Testing for robotics design

A humanoid robot is being developed at the School of Engineering and Advanced Technology, Massey University, New Zealand, for implementing and evaluating dynamic gait algorithms.

Force sensors are placed on the bottom of the feet of the robot to provide feedback for the control system. The use of resistive force sensors is being investigated as an inexpensive and lightweight alternative to multi-axis force/torque sensors. 

However, resistive force sensors have a more limited accuracy and response time. Sensors from three companies have been tested: Sensitronic, Interlink, and Inaba Rubber. 

The sensors were tested with a TA.XTplus texture analyser, which is capable of applying specific forces at different rates. The sensors were tested for repeatability of response, drift, and response time to both application and removal of the force. An inverting op-amp is used to convert the force measurement of the sensor to an output voltage, which is read by an oscilloscope.

The force measurements from the texture analyser and the voltage output from the oscilloscope are recorded digitally. The data obtained from the measurements is analysed and the potential uses and limits of the sensors as feedback mechanisms in a bipedal humanoid robot are being determined.

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Applying the Texture Analyser to other Robotic Developments

At the Robotic Mobility Group, Massachusetts Institute of Technology, work was carried out at an earlier date on ‘A controllably adhesive climbing robot using magneto-rheological fluid’ using a TA.XTplus Texture Analyser.

Many cleaning and inspection tasks on buildings, towers, or large machinery are hazardous or difficult for humans to perform. Climbing robots could reduce the danger, but any adhesion mechanism utilised in real-world scenarios must be capable of traversing uncertain, dirty, and varied surfaces such as glass, acrylic, brick, concrete, or wood. Robotic adhesion mechanisms have taken inspiration from biology (via nano/micro adhesion inspired by geckos) or non-biological methods (e.g. sticky paddles extending from wheels) but have been compromised by the requirement for soft or rough surfaces for adhesion or the need for continual replacement of tape. 

The concept of adhesion based on magneto-rheological fluid is unique in that it can potentially be applied to a wide range of surfaces and yield large clamping pressures without needing a ferrous substrate or a large power supply.

The novel adhesive effects of magneto-rheological fluid for use in climbing robotics were experimentally measured and compared to existing theoretical models. Contrary to these models, the fluid thickness between two parallel plates was found to have little effect on the adhesive failure strength and a positive effect on time to failure. Target surface roughness was found to have a detrimental effect on pull-off adhesion and a positive effect on shearing loads. 

With the aid of adhesion measurement using the Texture Analyser, a robot capable of adhering to ceilings was designed and shown to be capable of holding 7.3 kPa of adhesive stress in both shear on rough vertical surfaces and normal force on glass sheets, demonstrating a novel form of adhesion on a wide range of surface roughnesses and orientations.

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The stories in this post are a small illustration of the wide range of industries in which Texture Analysis is becoming an indispensable aid to research and development. For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

The TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.

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