Floor System overview and related network architecture 

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... system in this chapter ranks among the top three in most of the dimensions of the performance criteria. Although there are four systems with frame rates higher than ours, the sensing area and sensor resolutions of these systems are much lower than our system. This chapter is an extension of our previous paper (Rangarajan, et al, 2007a) based on (Rangarajan, 2007b). This section provides essential information on pressure sensors, modular design approach used in building the large area pressure sensing floor. Later this section dives in deeper to explain the specifics of the embedded floor hardware and floor control software. Floor control hardware used in AME Floor-II (Srinivasan et al., 2005) has been retained in AME Floor-III but however the microcontroller firmware has been optimized to achieve high frame rate and reduced latency. Hardware overview given in this section creates a solid foundation to explain the optimization techniques in section 4. Force sensing resistors have been used as individual sensor entities for AME Floor-III system. They are made up of pressure sensitive polymer between conductive traces on sheets of Mylar. As the name implies, these sensors exhibit a change in resistance when pressure or force is applied on them. The value of resistance is of the order of mega ohms under no pressure and drops to few kilo ohms when pressure is applied. Each pressure sensor element has an approximate sensing area of 6 mm x 6 mm and measure 10 mm x 10 mm including the non-sensing area. Such a small size paves way for dense aggregation of sensors in the sensing space thereby resulting in higher sensor densities. It is important to note that the force sensing resistors does not give very accurate measurements of pressure or force applied as there may be 15% to 20% variation between each other. Also they suffer from a property called creep or drift where the measured resistance values tend to slowly vary when subjected to constant pressure over a long period of time thereby inducing an error in pressure measurements. However force sensing resistors can be used very effectively for relative pressure measurements and acquiring pressure distribution data which serves the purpose of wide variety of applications such as medicine for diagnosis of various gait pathologies, automotive, robotics and interactive arts applications. Force sensing resistors are generally available in several shapes and sizes like sensor pads, two dimensional sensor array matrix, continuous force sensing strips or several other forms depending on the application. Pressure sensing mat is a dense aggregation of force sensing resistors forming a two dimensional sensor array matrix. Tekscan 5315 pressure mat consisting of 2016 force sensing resistors arranged in grid of 42 rows x 48 columns have been used for AME Floor-III design.The dimension of each pressure mat is approximately 62 cm x 53 cm with an active area of 48.8 cm x 42.7 cm .The sensor mat is rated at 30 pounds per square inch (PSI). There are 2016 sensors in an active area of 322.98 square inch giving sensor densities of about 6.25 sensors/square inch. Pressure sensing panel is constructed with eight such pressure sensing mats (Srinivasan, P., 2006). Eight Tekscan-5315 mats are arranged in 4 rows x 2 columns mounted on a wooden floor frame as shown in Fig. 1 (top right). Each pressure sensing mat has a non-sensing zone at the borders surrounding the active area. The pressure sensing mats are so laid and affixed on the floor panel in such a way that the active area of one mat overlaps the inactive area of another thereby avoiding such inactive zones (Srinivasan, P., 2006). Each pressure sensing mat has a connection tab where the pressure data of all the sensors collectively arrive. This connection tab passes through a slit on the front side of the panel and is back-folded to interface with hardware control board. Thus each panel has eight hardware control boards (one for each pressure sensing mat) mounted on the back side. AME Floor-III is constructed by assembling 12 such pressure sensing panels (explained above) in 3 x 4 panel matrix. Thus the entire floor consists of a total of 96 networked pressure sensing mats assembled in 12 rows x 8 columns as shown in Fig. 2 and spanning a total sensing area of 180 square feet (15 feet x 12 feet). Such a modular design ensures large sensing area while still maintaining smaller frames for ease of use and installation. Also modularity in design paves way for creation of floor of different shapes and sizes (walkways, dance floor) and easy reconfiguration to suit external environments. The related network architecture used in AME Floor-III is illustrated in Fig. 2. All the 96 pressure sensing units are assigned static IP addresses and they form a local private network. Each and every pressure sensing unit has an associated hardware control board with an ethernet interface. There