Design and Analysis of Injection Manipulators

Introduction
At present, small and medium-sized injection molding enterprises in China mainly rely on manual feeding and unloading. With the rapid development of the injection molding industry at home and abroad, the traditional manual feeding and unloading can no longer meet the needs of industrialization, and it has become a trend to use robots instead of laborers.

The injection manipulator can achieve high efficiency and high-quality processing and production. According to the characteristics of loading and unloading of horizontal injection moldi ng machines, this paper designed a special manipulator for injection molding, which combined with the design requirements and site conditions, the structural design and kinematics simulation analysis of the manipulator were carried out.

1. Integral structure of injection manipulators
According to the structural characteristics and loading and unloading conditions of horizontal injection molding machines, the injection molding manipulator designed in this paper is a five-axis servo manipulator, which is mainly used for picking up workpieces or wastes. It is mainly composed of a base, a beam mechanism, a cantilever mechanism, the main arm mechanism and a hand mechanism, etc., and can move in three directions, namely the transverse movement along the beam, the up-down movement of the main arm and the pulling movement of the main arm and the auxiliary arm along the cantilever, all of which are driven by servo motors. The transverse motion is linear sliding along the guide rail driven by the servo motor. The up-and-down motion of the main arm and the auxiliary arm is up-and-down sliding driven by the servo motor, and the pulling motion of the main arm and the auxiliary arm is that the servo motor drives the slider on the main arm and the auxiliary arm to move horizontally along the cantilever, and the movement of the hand mechanism can be realized pneumatically.

2. Structural design of main components
2. 1 Structural design of the main and auxiliary arm
The main and auxiliary arm of the injection molding manipulator is the key mechanism of the manipulator. The main arm and auxiliary arm of the manipulator designed in this paper are symmetrical with each other except for the hand structure and mainly consist of a fixed arm, a movable arm and a guide rail, a timing belt, a slider and other parts. From its basic structure, it can be seen that in order to reduce the overall weight of the fixed arm and movable arm materials, aluminum alloy bars of light-weight and high-strength are used. Because of the high requirement on the rigidity, the sliding seat is made from carbon steel, and the guide rail and slider adopt the linear type and the ball type.

The structure of the main arm and the auxiliary arm is double-pitch double-speed type, and the slider connected with the cantilever guide rail is installed on the slide base. This structure is more conducive to saving space. Its working principle is that the sliding seat is fixed, and the fixed arm is mainly driven by a servo motor to move up and down. The fixed arm is equipped with a synchronous belt, and the synchronous belt fixing seat is connected with the sliding seat. The synchronous belt connecting seat is fixed on the movable arm, and the slider of the movable arm can move along the guide rail on the fixed arm. When the fixed arm moves, the synchronous belt transmits the motion to the movable arm, and the moving speed of the movable arm relative to the sliding seat is twice that of the fixed arm. The two-section telescopic structure can reduce the overall height of the injection manipulator and shorten the operation time.

2. 2 Structural design of beam parts
The crossbeam is a thin-walled hollow structure made of gray cast iron, which has high strength and lightweight, and the transverse slider is made of carbon structural steel with good rigidity. The ball linear guide rail is chosen, and the bottom of the beam is fixed on the base. The transverse slide seat is installed on the slide block of the guide rail, and the sliding seat is equipped with a servo motor, a reducer, a pulley, an idler and other parts. Driven by the servo motor, the sliding seat is led by the synchronous belt to complete the transverse movement.

2. 3 Design of the pickup assembly
The hand of the injection manipulator can be specially designed according to the specific characteristics of injection products, take and place products and recycle waste materials. Therefore, the hand structure is determined by the size, shape and weight of the product. The hand structure of the injection manipulator is generally divided into the adsorption type and the clamping type. In order to ensure the reliability of grasping, the clamping structure is generally designed with a large clamping force. Although the stability of grasping is ensured, it is easy to cause harm to products. Therefore, the clamping structure is generally used for taking and placing waste materials. The adsorption claw generally does not harm the products, and the limitation of the shape of the objects that can be grasped is small, so it is widely used to pick and place injection molded products. On the main arm of the manipulator designed in this paper, an adsorption gripper is installed to pick up and place products, and the clamping of wastes is realized by the clamping gripper installed on the auxiliary arm.

The end of the main arm mainly consists of a cylinder, a bracket, a flipper and a sensor. The whole assembly is fixed and connected with the movable arm of the main arm through the bracket. The cylinder is connected with the bracket through a shaft. The flipper is mounted on the cylinder push rod, and the flipper is connected with the bracket through a shaft. By controlling the push-pull movement of the cylinder push rod, the flipper is turned over. Two-position sensors are installed on the cylinder wall to feedback the status of the flipper.

The sub-arm end clamping mechanism mainly consists of a connecting piece, a finger cylinder and a clamp. The finger is connected with the movable arm of the auxiliary arm through a connecting piece. The finger is equipped with a clamp, which can control the clamp to realize the action of clamping and releasing when the push rod of the cylinder moves.

Conclusion
According to the characteristics of loading and unloading work of horizontal injection molding machines, a special five-axis servo manipulator for injection molding machine is designed, which is mainly used for picking up workpieces or waste materials. It is mainly composed of a base, beam mechanism, cantilever mechanism, main & auxiliary arm mechanism and hand mechanism. After simplifying the drawn three-dimensional model of injection molding manipulators, it is imported into ADAMS to analyze the kinematics of the injection molding manipulator. The curves of the displacement and velocity of the manipulator in three directions, that is, the lateral movement of the manipulator, the up-down movement of the main & auxiliary arm and the pulling movement of the main arm and the auxiliary arm along the cantilever, are obtained respectively. The curves all change smoothly without sharp angles, which proves that the manipulator can work smoothly, verifying the rationality of the design, and providing theoretical support for the motion control of the injection molding manipulator.

Jeawin Huang

Jeawin Huang

Runma Robotics Company, China professional Plastic Injection Molding Robot Automation Manufacturer, has been in robot industry for 15 years. https://www.runmarobot.com

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