Miniature valves help to make robotic hand realistic

Citation

(2005), "Miniature valves help to make robotic hand realistic", Industrial Robot, Vol. 32 No. 2. https://doi.org/10.1108/ir.2005.04932bad.001

Miniature valves help to make robotic hand realistic

Miniature valves help to make robotic hand realistic

Keywords: Robotics, Valves (Electronics)

Imagine the essential requirements for the components used within a humanoid robot hand which is designed to replicate all the joints and movements of a human hand? Now imagine these components, for example, over 250 sensors, must be even smaller if the design is to be successful. When robotics get the human touch, size really does matter, and in this case the smaller the better.

The North London based Shadow Robot Company is an innovative British technology team breaking new ground in advanced robotic systems. These systems are used at the cutting-edge of research in robotics; ultimately these systems have the potential for producing the first humanoid domestic robots.

The systems developed by Shadow use “Air Muscles”, compliant non-linear pneumatic actuators, otherwise known as rubbertuators, McKibben muscles, or braided pneumatic actuators, and these offer important advantages for robotic systems. Their movement is similar enough to the movement of biological muscles to permit the construction of natural robots.

However, to achieve the same range of movements as the human hand demands large quantities of air muscles, 36 in all to control a total of 25 movements, and each air. Muscle needs two valves, one to fill and one to empty. This results in the need for 72 valves for each Hand. Since the Hand is to be used at the end of a robot's arm, standard pneumatic valves would have to be mounted off-board, resulting in significant cabling and control issues.

To improve the performance of the system, the muscles need to be placed in the same place as in the human – inside the forearm. In order for the valves to be located as close as possible to the muscles, they must be packed in at the elbow. This was a major challenge for the Shadow team. Eventually, miniature component specialists Lee Products were able to provide the solution, due to the ultra-compact size of their face-mount HDI valves (Plate 1).

Plate 1

The design of these valves enables Shadow to pack 72 valves into 1/30th of the space required by other valves. This allows the valves to be embedded directly into the dextrous hand itself, making a significant improvement in the quality and performance of the system. In the quest to pack the valves more densely, Shadow tried fitting an even smaller Lee plug-in HDI valve into the hand. However, the face-mount valve offers advantages in construction and maintenance, as well as allowing the use of a simpler and more modular manifold design.

Rich Walker, Technical Director at Shadow commented, “Most of the valves we looked at and tested were described as `miniature' although these were still at least as big as my thumb, however, the Lee plug-in valves were small enough to fit 72 into a cylinder 120 mm in diameter and 65 mm long”. He continued, “All of the other valves we tried were simply too bulky, the previous valve rig occupied a cubic foot of space and had to be mounted below the shoulder of the arm. This reduced our ability to control the hand, as well as making the robot arm non-portable”.

Summing up, Rich said, “We particularly appreciate the small size of the Lee valves, now the robot hand is self-contained, needing only an air supply and 28 V power and can be easily mounted on a robot or even carried around an exhibition”.

Lee HDI (LHD) series valves are designed on the three-way high density interface (HDI) valve platform and require only momentary (10 ms) pulses of current to switch the state. They consume only 28 mWs per switch and the polarity of voltage to the terminals controls the switched position. They are available in flexible plug-in configuration, so they are ideal for compact manifold applications. A one place ported adapter for use with 1/ 16in. tubing is available in addition to a variety of standard manifolds. The valves, which can be supplied in 5 and 12 V options and with other voltages available on request, have a flow capacity of 6 slpm and a pressure range of 0-15 psig.

Further details and product literature is available from: Lee Products Ltd. E-mail: sales@leeproducts.co.uk; and The Shadow Robot Company, London. Tel: +44 (0) 207 700 2487; E-mail: contact@shadow.org.uk; Web site: www.shadow.org.uk