For industrial robots, material handling is one of the most important applications of their gripping operations. As a highly versatile piece of equipment, the successful completion of tasks by industrial robots depends directly on their gripping mechanism. Therefore, the gripping mechanism at the robot's end effector must be designed in accordance with the actual task and the requirements of the working environment, which leads to a diversity of gripping mechanism structures.
Figure 1. Relationship between end effector elements, characteristics, and parameters
Most mechanical clamping mechanisms are two-finger claw types, which can be divided into rotary and translational types according to the movement of the fingers; they can also be divided into internal support and external clamping types according to the different clamping methods; and they can be divided into pneumatic, electric, hydraulic and their combination clamping mechanisms according to structural characteristics.
I. Pneumatic end-effector clamping mechanism
Pneumatic systems offer convenient air supply, fast response times, and a pollution-free working medium. They also boast superior fluidity compared to hydraulic systems, exhibiting lower pressure loss and suitability for remote control. The following are some examples of pneumatic robotic arm devices:
1 -turn linkage lever clamping mechanism
The fingers of this device (such as V -shaped fingers or arc-shaped fingers) are fixed to the clamping mechanism by bolts, making replacement relatively convenient and thus significantly expanding the application range of the clamping mechanism.
Figure 2. Structure of the rotary linkage lever clamping mechanism
2. Straight rod type double cylinder translation clamping mechanism
The fingers of this clamping mechanism are usually mounted on a straight rod equipped with a finger mounting seat. When pressurized gas enters the two rod chambers of a single-acting double cylinder, it pushes the piston to gradually move towards the middle until the workpiece is clamped.
Figure 3. Structural diagram of the straight rod type double cylinder translation clamping mechanism
3 -link cross-type double cylinder translation clamping mechanism
It typically consists of a single-acting double cylinder and interlocking fingers. When air enters the central chamber of the cylinder, it pushes the two pistons to move to both sides, thereby driving the connecting rod to move, and the interlocking fingers will firmly fix the workpiece; if no air enters the central chamber, the pistons will return to their original position under the action of the spring, and the fixed workpiece will be released.
Figure 4. Structural diagram of the cross-type double-cylinder translation clamping mechanism
4. Internal support linkage lever clamping mechanism
Force is transmitted through a four-bar linkage, with its clamping direction opposite to that of an external clamp, primarily used for gripping thin-walled workpieces with internal holes. After the clamping mechanism clamps the workpiece, three fingers are typically installed to ensure it can be smoothly positioned using the internal hole.
Figure 5. Structural diagram of the internal support linkage lever clamping mechanism.
5. Fixed rodless piston cylinder driven force amplification mechanism
The pneumatic system of the fixed rodless piston cylinder is shown below. This cylinder is a single-acting cylinder, which is reversed by spring force and is switched by a two-position three-way solenoid valve.
Figure 6. Pneumatic system of a fixed rodless piston cylinder
A transition slider is installed radially on the piston of the rodless piston cylinder, and two hinge rods are symmetrically hinged at both ends of the slider. If an external force is applied to the piston, the piston will move left and right, thereby pushing the slider up and down. When the system is clamped, hinge point B will make a circular motion around point A , and the up and down movement of the slider can increase a degree of freedom, replacing the oscillation of the entire cylinder body with the oscillation of point C.
Figure 7. Force-boosting mechanism driven by a fixed rodless piston cylinder.
Internal clamping pneumatic device of 6- hinged rod and 2- lever tandem force amplification mechanism
When the directional control valve for compressed air is in the left-hand position as shown in the diagram , compressed air enters the left chamber (rodless chamber) of the pneumatic cylinder. The piston moves to the right under the air pressure , gradually decreasing the hinge pressure angle α . This angle effect amplifies the air pressure, which is then transmitted to the lever of the constant-force lever mechanism. The force is amplified again, becoming the force F that clamps the workpiece . When the directional control valve is in the right-hand position, compressed air enters the right chamber (rod chamber) of the pneumatic cylinder , pushing the piston to the left , and the clamping mechanism releases the workpiece.
