Design of transmission mechanism of punch feeding and discharging manipulator

The press loading and unloading manipulator is a kind of intelligent equipment based on automation, which is specially developed for realizing the automation and unmanned production of the press shop. It can replace the worker’s work by implementing the manual editing program and greatly improve the efficiency of production and quality. The design optimized the traditional transmission scheme comparison and molded the structure based on the solid works modeling. The key supporting parts of the manipulator are analyzed by the finite element method. The simulation results showed that the manipulator can satisfy the designed loading requirements and guarantee the designed accuracy.


Introduction
In the production process of stamping, it is necessary to feed and fetch material repeatedly. Nowadays, the concept of industrial automation has been introduced into the field of production, aiming to combine mechanical production with automation and intelligence. It will turn the production process into an automated production line and reduce the human input.The robotic arm can carry out flexible movement instructions, which was accomplished by human hands.Also, it will be low cost, more reliable and efficient. [5]merica was the first country to study robots and developed a rotating, long-armed robot in the mid-20th century. The German robot was developed in the 1970s based on its solid industrial foundation and its main feature is that it is suitable for hoisting, handling, industrial welding machines, discharge machines, discharge machines and other related equipment.At the same time, the German Cooka company developed an industrial robot named FAMULUS, which is also the world's first 6-axis mechanical arm powered by electric motors.[8-9]   Due to the late development of the machinery industry in China, there is a certain gap in the research development and application of robots compared with foreign countries.Until now, industrial robots can only be seen in some large factories.Most of these robots are imported from abroad, whose high price has led to fewer applications of robots in small and medium-sized enterprises.Therefore, the development of robots has great significance for the realization of advanced manufacturing and intelligent manufacturing in our country. [10]owever, general industrial robots are expensive and are used in precision operations.So a professional industrial robot does not meet the requirements of actual production.Therefore, it is needed to design a mechanical arm that can perform simple feeding and discharging to improve the efficiency of stamping production.

The structural design
This paper mainly designed the feeding manipulator punch transmission structure, which was to simplify the structure and complete feeding and taking the material workflow.The basic requirements are as follows.(1) The manipulator can accurately clip the sheet to be processed and put it into the stamping die plate under the press.(2) The manipulator can take out and store the stamped parts or put them into the next processing area.(3) The designed manipulator should be easy to control and the design of the transmission structure should be as simple as possible while working reliably.( 4) According to the stamping environment, the transmission scheme and the size of the manipulator are reasonably selected.
In this paper, we designed the robotic arm with four degrees of freedom, which has four movement directions.It has high stability and low cost and is usually used for simple handling, assembly and disassembly.

The drive system design of the waist
When the machine is swinging, it will be subjected to a large inertial force.After clamping the plate, it should be slow to transmit torque and remove the plate from the punching machine.Therefore, the waist rotation structure adopts the worm-gear transmission scheme and the advantage of this design is to sacrifice the high speed of the motor in exchange for greater torque and slower and more stable rotation.It is shown in Figure 1.

The drive system design of the lifting mechanism
The lifting part of the manipulator is arranged on the upper part of the waist rotation.The lifting mechanism is driven by an AC servo motor and the output shaft transmits torque through the elastic coupling connecting the screw shaft.The waist screw of the robot is connected to the upper arm of the manipulator by the sliding table.The four sliding rails move up and down to guide the manipulator's movement while also playing a supporting role to ensure the strength requirements.When the lead screw rotates, the sliding table will drive the robot to achieve up-and-down movement.The schematic of the manipulator lifting mechanism is shown in Figure 3.

The drive system design of the manipulator's arm
The mechanical arm is usually composed of a power device, connecting components and other components.The manipulator end is connected to the wrist, which can realize the overall movement of the manipulator in space and free telescopic rotation.When the manipulator is moving, additional dynamic load and adverse collision should be avoided as much as possible.The reasonable assembly should be carried out on the premise of maintaining the moving speed of the manipulator.
The servo motor is connected to the lead screw through the synchronous belt.When the transmission ratio is one, it can smoothly output the motor torque to the lead screw.The telescopic part of the manipulator is driven by a screw, which has a simple structure, high transmission efficiency, stable operation and fast response speed.It is very suitable for the action of loading and unloading plates in the punch press.The material of the mechanical arm is made of aluminum alloy with lightweight and certain strength and stiffness.It can be ensured that the load on the end joint is reduced as much as possible when the manipulator is clamping the workpiece.The schematic of the manipulator arm is shown in Figure 5. Figure 6.The modeling of the arm.It is similar to the waist lifting mechanism, except that the stroke changes from up and down to the relative telescopic movement of the big arm and the forearm.The modeling of the manipulator arm mechanism is shown in Figure 6.

