Force plate nodes

You manage the connection and configuration settings for supported force plates included in your Vicon system architecture with the appropriate force plate node. You select the required force plate node under the Devices node in the System Resources tree. If no analog source is selected, [No Source] is displayed after the device type. Force plate data can be acquired through the analog capture functionality of a Vicon Lock Lab with an analog card.

For information about configuring force place display options, which affect the way force plates are displayed in the 3D Perspective view, see Configure force plates in the Vicon Nexus User Guide.

For information on how to handle cross-plate foot strikes when modeling with Plug-in Gait, see in the Vicon Nexus User Guide.

Force plate node context menu

You can select the following commands from the context menu displayed when you right-click on a force plate node:

Command	Description
Foot Contact	Attributes the force plate to: Auto-detect, in which Nexus attributes the force plate contact based upon foot segment kinematics Left foot contact Right foot contact Invalid if no valid left or right foot contact can be associated with the force plate. You can also adjust these settings by right-clicking a displayed force plate in the 3D Perspective view pane.
Show Raw	Adds each raw voltage signal for the device. For example, Kistler force plates contain 8 input channels that are processed to yield a resultant force and moment (3 components each, 6 total). Using the Show Raw command, you can select one or more inputs and graph their raw data in a Graph view pane, allowing you to view, troubleshoot, or configure a monitor for the raw signals. If you use Show Raw and collect a trial, the raw voltages will be stored in the .x1d file, so you can view them in the offline trial as well as the force channels. If you save the trial, or export a .c3d file, when you load the trial the raw channels will be grouped together and designated within an Imported Analog Device. To remove the raw inputs from the System Resources tree, right-click on the force plate node and click Hide Raw.
Zero Level	Calibrates the force plate. This process eliminates any significant offset between the force plate's nominal output levels at rest and its theoretical zero level. Select this option if, after setting the force plates to the electrical zero level, small differences remain between the theoretical zero level and the observed output level. This option is also available in the General section of the Properties pane.
Remove Device	Removes the force plate entry from the System Resources tree.

Force plate properties

You can configure settings for force plates in the following sections in the Properties pane for force plates.

General section

For all force plates:

Property	Description
Name	A user-defined display name for the force plate. Default: Blank
Delay Compensation	The delay compensation value (in seconds). All devices have a delay compensation value which adjusts the synchronization offset between the device and the Vicon data. Analog data collected with a Vicon connectivity device should already be synchronized, so this value should be set at 0. Values can be set between -10 and 10. Default: 0

For all but Kistler force plates:

Property	Description
Calibration File	The force plate calibration file Nexus is to use. This file describes the forces plate's properties, such as its physical dimensions, output voltages, and crosstalk coefficients between each analog output. Nexus automatically displays some of these values as the default settings in the relevant properties for the force plates (for example, X Length, Y Length and Calibration Matrix). Use the Browse for a folder button to navigate to the folder containing the calibration file supplied by the force plates manufacturer. Then use the drop-down list button to select the desired file. Default: Blank
Calibration Matrix	Displays the size of the calibration matrix (e.g., 6x6 Matrix). Click the Edit Text button to display the Calibration Matrix dialog box, which shows the values supplied by the force plate manufacturer. If you do not have a calibration file for your force plate, contact the manufacturer for a replacement file or refer to the calibration information supplied in your force plate documentation. You can manually edit the values for each channel scale. If you manually enter the values, ensure that you use the correct input values to transform the voltages captured by the Vicon connectivity device's analog card to forces and moments. The sensitivity values you must specify depend upon the type of force plate as shown in Calibration matrix values. Default: Identified from calibration file specified in the Calibration File property
Zero Level	Resets the force plate voltage zero level. This process eliminates any significant offset between the force plate's nominal output levels at rest and its theoretical zero level. Use this function if after setting the force plates to the electrical zero level, small differences remain between the theoretical zero level and the observed output level. Click the Edit Text button to display the Zero Level matrix in which you can enter the required value to calibrate the force plate. Then click Apply, then click Close.
Correction Factor	The factor by which Nexus is to convert the values supplied from a force plate into the values it requires. Correction factor corresponds to a force plate's amplifier setting and is used along with the calibration matrix to convert raw Volts to Newtons. For an AMTI OR6 Series force plate: Forces: from Newtons per microvolt (N/µV) to Newtons (N). Moments: from Newton meters per microvolt (Nm/µV) to Newton millimeters (Nmm). The formula for calculating the coefficient ( K) is: K = 1000000/(Gain x Excitation Voltage) where both Gain and Excitation Voltage are established in the AMTI amplifier. Check the settings for your AMTI amplifier. Default: 25 (for an AMTI amplifier with a default setting of 4,000 Gain and 10V Excitation Voltage).
Force Threshold (N)	The threshold (in Newtons) identifying the noise floor value for calculated forces. Forces that do not exceed this magnitude are assumed to be too noisy and are clamped to zero. Values can be set between 0-50. This value is not affected by the value for Force Threshold that is set in the Options dialog box (see Visualize and record Force Threshold) in the Vicon Nexus User Guide. Default: 25

