shell parts, the parallelism, perpendicularity and coaxiality of the stepped radial hole system with the shell end face and the center line of the positioning seam have strict accuracy requirements (0.1 mm). In the design, we take the rotation center line of the power head and the center line of the fixture to automatically calculate the coaxiality between the experimental results to be 0.06 mm, and the perpendicularity between the rotation center line of the power head and the center line of the manipulator to be 0.03 mm. At the same time, we also put forward higher requirements for the positioning accuracy of the manipulator

follow the principle of datum coincidence. During machining, take the end face and outer diameter of the lip on the lower cover of the clamping cylinder as the first and second datum planes to remove three degrees of freedom and two degrees of freedom of the workpiece respectively, and remove the sixth degree of freedom from the fixture by the boss of the end face outside the shell. In the design, the positioning element of the fixture is selected as a cone structure to ensure that the workpiece has a high degree of neutrality and that the workpiece can be well self positioned when clamped (the outside of the workpiece is similar to a sphere). The accuracy of the circumferential position of the radial step hole of the workpiece is guaranteed by the indexing fixture

the workpiece is installed in the fixture of the worktable under the frame, and the manipulator is hoisted on the slide rail above the frame. Each workpiece needs 12 times of handling by the manipulator to complete the whole process, so the grasping accuracy of the manipulator is very important in the design. There are many factors that affect the grasping accuracy of the manipulator, such as: the parallelism T1 of the guide rail on the frame facing the worktable at the lower part of the frame, the perpendicularity T2 of the center line of the positioning element in the fixture to the worktable, the perpendicularity T3 of the center line of the manipulator to the mounting surface of the guide rail, and the center 2 of the manipulator The coaxiality of the zigzag experimental line and the center line of the fixture positioning element (omitting the coaxiality error between the workpiece center line and the center line of the positioning element), that is, the gripping accuracy of the gripper is the closed ring t Σ, forming the dimension chain as shown in Figure 3

Figure 3 dimension chain

in the design, we take the gripping accuracy t Σ =0.1 mm, then the tolerance allocated to each constituent ring is: t1=0.05/220, t2=0.03/130, t3=0.03/400, at the same time, take the perpendicularity of the locating end face of the stop at the lower end of the clamping cylinder and the outside diameter of the stop as 0.03mm, and take the matching size of the locating outside diameter of the stop and the inside diameter of the workpiece stop as ∅ 44a11/G8, that is, the size of the hole is 44a11 (+0.48+0.32), The outer diameter, which is equivalent to the size of the shaft, is 44g8 (-0..048), so the maximum fit clearance can be calculated as 0.528mm, and the minimum fit clearance is 0.329mm, which can meet the requirements of grasping accuracy. The beneficial conditions for the export of China's plastic extruder with matching accuracy in the compound hydraulic cylinder of the manipulator are increasing, and the design is determined with reference to the design requirements of the hydraulic cylinder

since 12 manipulators are fixed and hoisted on the sliding block of the piston rod of the traverse cylinder, the design accuracy between the manipulators is taken as ± 0.03 mm. The traverse cylinder uses sensors and mechanical stops as the positioning system, and the movement speed of the manipulator is not high(

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