Most robotic grippers are made using soft plastics – to pick up objects without damaging them – which melt at high temperatures, or hard and expensive metals. A team of researchers from the National University of Singapore (NUS), along with colleagues from Northeast Forest University, have developed a robotic wooden gripper that can be used in extreme temperatures but remains sensitive.
A wooden appliance made of wood also has other advantages – it is controlled by changes in humidity, temperature and lighting of the environment, thus reducing energy consumption.
Wood is highly engineered, naturally bent, available in large quantities, and inexpensive. In our latest work, we have shown that robotic grippers made of wood can overcome the limitations of human exercisers,” said Associate Professor Tan Swee Ching, who leads the research team from the Department of Materials Science and Engineering under the NUS College of Design and Engineering.
He added, “Our wooden robotic handle can stretch and bend itself due to moisture, temperature and stimulation. It also has good mechanical properties, which can be easily bent, high working temperature, low production cost, and it is biocompatible. These special features distinguish it from some old ways.”
The wooden handle opens when there is high humidity (above 95% RH), and closes tightly when the ambient temperature exceeds 70 deg C or when exposed to sunlight.
The research team published their findings in the online version of the scientific journal Advanced Equipment on 26 February 2023.
A wooden handle that is sensitive to moisture, heat and light
The researchers created a wooden wooden handle using pieces of Canadian maple wood that are 0.5 mm thin. Wood chips were first processed with sodium chloride to remove lignin – a component found in plant cell walls. The large holes in the wood are filled with a polymer called polypyrrole so that the material can absorb heat and light more easily.
The group also developed a nickel-based hygroscopic gel to absorb moisture. One side of the modified wooden pieces was coated with a moisture-retaining gel. A hydrophobic film was attached to the other side. This wet-dry difference allows the wood to quickly absorb water vapor on one side, and this accelerates the change in the shape of the wood composite when exposed to high humidity.
The wooden pieces are made to handle at 70 deg C using special moulds. When placed in a place with 95% RH (eg, humidity stimulation), the hygroscopic gel absorbed the moisture and the wooden handle was stretched and opened slowly to the outside.
“When exposed to high temperatures of over 70 deg C (heat stimulation), the wooden handle began to bend inwards and become more bent at 200 deg C.” explained Ms. Bai Lulu, a doctoral student in the NUS Department of Materials Science and Engineering and first author of the paper.
The group also tested the wooden handle under different forces, with a hydrophobic film facing the starting point. After the light increased the surface temperature of the gripper to about 42 deg C, the moisture gel began to lose water and the grip began to curl inward before reaching a curl of about 57 deg C.
The wooden handle remained stable after 100 driving cycles, demonstrating its stability and durability for long-term use.
Raising things at high temperatures
“We also confirmed the performance of the wooden handle when carrying objects at high temperatures. In our tests, the wooden handle successfully lifted a weight of 200 grams (equivalent to a can of soda) at about 170 deg C. This is not possible for most manufacturers made using soft polymer. “Depending on its structure, the wooden handle can carry a load 10,000 times higher than the weight of the handle,” said Professor Chen Wenshuai of Northeast Forest University and co-author of the research paper.
Next steps
Asst Prof Tan and his team are now looking to improve the performance of the wood, such as shortening the bending time from about 2 minutes at present, increasing the weight it can carry, and handling objects of different shapes and sizes. They are also finding ways to reduce costs and improve woodworking skills.
With its design and performance improvements, the team hopes to develop a wooden control system to assist firefighters in rescue operations.
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