For Kistler (Internal amplifier) force plates only:

Property	Description
Sensitivities (mV/N)	Force plate sensitivity vector. Click the Edit Text button to display the Sensitivities (mV/N) matrix in which you can enter the required values in millivolts per Newton. Default: Identified on connection

Calibration matrix values

Supported Force Plate	Manufacturer Supplied Units	Nexus Required Units
		Force Channels	Moment Channels
AMTI Hall Effect Plate (AccuGait Series)	United States Customary (USC) units Supplied in manufacturer's .acl file.	lb/V	lb/V
AMTI Strain Gage Plate (BP Series and OR6 Series) (See following Note)	United States Customary (USC) unit matrix Supplied in manufacturer's .plt file and Sensitivity Matrix.	uV/Vex/lb	uV/Vex/in lb
Bertec	International System (SI) units Supplied in manufacturer's documentation.	N/V	Nm/V
Kistler (External Amplifier)	International System (SI) units Supplied in manufacturer's documentation.	pC/N	pC/N
Kistler (Internal Amplifier)	International System (SI) units Supplied in manufacturer's documentation.	mV/N	mV/N

Note
If you are connecting to AMTI OR6 Series force plates, Nexus expects the force plate calibration values from the USC matrix in pounds (lb) and Inch-Pounds (in-lb) as supplied by AMTI with recent plates. Some older AMTI OR6 Series plates, however, have their USC calibration matrix presented in units of Pounds and Foot-Pounds (ft-lb).
If the calibration matrix for your force plate is presented in units of ft-lb, you must convert the values to the required in-lb units.
To do this, create a copy of the calibration .plt file and in this copy, divide the values of the last three columns of the matrix by 12.
Save this modified calibration file and apply it to your force plate by specifying it in the Calibration File field.
If you enter the matrix values manually, first divide the terms in the Sensitivity Matrix by 12.
The force plate moments will then scale correctly.

Source section

Property	Description
Source	The Vicon connectivity device to which the physical force plates device is connected. From the drop-down list, select the correct one from the available analog option cards detected in your Vicon system architecture. Default: None
Gain (V)	The programmable gain (+/- volts) for the channel: 1.25 Volts, 2.5 Volts, 5 Volts, or 10 Volts. The gain voltages correspond to 8, 4, 2 and 1 gain values, respectively (e.g., a gain of 2.5 Volts means that the input signal will be multiplied by 4. Default: 10.00
Fill	Fills all input connections in the expected sequence, starting with the lowest unassigned pin, for the device selected in Source.
Clear	Clears the input connection setting from all pins.
Channel	The input connections from the device. After selecting the Source, select the source input from the drop-down list, or use the Fill button to automatically fill all the positions. AMTI AccuGait: FzA, FzB, FzC, FzD, FyAC, FxDC, FxAB, FyBD AMTI OR6 and Bertec: Fx, Fy, Fz, Mx, My, Mz Kistler: Fx (1+2), Fx (3+4), Fy (1+4), Fy (2+3), Fz1, Fz2, Fz3, Fz4 Default: None

Dimensions section

Property	Description
X Length (mm)	The length (in millimeters) of the x axis of the force plate. Default: Identified from calibration file specified in the Calibration property, if one.
Y Length (mm)	The length (in millimeters) of the y axis of the force plate. Default: Identified from calibration file specified in the Calibration property, if one.

Position section

Property	Description
X Position (mm)	The origin coordinate (in millimeters) for the X axis of the force plate in relation to the origin of the capture volume, as specified by the L-Frame when you perform the System calibration. Default: 0
Y Position (mm)	The origin coordinate (in millimeters) for the Y axis of the force plate in relation to the origin of the capture volume, as specified by the L-Frame when you perform the System calibration. Default: 0
Z Position (mm)	The origin coordinate (in millimeters) for the Z axis of the force plate in relation to the origin of the capture volume, as specified by the L-Frame when you perform the System calibration. Default: 0

Normally, the force plate origin is chosen by placing the calibration device on the desired corner of the force plate. In this case, the position offset is half the width and half the length of the plate. However, for other plates that did not have the calibration device placed on them during calibration, you must fully specify the coordinates of the center of the plate in relation to the capture volume origin.

Orientation section

Property	Description
X Angle Axis (deg)	Maps the x axis (in degrees) of the local force plate coordinate system to the global coordinate system specified for Nexus in the System Preparation tools pane. Default: 0
Y Angle Axis (deg)	Maps the y axis (in degrees) of the local force plate coordinate system to the global coordinate system specified for Nexus in the System Preparation tools pane. Default: 0
Z Angle Axis (deg)	Maps the z axis (in degrees) of the local force plate coordinate system to the global coordinate system specified for Nexus in the System Preparation tools pane. Default: 0

Origin section