are two layers of network switches as shown in the Fig. 2. Multiple switches in multiple layers are deployed to share the network load and ensure sufficient leeway so that network switches are not operating to its rated full capacity which in turn increases performance and life time. All the twelve pressure units in one column are connected to a single fast ethernet switch on the first layer by means of ethernet cables. In a similar fashion, all pressure sensing units in 8 columns communicate with the fast ethernet network switch of their respective columns. The output port of eight fast ethernet switches is wired to the gigabit switch on the second layer. The output of the gigabit switch communicates with the host computer running the floor control software viz. Floor Control and Visualization Engine (FCAVE). FCAVE collects the pressure data arriving from 96 different IP’s on 96 different ports and uses the source IP to identify and index the pressure data pertaining to different mats. The software further assembles all the 96 data packets (arriving from 96 mats) based on their location to create one large floor packet for each frame and sends it out to a multicast network. By this arrangement several ends users listening to the multicast network get access to the pressure data. The mechanical design and installation of AME Floor-III is implemented in three layers namely the sub floor framework, surface floor (shown in Fig 1) and marley layer. The sub floor framework forming the bottom most layer is constructed using long steel rails welded to form a grid like structure and mounted on wooden blocks. This layer serves as a raised pedestal for the entire floor giving an elevation of approximately 4 inches above ground and provides the required spring and resilience to prevent injuries due to user activity like falling, jumping etc. Also such a raised installation paves way for all the necessary interconnect, ethernet wiring, power distribution and cabling to be housed beneath the floor in a neat and coherent fashion. The surface floor is made of a solid wooden framework and made to rest on the sub-floor layer. This layer forms the solid rigid structure supporting the users on the floor system. The pressure sensing mats and the hardware control circuitry for data collection are affixed to the surface floor structure on the frontal and dorsal side respectively. The third and the topmost layer is sheet of marley which is a vinyl surface, covering the entire area of the floor. The marley serves two main purposes. Firstly it aids in protection of the sensor matrix which are easily susceptible to damage by sharp and pointed objects and thereby increasing the longevity of the sensors. Secondly, it provides the necessary friction and contact grip for the subjects thereby preventing slips and fall injuries. Marley surface is generally preferred over standard wood or tiled surface structures for better movement control and less slipperiness. The hardware control circuitry used in AME Floor–II (Srinivasan, P., 2006) has been retained in AME Floor –III but the microcontroller firmware has been optimized in AME Floor-III to achieve a higher frame rate. The floor hardware (Srinivasan, P., 2006) comprises of microcontroller, multiplexers, A/D converter and ethernet enabled rabbit controller which are all wired together on a hardware control board and collectively termed as ‘mat based controller’. The block diagram of the floor hardware (Srinivasan, P., 2006) is shown in Fig 3. The microcontroller (PIC18F6585) forms the heart of the mat-based controller which generates the timing and control signals for all the components on the hardware control board to coordinate and sequence their operation of scanning sensors and reading pressure values. It has programmable capabilities to synchronize the sensor scan based on an internal timer or from an external clock signal. The latter has been currently implemented whereby the scan of all 2016 sensors on a single mat are synchronized with the external clock from the motion capture system. This implementation paves way for temporal synchronization of AME Floor-III and motion capture system for multimodal sensing. At the onset of falling edge of the synchronization clock, the microcontroller initiates a sequential scanning process of 2016 sensors arranged in 42 x 48 matrix. The pressure sensors (force sensing resistors) indicate a change in resistance when pressure is applied. This change in resistance is converted to a proportional analog voltage by a simple resistor divider network. Signal multiplexing has been implemented using a bank of six CD74HC4067 16-to-1 multiplexers to read the pressure voltage signals. Three multiplexers are used for the row lines and three for the column lines of the sensor matrix and each input line of the multiplexer is wired to a single pressure sensor output. The microcontroller streams out the multiplexer selects signals in a sequence to read the pressure values from sensor 1 to sensor 2016 one ...

