Poulos

    A mechanical arm is a mechanical device that can automatically complete the transfer or operation of objects (such as materials, workpieces, parts, or tools) according to established procedures or requirements. It can partially replace human manual labor. Higher-form manipulators can also simulate human arm movements to complete more complex tasks. Robotic arms are widely used in semiconductor manufacturing, industry, medical, military, and space exploration and other fields. So, what are the requirements for the robot arm in the design process?
1. The arm should have large bearing capacity, good rigidity, and light weight
    ​The rigidity of the arm directly affects the smoothness of the movement, the speed of the movement and the positioning accuracy when the arm grasps the workpiece. If the rigidity is poor, it will cause the bending deformation of the arm in the vertical plane and the torsional deformation of the inner side of the horizontal plane, the arm will vibrate, or the workpiece will be stuck and cannot work during the movement. For this reason, the arm generally adopts a guide rod with better rigidity to increase the rigidity of the arm, and the rigidity of each support and connecting piece must also have certain requirements to ensure that it can withstand the required driving force.
2. The movement speed of the arm should be appropriate and the inertia should be small
    The movement speed of the manipulator is generally determined according to the production cycle requirements of the product, but it is not advisable to blindly pursue a high speed.
    The arm reaches the normal movement speed from a static state to start, and from a constant speed to a stop when it stops moving, it is braking. The speed change process is a speed characteristic curve.
    The arm's weight is light, and its start and stop are smooth.
3. The arm movements should be flexible
    The structure of the arm must be compact and small to make the arm movement brisk and flexible. Installing rolling bearings or ball guide rails on the moving arm can also make the arm move lightly and smoothly. In addition, for a cantilevered manipulator, the arrangement of the parts on the arm is also considered, which is to calculate the partial gravity moment of the weight when the arm moves the part against the center of rotation, lifting, and support.
    The partial gravity moment is very unfavorable to the arm movement. If the partial gravity moment is too large, it will cause the arm to vibrate. A sinking head phenomenon will also occur during lifting, and it will also affect the flexibility of the movement. In severe cases, the arm and the column will get stuck. Therefore, when designing the arm, the center of gravity of the arm should pass through the center of rotation as much as possible, or be as close as possible to the center of rotation to reduce the deflection moment. For a manipulator that operates both arms at the same time, the arrangement of the two arms should be as symmetric as possible to the center to achieve balance.
4. High position accuracy
    In order to obtain a higher position accuracy of the manipulator, in addition to the advanced control method, the following issues should be paid attention to in the structure:
   (1) The stiffness, partial gravity moment, inertial force and cushioning effect of the manipulator all directly affect the position accuracy of the arm.
   (2) Add setting device and stroke detection mechanism.
   (3) Reasonably choose the coordinate form of the manipulator. The Cartesian coordinate manipulator has high position accuracy, its structure and movement are relatively simple, and the error is also small. The error caused by the rotary motion is the dimensional error during enlargement. When the position of the rotation angle is fixed, the longer the arm extends, the greater the error; the articulated manipulator has a complex structure, and the positioning of the hand is determined by the mutual rotation angle of each joint. The error is accumulated error, so the accuracy is poor, and its position accuracy is more difficult to guarantee.
5. Strong versatility, can adapt to a variety of operations; good manufacturability, easy to maintain and adjust
    The above requirements are sometimes contradictory. They have good rigidity and heavy load. The structure is often thick and the guide rod is large, which increases the weight of the arm. When the moment of inertia increases, the impact force is large, and the position accuracy is low. Therefore, when designing the arm, it is necessary to comprehensively consider various factors such as the grasping weight of the manipulator, the number of degrees of freedom, the working range, the movement speed, and the overall layout and working conditions of the manipulator.
    In order to achieve accurate, reliable, flexible, compact structure, high rigidity, and small dead weight, so as to ensure a certain position accuracy and adapt to rapid movements. In addition, for thermal processing manipulators, heat radiation must be considered. The arm must be longer to keep it away from the heat source, and it must be equipped with a cooling device. For dust-proof manipulators, dust-proof facilities should be installed.