The drive system design of manipulator's forearm
The design of the wrist only needs a servo motor to control the clamping direction of its claw.If the suction cup is directly connected, it will increase the control difficulty and make it difficult to grasp the rotation accuracy, because of the motor's high speed.So the servo motor should be connected to a reducer deceleration and then the reducer is connected to the claw body.
The clamp at the end of the manipulator adopts the design of four suction cups (as shown in Figure 7).The extension rod is set to reduce the weight and increase the distance of the suction cups so that it can absorb the plate more smoothly and reduce the clamping accuracy requirements.The reason for the use of a suction clamp claw is that the stamping material is mostly sheet-like.The use of a mechanical clamp claw is not good for clamping and requires a larger size.The use of suction can avoid this problem.The flexible suction will not damage the plate.If the manipulator action is too large, it can rely on the cushioning effect of the suction cup to avoid damage to parts.Figure 8.The modeling of the forearm.The suction cup is connected to the vacuum pump and the air inside the suction cup is drawn out through the vacuum pump to generate negative pressure inside the suction cup to adsorb and clamp the workpiece.After reaching the stroke, the vacuum pump stops inhaling and releases the air.When the internal and external atmospheric pressure of the suction cup is the same, the suction force is lost and the sheet material is released.If the design is not reasonable, the suction cup will not correctly fit the sheet material, resulting in a vacuum environment to suck up the sheet material.The end picker is composed of a suction cup, and the rotation of the suction cup is controlled by the motor and the reducer mechanism.The modeling of the manipulator arm mechanism is shown in Figure 8.
The overall structure can be determined by the above design content, which is shown in Figure 9.The modeling of the manipulator arm mechanism is shown in Figure 10. Figure 10.The modeling of the overall structure.

The stress analysis of the mechanical hand
According to the movement requirements of the manipulator, the big arm part bears the greatest load.So the mechanical analysis of the horizontal plate at the support of the big arm is carried out and the material is set as the 6061 aluminum alloy.
According to the actual structure of the manipulator, the support point, the force position and the force size are selected.The force situation is analyzed by using the software after the grid.Given that the overall weight of the mechanical arm is 45 kg and the load is 5 kg, the mechanical arm is fully loaded.So the force part of the mechanical arm is set at the end size of 500 N for mechanical simulation.
The allowable stress of the aluminum alloy material is 1.408×10 8 N/m 2 .When the maximum load is 500 N, the maximum stress of the end is 5.515×10 7 N/m 2 , which is within the allowable range.According to the precision requirements of the manipulator to the punching press, the deformation of the material is within the accuracy range.Therefore, the structure is feasible, as shown in Figure 11.

Conclusions
The manipulator designed in this paper can reduce the labor intensity of loading and unloading and achieve the purpose of automatic loading and unloading.The design of the automatic loading and unloading manipulator in stamping production fully considers the high degree of freedom required by the mechanical arm and the good adaptability to various production environments.At the same time, because its structural design follows the principle of simplifying as much as possible, it is very easy to add components on this basis so that it can adapt to various production environments.Therefore, the application of robots in the factory performing handling, loading and unloading and other operating environments will have great potential.

Figure 1 .
Figure 1.The schematic of the manipulator waist.

Figure 2 .
Figure 2. The modeling of the manipulator's waist.The rotating part of the waist is driven by the servo motor to drive the worm.The worm drives the turbine to rotate and the whole upper of the robot is fixed by the flange plate through the turbine shaft.The modeling of the manipulator's waist is shown in Figure 2.

Figure 3 .
Figure 3.The schematic of the lifting mechanism.

Figure 4 .
Figure 4.The modeling of the lifting mechanism.The waist seat of the manipulator is composed of a servo motor, ball screw, elastic coupling, linear slide rail, bearing, slide base plate and screw fixing seat.The motor drives the ball screw to rotate and the manipulator moves up and down along four guide rails.The modeling of the manipulator lifting mechanism is shown in Figure 4.

Figure 5 .
Figure 5.The schematic of the arm.Figure6.The modeling of the arm.It is similar to the waist lifting mechanism, except that the stroke changes from up and down to the relative telescopic movement of the big arm and the forearm.The modeling of the manipulator arm mechanism is shown in Figure6.

Figure 7 .
Figure 7.The schematic of the forearm.Figure8.The modeling of the forearm.The suction cup is connected to the vacuum pump and the air inside the suction cup is drawn out through the vacuum pump to generate negative pressure inside the suction cup to adsorb and clamp the workpiece.After reaching the stroke, the vacuum pump stops inhaling and releases the air.When the internal and external atmospheric pressure of the suction cup is the same, the suction force is lost and the sheet material is released.If the design is not reasonable, the suction cup will not correctly fit the sheet material, resulting in a vacuum environment to suck up the sheet material.The end picker is composed of a suction cup, and the rotation of the suction cup is controlled by the motor and the reducer mechanism.The modeling of the manipulator arm mechanism is shown in Figure8.The overall structure can be determined by the above design content, which is shown in Figure9.The modeling of the manipulator arm mechanism is shown in Figure10.

Figure 9 .
Figure 9.The schematic of the overall structure.Figure 10.The modeling of the overall structure.

Figure 11 .
Figure 11.The figure of material stress analysis.The allowable stress of the lead screw material is 1.15×10 9 N/m 2 .According to the maximum torque of the servo motor of the mechanical arm, the force of the lead screw is set to 0.3 N•m. the maximum stress of the end is 5.15×10 8 N/m 2 , which is within the allowable range.Therefore, the structure is feasible, as shown in Figure12.

Figure 12 .
Figure 12.The figure of material stress analysis.