Gripping Systems for Increased Versatility

Comparatively simple grippers are used in an increasing number of applications where various part sizes have to be handled quickly and processed reliably. SCHUNK explains.

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Those in the automotive industry who want to stay flexible in manufacturing need space for gripper storage stations and changing systems. Gripper changes often cause unproductive auxiliary process times, which reduce efficiency. Therefore the trends in the one-piece series production are heading toward universal plants and flexible automated solutions with multifunctional, servo-electric driven gripping systems. They are very flexible and grip various parts in alternating succession.

Because of the increasing variety in models, motors and equipment can only be produced profitably if the automated solutions can be flexibly adjusted in a short time. While robots allow a high degree of flexibility during the sequences of movements, the alternating gripping of various components remains a challenge. Comparatively simple grippers are used in an increasing number of applications where various part sizes have to be handled quickly and processed reliably. In the automotive industry, where space and time are extremely critical factors, the trends go to multifunctional, servo-electrically driven gripping systems.

Motor and Gear Manufacturing Play Pioneering Role
For motor and gear manufacturing, efficient solutions already exist that allow flexible handling of various crankshafts, cylinder heads, or motor blocks. Special grippers equipped with a compensation unit, for example, can handle four different cylinder head types with a weight of up to 95 kg. For this purpose the compensation unit rests on a floating bearing and is then locked eccentrically. A stroke of 342 mm allows gripping components of different sizes. Due to the compact axes that carry the wheel rims, the gripper has optimized size/contours for confined spaces. The gripper is integrated into the existing robot control unit and does not require any additional control unit or regulator.

Simultaneous Engineering Required
Flexible automated solutions for automotive welding and assembly lines are far more complex. For achieving process-reliable handling, numerous factors have to be considered, such as the large variety of part sizes, varying surfaces, and different positions of possible gripping points, as well as the handling of occurring forces and vibrations. It would be ideal if the parts and plant design could be done at the same time. During the design process of car parts, for example, identical clamping and gripping points can be defined, considerably increasing the plant’s later degree of efficiency. Figure 1

Flexible Lightweight Grippers
In addition to flexibility, the lightweight gripper now plays an increasing role for the design work of gripping systems. Integrated into the system, the lightweight grippers save energy at the same efficiency, or achieve at the same energy consumption a considerably higher efficiency. In both cases efficiency of the complete system increases, which is why lightweight grippers are perfect for manufacturers, system integrators, and users.

A development example resulting from a cooperation between the manufacturer FFT EDAG, the robot manufacturer FANUC Robotics, and SCHUNK provide ideas on how flexible a clamping and gripping system for the vehicle manufacturing could look like. The SCHUNK LEG long-stroke electric gripper is used as a positioning unit of side skirts. The standardized lightweight gripper in the modular design weighs 8.8 kg, disposes of an enormous gripping force of 1140 N, and a variable stroke between 0 mm and 568 mm. For the use in this plant it was equipped with a servo-electric drive from the robot manufacturer. By means of a plug-and-play connectivity, the gripper works like an additional robot axis and can be actuated with the same instruction set. The flexible assembly group is combined with a six-axis robot and an additional robot used as a flexible clamping device. Two degrees of freedom at the gripper, five at the device, and six at the robot open up a new spectrum of possibilities. Figure 2

Composites are Popular
New and considerably more efficient manufacturing methods will assure that lightweight grippers in the future, which are made of composites, will take root in the automotive industry. In this example SCHUNK currently presented a long-stroke gripper made of carbon fiber composites with a scalable pneumatic drive. The lightweight scores in energy efficiency and in cost effectiveness. At a weight of 10 kg, the LEG-C disposes of a gripping force of up to 4,000 N and a variable stroke of up to 600 mm. If shortened finger travels are required, the stroke can be individually scaled. This minimizes the cycle times and reduces the compressed air consumption, which makes the gripper much more efficient. For offering a continuous lightweight concept, the aluminum fingers are also executed in a lightweight design. They travel on recirculating ball bearing carriages. Via the quantity and the distance between the guiding carriages, the gripper can be exactly adjusted to the individual payload. In case of particularly high gripping forces or extremely long fingers, the distance between the carriages is enlarged. This way, even fingers with a length of more than 1,000 mm can be used. The scope-free belt drive and the synchronized fingers assure that the gripper is working precisely at variable strokes. This is ideal when large and small parts have to be alternately handled. Figure 3

Talented Gripper Hand
In the automotive industry there is a high need for the flexible gripping of various small components, thereby the human hand is surely the best template. The SDH-2 three-finger gripper hand from SCHUNK is structured similarly. With its seven independent degrees of freedom, it can grip and position various objects without having any setup times. The gripper hand dominates in the industrial gripping types “three-finger centric,“ “two-finger parallel” and ”cylindrical gripping,” and many other versions. A tactile sensor system safely and sensitively monitors the optimum grip and supplies information to the control unit in order to do gripping corrections if necessary. Therefore, even difficult geometries can be reliably handled, positioned, or inserted. For industrial applications, the SDH-2 is protected against dust and moisture. Figure 4

Functional Assembly Groups
Automating plants in the automotive industry are becoming more complex and have a more compact performance, while at the same time cost pressure is continuously increasing. Customer-specific functional assembly groups from SCHUNK show how successful this balancing act can be. They combine cost and time advantages of standard components with benefits in productivity and processes of individual special solutions. The result is the highest possible level of process reliability in manufacturing and operating the plant. Moreover, the assembly groups reduce development times and increase the security in planning. Figure 5

The medium and long-term development of the automotive industry will lead to highly flexible manufacturing units that do not need any rigidly defined tools, devices, or gripping systems Figure 6. Therefore, manufacturing one-piece series should become more economic in future with more-complex, multifaceted, sensor-equipped gripping, and handling systems will be available that will be freely programmable and easy to integrate. Concerning retooling, these all-rounders will become reusable components that can be used in new or modified processing lines repeatedly.