You usually ask someone to marry you when you are sure of yourself. After all, it's a marriage, the great love. In industrial robotics, things are admittedly a little less romantic, but here too, companies are asking themselves: How do I find the right person? In times when humans and robots work hand in hand, there are collaborative grippers for every possible aspect of industrial production. The market for robotic grippers and tools is growing unstoppably: according to the International Federation of Robotics (IFR), its global sales potential is set to quadruple to 1.4 billion euros by 2023. While the supply is increasing, the range of applications for such gripping tools is also expanding: sophisticated sensor technology and modern software give them the necessary sensitivity to even take on tasks in precision assembly or sensitive surface treatment. At the start of every automation project, the question of which gripper model is the right one arises more than ever.

Pick & place: bigger equals better?

Collaborative robot arms and grippers are typically used for pick & place tasks. These include palletizing, packaging and machine loading. The basic advantage of automating these tasks is that processes can be accelerated while maintaining constant performance, which increases productivity. In the food and pharmaceutical sectors, automation also reduces the risk of contamination.

Collaborative two-finger grippers are generally recommended for pick & place applications. Features such as individually adaptable fingertips or depth compensation make their use more efficient, as the grippers can adapt better to the task at hand and grip objects more precisely. In order to automate complex processes particularly efficiently, it also makes sense to use a double gripper: such models are able to handle two objects at the same time, which further reduces throughput times.

Grippers with integrated sensors are suitable for precision assembly: they are able to position workpieces precisely despite imprecise parameters. © OnRobot

Which model is the right choice in each individual case depends on the parameters of the object to be handled. For example, the gripper must be able to lift the respective weight and therefore be approved for a certain load capacity. The size and circumference of the object are also decisive. Grippers with a larger span are advantageous as they can adjust more flexibly to the circumference of the object. However, it is generally advisable to choose the smallest possible model that meets your needs. The heavier the gripper itself, the lower the available payload of the robot arm. Users also save costs, space and energy.

Vacuum gripper for flat objects

Vacuum grippers are particularly suitable for handling flat objects weighing up to around 10 kg. © OnRobot

In addition to weight and size, the shape of the objects to be handled is also decisive. If the objects are large and flat, a vacuum gripper makes sense. This is the case, for example, when handling solar panels, tiles or displays. In particular, models with adjustable arms and adjustable suction power are able to lift flat objects of different sizes and geometries. Models without an external air supply are also particularly space-saving and can therefore be integrated more easily into the production layout.

The adhesive Gecko gripper is suitable for handling flat objects with porous or perforated surfaces. © OnRobot

However, vacuum grippers have two disadvantages: firstly, their suction cups can leave marks on particularly sensitive surfaces. Secondly, it is not possible to create a vacuum on every surface, for example on porous or perforated structures such as drilled circuit boards. In such cases, adhesive gripping systems such as Gecko grippers provide a remedy. These are modeled on the biological structure of gecko feet: when their gripping surfaces, which are coated with tiny hairs, are pressed onto an object, van der Waals forces are generated that enable them to lift the object without delay. Slight, controlled tilting of the gripper releases the adhesion again. The special adhesion grippers are also suitable for users who are looking for an energy-efficient solution: they do not require electricity to maintain the gripping process. Which gripper makes sense in each individual case, however, is also determined by the required payload: Gecko grippers lift objects up to around 4 kg, whereas collaborative vacuum grippers such as the VG10 from OnRobot are also suitable for heavier loads up to around 10 kg.

Smart grippers for precision assembly

In precision and fine assembly, the challenge is often to precisely position delicate workpieces of different sizes and shapes despite imprecise positioning. This is the case, for example, when inserting pin connections. In the context of industrial production, robot arms often have to deal with soft, deformed materials or irregular workpieces. Nevertheless, they have to insert the pins into the narrow openings they contain.

Smart grippers such as the RG2 can dynamically adapt their grip to the respective workpiece. This makes them suitable for pick & place tasks. © OnRobot

To achieve this, the devices must be able to detect even the slightest resistance in order to correct their course in real time. Smart grippers with integrated sensors and corresponding software are particularly recommended for this purpose: They can feed the process data recorded by the sensor directly back to the robot arm and adjust its movement without delay. This enables them to carry out precise assembly processes without knowing the exact parameters in advance.

The RG2-FT gripper from OnRobot, for example, has an integrated proximity sensor and force/torque sensors in its "fingertips", enabling it to grip objects centrally and insert valves into cylinder heads or mount manual gearboxes, for example.

Quality control requires sensitivity

Quality control also requires a high degree of flexibility, as grippers are regularly confronted with objects of different sizes. In addition, these are often sensitive, such as sample vials. Only with the right sensor technology, such as force-torque or proximity sensors, is the gripper able to adjust the pressure applied in such a way that the object in question is not damaged. The measurement of forces can also be automated cost-effectively using haptic sensors, which is relevant when testing plug connections, for example.

With this in mind, two-finger grippers with integrated sensors or in combination with a corresponding sensor module are also primarily suitable for quality inspection. The following generally applies to the location of the sensors: if the robot arm has to memorize complex motion sequences in the course of its task, a model in which the sensors are installed between the arm and gripper is advisable. A gripper with integrated sensors is particularly advantageous if it is to perform precision tasks such as fine assembly. If higher forces are expected in the process, a gripper with an external sensor is recommended, as the integrated sensors are more sensitive.