Force-sensitive SMA grippers using thermal activation

Industrial manipulators are central components of nearly all modern production facilities. They enable the precise handling of workpieces and tools. With increasing demands regarding speed, efficiency, precision, and installation space, the need for high-performance yet compact gripping solutions is growing. Conventional electromechanical or pneumatic grippers often reach their technical and energetic limits in these scenarios.

Electric drives usually require significant installation space, while pneumatic grippers require additional sensors and run counter to the trend of compressed-air-free production. Shape memory alloys (SMA) offer an innovative alternative here.

Properties and Functional Principle of Shape Memory Alloys

Shape memory alloys possess the ability to return to their original shape upon heating after an apparently plastic deformation. This is based on a reversible phase transformation, which makes SMAs powerful thermal actuators.

Key advantages of SMA:

• High power density with minimal installation space
• Low energy requirements
• Low-noise operation
• Easy integration into lightweight systems
• Integrated sensor effect through measurable resistance changes during phase transformation

The integrated sensor effect allows for the detection of external influences such as loads, stroke paths, or temperatures, as well as internal states like fatigue behavior. As a result, SMAs function simultaneously as both actuator and sensor.

Gripper Technology Based on Shape Memory Alloys

Gripping systems with SMA utilize electrically activatable wires that can be routed as flexibly as pneumatic lines. Control is achieved by measuring the electrical resistance, enabling precise management of movement and force behavior.

Performance features:

• Infinitely adjustable gripping force
• Exact fine positioning of the gripper jaws
• Forces up to 100 Newtons
• Gripping times under 500 milliseconds
• Service life of over one million cycles, depending on the design
• Easy scaling down to micro-grippers, for example in medical technology

Thanks to their compact design, SMA grippers are particularly suitable for sensitive handling tasks where low masses, precise positioning paths, and high repeatability are required.

Application in Injection Molding Automation

A double-acting, normally-open SMA gripping system was developed for gripping molded parts and removing sprues in injection molding automation. Due to the requirements for form-fit and force-fit removal, a modular approach was chosen.

Advantages of this modular concept:

• Flexible use as pincer or parallel grippers
• Direct adaptability of gripping force and stroke
• Easy transferability to different applications
• Compact design for confined installation spaces

Advantages Over Conventional Gripper Systems

SMA-based grippers offer several technical advantages over electromechanical and pneumatic solutions.

• Lightweight construction through functional integration – no need for additional sensors
• Compressed-air-free operation
• Electromagnetic compatibility and biocompatibility
• Scalable approach for diverse application scenarios