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... Also it showed preliminary multimodal integrable capabilities in temporal domain only and not spatial domain. To fully address these issues, we have developed an improved, ingenious and in- house pressure sensing floor system (AME Floor-III) described in this chapter and listed in the last row of Table 1. AME Floor-III system is characterized by large sensing area, higher frame rate, smaller latency, enhanced user friendliness, spatial and temporal integrability with motion capture system to create a multimodal environment, modular/scalable design thereby matching our ideal pressure sensing demands for real time movement based human computer interaction. Comparison with other systems reveals that our proposed system in this chapter ranks among the top three in most of the dimensions of the performance criteria. Although there are four systems with frame rates higher than ours, the sensing area and sensor resolutions of these systems are much lower than our system. This chapter is an extension of our previous paper (Rangarajan, et al, 2007a) based on (Rangarajan, 2007b). This section provides essential information on pressure sensors, modular design approach used in building the large area pressure sensing floor. Later this section dives in deeper to explain the specifics of the embedded floor hardware and floor control software. Floor control hardware used in AME Floor-II (Srinivasan et al., 2005) has been retained in AME Floor-III but however the microcontroller firmware has been optimized to achieve high frame rate and reduced latency. Hardware overview given in this section creates a solid foundation to explain the optimization techniques in section 4. Force sensing resistors have been used as individual sensor entities for AME Floor-III system. They are made up of pressure sensitive polymer between conductive traces on sheets of Mylar. As the name implies, these sensors exhibit a change in resistance when pressure or force is applied on them. The value of resistance is of the order of mega ohms under no pressure and drops to few kilo ohms when pressure is applied. Each pressure sensor element has an approximate sensing area of 6 mm x 6 mm and measure 10 mm x 10 mm including the non-sensing area. Such a small size paves way for dense aggregation of sensors in the sensing space thereby resulting in higher sensor densities. It is important to note that the force sensing resistors does not give very accurate measurements of pressure or force applied as there may be 15% to 20% variation between each other. Also they suffer from a property called creep or drift where the measured resistance values tend to slowly vary when subjected to constant pressure over a long period of time thereby inducing an error in pressure measurements. However force sensing resistors can be used very effectively for relative pressure measurements and acquiring pressure distribution data which serves the purpose of wide variety of applications such as medicine for diagnosis of various gait pathologies, automotive, robotics and interactive arts applications. Force sensing resistors are generally available in several shapes and sizes like sensor pads, two dimensional sensor array matrix, continuous force sensing strips or several other forms depending on the application. Pressure sensing mat is a dense aggregation of force sensing resistors forming a two dimensional sensor array matrix. Tekscan 5315 pressure mat consisting of 2016 force sensing resistors arranged in grid of 42 rows x 48 columns have been used for AME Floor-III design.The dimension of each pressure mat is approximately 62 cm x 53 cm with an active area of 48.8 cm x 42.7 cm .The sensor mat is rated at 30 pounds per square inch (PSI). There are 2016 sensors in an active area of 322.98 square inch giving sensor densities of about 6.25 sensors/square inch. Pressure sensing panel is constructed with eight such pressure sensing mats (Srinivasan, P., 2006). Eight Tekscan-5315 mats are arranged in 4 rows x 2 columns mounted on a wooden floor frame as shown in Fig. 1 (top right). Each pressure sensing mat has a non-sensing zone at the borders surrounding the active area. The pressure sensing mats are so laid and affixed on the floor panel in such a way that the active area of one mat overlaps the inactive area of another thereby avoiding such inactive zones (Srinivasan, P., 2006). Each pressure sensing mat has a connection tab where the pressure data of all the sensors collectively arrive. This connection tab passes through a slit on the front side of the panel and is back-folded to interface with hardware control board. Thus each panel has eight hardware control boards (one for each pressure sensing mat) mounted on the back side. AME Floor-III is constructed by assembling 12 such pressure sensing panels (explained above) in 3 x 4 panel matrix. Thus the entire floor consists of a total of 96 networked pressure sensing mats assembled in 12 rows