Figure 8 shows the internal clamping pneumatic manipulator of the hinge 2 lever series force amplification mechanism.
II. Pneumatic end-effector clamping mechanism
A pneumatic suction end-grip mechanism uses the suction force created by the negative pressure within a suction cup to move objects. It is mainly used for gripping relatively large, moderately thick, and low-rigidity objects such as glass, paper, and steel. Based on the method of generating negative pressure, it can be divided into the following types:
1. Squeeze suction cup
The air inside the suction cup is forced out by downward pressure, creating negative pressure inside the suction cup and forming suction to hold the object. It is used to grip workpieces that are small in shape, thin in thickness, and light in weight.
Figure 9. Structure diagram of the extrusion suction cup
2. Airflow negative pressure suction cup
The control valve injects compressed air from the air pump into the nozzle. The flow of compressed air generates a high-speed jet, which carries away the air in the suction cup, thus creating a negative pressure in the suction cup. The suction force formed by the negative pressure can then hold the workpiece.
Figure 10. Structure diagram of airflow negative pressure suction cup
3 Vacuum pump exhaust suction cup
An electromagnetic control valve connects a vacuum pump to a suction cup. When air is pumped out, the air inside the suction cup cavity is drawn away, creating a negative pressure that attracts the object. Conversely, when the control valve connects the suction cup to the atmosphere, the suction cup loses its suction force and releases the workpiece.
Figure 11. Structure diagram of vacuum pump exhaust type suction cup
Hydraulic end clamping mechanism
1 Normally closed clamping mechanism
The drill string is secured by the strong preload of springs and then hydraulically released. When the clamping mechanism is not performing a gripping task, it is in the state of clamping the drill string. Its basic structure consists of a set of pre-compressed springs acting on a force-increasing mechanism such as an inclined plane or lever, causing the slip seat to move axially, which in turn drives the slips to move radially, clamping the drill string; high-pressure oil enters the hydraulic cylinder formed by the slip seat and the outer shell, further compressing the springs, causing the slip seat and slips to move in opposite directions, releasing the drill string.
2 Normally open clamping mechanism
Typically, a spring-loaded release and hydraulic clamping method is used, with the clamping mechanism in a released state when not performing a gripping task. The clamping force is generated by the thrust of the hydraulic cylinder. A decrease in oil pressure will lead to a decrease in clamping force, so a reliable hydraulic lock is usually installed in the oil circuit to maintain oil pressure.
3. Hydraulic tensioning clamping mechanism
Both loosening and clamping are achieved hydraulically. If high-pressure oil is supplied to the oil inlets of both hydraulic cylinders, the slips will move towards the center with the piston movement to clamp the drill bit. If the high-pressure oil inlet is changed, the slips will move away from the center and loosen the drill bit.
4. Composite hydraulic clamping mechanism
This device has a main hydraulic cylinder and an auxiliary hydraulic cylinder. A set of disc springs is connected to the side of the auxiliary hydraulic cylinder. When high-pressure oil enters the main hydraulic cylinder, it pushes the cylinder body of the main hydraulic cylinder to move. The force is transmitted to the slip seat on the side of the auxiliary hydraulic cylinder through the push column. The disc spring is further compressed, and the slip seat moves. At the same time, the slip seat on the side of the main hydraulic cylinder moves under the action of the spring force, releasing the drill bit.
IV. Magnetic end-effector clamping mechanism
There are two types of chucks: electromagnetic chucks and permanent magnet chucks. Electromagnetic chucks use the switching of current in a coil to generate and eliminate magnetic force to attract and release ferromagnetic objects. Permanent magnet chucks, on the other hand, use the magnetic force of a permanent magnet to attract ferromagnetic objects. They achieve this by moving a magnetically shielded object to change the magnetic field loop within the chuck, thus attracting and releasing the object. However, although both are chucks, permanent magnet chucks have a weaker attraction than electromagnetic chucks.
Special Note: Some materials in this article are from the internet, and the copyright belongs to the original author.
