Biomedical Engineering Reference
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Force sensor
locations
Tile
surface
30 cm
30 cm
Fig. 17.7 Left diagrammatic view of the interface. Sensing and actuating components are integrated
beneath the floor. Right view from above showing sensor locations
17.4 Case Study: A Distributed, Multimodal Floor Interface
In this section, we review a case example, consisting of an interface developed by the
authors [ 39 ]. The interface is a modular collection of rigid floor components, each
of which is instrumented with force sensors and a large vibrotactile actuator. The
prototype shown in Fig. 17.7 comprises a square array of 36 tiles, with an area of
approximately four square meters. The floor is coated in reflective projection paint,
and a redundant pair of overhead video projectors is used for visual display, the visual
redundancy making it possible to reduce the effect of shadows cast by users.
The individual tile interfaces are rigid plates with dimensions 30
2cm,
supported by elastic vibration mounts, and coupled to a vibrotactile actuator (Clark
Synthesis, model TST229) beneath each plate [ 36 ]. Actuator signals are generated
on personal computers, output via digital audio interfaces, and amplified.
Normal forces are sensed at locations below the corner vibration supports of each
tile using a total of four resistive force sensors (Interlink model 402 FSR). Analog
data from the force sensors is conditioned, amplified, and digitized via a set of
32-channel, 16-bit data acquisition boards based on an Altera FPGA. Each sensor is
sampled at a rate of up to 1kHz, and the data is transmitted in aggregate over a low-
latency Ethernet link. An array of six small-form-factor computers is used for force
data processing and audio and vibrotactile rendering. A separate, networked server
is responsible for rendering visual feedback and managing user input (Fig. 17.8 ).
.
5
×
30
.
5
×
17.4.1 Contact Localization
For processing sensor data acquired through the distributed floor interface, the authors
applied intrinsic contact sensing techniques previously developed in the robotics
 
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