x 8 columns as shown in Fig. 2 and spanning a total sensing area of 180 square feet (15 feet x 12 feet). Such a modular design ensures large sensing area while still maintaining smaller frames for ease of use and installation. Also modularity in design paves way for creation of floor of different shapes and sizes (walkways, dance floor) and easy reconfiguration to suit external environments. The related network architecture used in AME Floor-III is illustrated in Fig. 2. All the 96 pressure sensing units are assigned static IP addresses and they form a local private network. Each and every pressure sensing unit has an associated hardware control board with an ethernet interface. There are two layers of network switches as shown in the Fig. 2. Multiple switches in multiple layers are deployed to share the network load and ensure sufficient leeway so that network switches are not operating to its rated full capacity which in turn increases performance and life time. All the twelve pressure units in one column are connected to a single fast ethernet switch on the first layer by means of ethernet cables. In a similar fashion, all pressure sensing units in 8 columns communicate with the fast ethernet network switch of their respective columns. The output port of eight fast ethernet switches is wired to the gigabit switch on the second layer. The output of the gigabit switch communicates with the host computer running the floor control software viz. Floor Control and Visualization Engine (FCAVE). FCAVE collects the pressure data arriving from 96 different IP’s on 96 different ports and uses the source IP to identify and index the pressure data pertaining to different mats. The software further assembles all the 96 data packets (arriving from 96 mats) based on their location to create one large floor packet for each frame and sends it out to a multicast network. By this arrangement several ends users listening to the multicast network get access to the pressure data. The mechanical design and installation of AME Floor-III is implemented in three layers namely the sub floor framework, surface floor (shown in Fig 1) and marley layer. The sub floor framework forming the bottom most layer is constructed using long steel rails welded to form a grid like structure and mounted on wooden blocks. This layer serves as a raised pedestal for the entire floor giving an elevation of approximately 4 inches above ground and provides the required spring and resilience to prevent injuries due to user activity like falling, jumping etc. Also such a raised installation paves way for all the necessary interconnect, ethernet wiring, power distribution and cabling to be housed beneath the floor in a neat and coherent fashion. The surface floor is made of a solid wooden framework and made to rest on the sub-floor layer. This layer forms the solid rigid structure supporting the users on the floor system. The pressure sensing mats and the hardware control circuitry for data collection are affixed to the surface floor structure on the frontal and dorsal side respectively. The third and the topmost layer is sheet of marley which is a vinyl surface, covering the entire area of the floor. The marley serves two main purposes. Firstly it aids in protection of the sensor matrix which are easily susceptible to damage by sharp and pointed objects and thereby increasing the longevity of the sensors. Secondly, it provides the necessary friction and contact grip for the subjects thereby preventing slips and fall injuries. Marley surface is generally preferred over standard wood or tiled surface structures for better movement control and less slipperiness. The hardware control circuitry used in AME Floor–II (Srinivasan, P., 2006) has been retained in AME Floor –III but the microcontroller firmware has been optimized in AME Floor-III to achieve a higher frame rate. The floor hardware (Srinivasan, P., 2006) comprises of microcontroller, multiplexers, A/D converter and ethernet enabled rabbit controller which are all wired together on a hardware control board and collectively termed as ‘mat based controller’. The block diagram of the floor hardware (Srinivasan, P., 2006) is shown in Fig 3. The microcontroller (PIC18F6585) forms the heart of the mat-based controller which generates the timing and control signals for all the components on the hardware control board to coordinate and sequence their operation of scanning sensors and reading pressure values. It has programmable capabilities to synchronize the sensor scan based on an internal timer or from an external clock signal. The latter has been currently implemented whereby the scan of all 2016 sensors on a single mat are synchronized with the external clock from the motion capture system. This implementation paves way for temporal synchronization of AME Floor-III and motion capture system for multimodal sensing. At the onset of falling edge of the synchronization clock, the microcontroller initiates a sequential scanning ...

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... and temporal integrability with motion capture system to create a multimodal environment, modular/scalable design thereby matching our ideal pressure sensing demands for real time movement based human computer interaction. Comparison with other systems reveals that our proposed system in this chapter ranks among the top three in most of the dimensions of the performance criteria. Although there are four systems with frame rates higher than ours, the sensing area and sensor resolutions of these systems are much lower than our system. This chapter is an extension of our previous paper (Rangarajan, et al, 2007a) based on (Rangarajan, 2007b). This section provides essential information on pressure sensors, modular design approach used in building the large area pressure sensing floor. Later this section dives in deeper to explain the specifics of the embedded floor hardware and floor control software. Floor control hardware used in AME Floor-II (Srinivasan et al., 2005) has been retained in AME Floor-III but however the microcontroller firmware has been optimized to achieve high frame rate and reduced latency. Hardware overview given in this section creates a solid foundation to explain the optimization techniques in section 4. Force sensing resistors have been used as individual sensor entities for AME Floor-III system. They are made up of pressure sensitive polymer between conductive traces on sheets of Mylar. As the name implies, these sensors exhibit a change in resistance when pressure or force is applied on them. The value of resistance is of the order of mega ohms under no pressure and drops to few kilo ohms when pressure is applied. Each pressure sensor element has an approximate sensing area of 6 mm x 6 mm and measure 10 mm x 10 mm including the non-sensing area. Such a small size paves way for dense aggregation of sensors in the sensing space thereby resulting in higher sensor densities. It is important to note that the force sensing resistors does not give very accurate measurements of pressure or force applied as there may be 15% to 20% variation between each other. Also they suffer from a property called creep or drift where the measured resistance values tend to slowly vary when subjected to constant pressure over a long period of time thereby inducing an error in pressure measurements. However force sensing resistors can be used very effectively for relative pressure measurements and acquiring pressure distribution data which serves the purpose of wide variety of applications such as medicine for diagnosis of various gait pathologies, automotive, robotics and interactive arts applications. Force sensing resistors are generally available in several shapes and sizes like sensor pads, two dimensional sensor array matrix, continuous force sensing strips or several other forms depending on the application. Pressure sensing mat is a dense aggregation of force sensing resistors forming a two dimensional sensor array matrix. Tekscan 5315 pressure mat consisting of 2016 force sensing resistors arranged in grid of 42 rows x 48 columns have been used for AME Floor-III design.The dimension of each pressure mat is approximately 62 cm x 53 cm with an active area of 48.8 cm x 42.7 cm .The sensor mat is rated at 30 pounds per square inch (PSI). There are 2016 sensors in an active area of 322.98 square inch giving sensor densities of about 6.25 sensors/square inch. Pressure sensing panel is constructed with eight such pressure sensing mats (Srinivasan, P., 2006). Eight Tekscan-5315 mats are arranged in 4 rows x 2 columns mounted on a wooden floor frame as shown in Fig. 1 (top right). Each pressure sensing mat has a non-sensing zone at the borders surrounding the active area. The pressure sensing mats are so laid and affixed on the floor panel in such a way that the active area of one mat overlaps the inactive area of another thereby avoiding such inactive zones (Srinivasan, P., 2006). Each pressure sensing mat has a connection tab where the pressure data of all the sensors collectively arrive. This connection tab passes through a slit on the front side of the panel and is back-folded to interface with hardware control board. Thus each panel has eight hardware control boards (one for each pressure sensing mat) mounted on the back side. AME Floor-III is constructed by assembling 12 such pressure sensing panels (explained above) in 3 x 4 panel matrix. Thus the entire floor consists of a total of 96 networked pressure sensing mats assembled in 12 rows x 8 columns as shown in Fig. 2 and spanning a total sensing area of 180 square feet (15 feet x 12 feet). Such a modular design ensures large sensing area while still maintaining smaller frames for ease of use and installation. Also modularity in design paves way for creation of floor of different shapes and sizes (walkways, dance floor) and easy reconfiguration to suit external environments. The related network architecture used in AME Floor-III is illustrated in Fig. 2. All the 96 pressure sensing units are assigned static IP addresses and they form a local private network. Each and every pressure sensing unit has an associated hardware control board with an ethernet interface. There are two layers of network switches as shown in the Fig. 2. Multiple switches in multiple layers are deployed to share the network load and ensure sufficient leeway so that network switches are not operating to its rated full capacity which in turn increases performance and life time. All the twelve pressure units in one column are connected to a single fast ethernet switch on the first layer by means of ethernet cables. In a similar fashion, all pressure sensing units in 8 columns communicate with the fast ethernet network switch of their respective columns. The output port of eight fast ethernet switches is wired to the gigabit switch on the second layer. The output of the gigabit switch communicates with the host computer running the floor control software viz. Floor Control and Visualization Engine (FCAVE). FCAVE collects the pressure data arriving from 96 different IP’s on 96 different ports and uses the source IP to identify and index the pressure data pertaining to different mats. The software further assembles all the 96 data packets (arriving from 96 mats) based on their location to create one large floor packet for each frame and sends it out to a multicast network. By this arrangement several ends users listening to the multicast network get access to the pressure data. The mechanical design and installation of AME Floor-III is implemented in three layers namely the sub floor framework, surface floor (shown in Fig 1) and marley layer. The sub floor framework forming the bottom most layer is constructed using long steel rails welded to form a grid like structure and mounted on wooden blocks. This layer serves as a raised pedestal for the entire floor giving an elevation of approximately 4 inches above ground and provides the required spring and resilience to prevent injuries due to user activity like falling, jumping etc. Also such a raised installation paves way for all the necessary interconnect, ethernet wiring, power distribution and cabling to be housed beneath the floor in a neat and coherent fashion. The surface floor is made of a solid wooden framework and made to rest on the sub-floor layer. This layer forms the solid rigid structure supporting the users on the floor system. The pressure sensing mats and the hardware control circuitry for data collection are affixed to the surface floor structure on the frontal and dorsal side respectively. The third and the topmost layer is sheet of marley which is a vinyl surface, covering the entire area of the floor. The marley serves two main purposes. Firstly it aids in protection of the sensor matrix which are easily susceptible to damage by sharp and pointed objects and thereby increasing the longevity of the sensors. Secondly, it provides the necessary friction and contact grip for the subjects thereby preventing slips and fall injuries. Marley surface is generally preferred over standard wood or tiled surface structures for better movement control and less slipperiness. The hardware control circuitry used in AME Floor–II (Srinivasan, P., 2006) has been retained in AME Floor –III but the microcontroller firmware has been optimized in AME Floor-III to achieve a higher frame rate. The floor hardware (Srinivasan, P., 2006) comprises of microcontroller, multiplexers, A/D converter and ethernet enabled rabbit controller which are all wired together on a hardware control board and collectively termed as ‘mat based controller’. The block diagram of the floor hardware (Srinivasan, P., 2006) is shown in Fig 3. The microcontroller (PIC18F6585) forms the heart of the mat-based controller which generates the timing and control signals for all the components on the hardware control board to coordinate and sequence their operation of scanning sensors and reading pressure values. It has programmable capabilities to synchronize the sensor scan based on an internal timer or from an external clock signal. The latter has been currently implemented whereby the scan of all 2016 sensors on a single mat are synchronized with the external clock from the motion capture system. This implementation paves way for temporal synchronization of AME Floor-III and motion capture system for multimodal sensing. At the onset of falling edge of the synchronization clock, the microcontroller initiates a sequential scanning process of 2016 sensors arranged in 42 x 48 matrix. The pressure sensors (force sensing resistors) indicate a change in resistance when pressure is applied. This change in resistance is converted to a proportional analog voltage by a simple resistor divider network. Signal multiplexing has been implemented using a bank of six CD74HC4067 16-to-1 multiplexers to read the pressure voltage signals. Three multiplexers are used for the row lines ...