Force5 Single Station Simulator

The AMTI Force5 is a multi-purpose multiaxis testing machine ideal for biomechanics research and testing laboratories. Standard systems include 2-DOF, 4-DOF and 5-DOF (degrees of freedom) configurations. Auxiliary hydraulic ports and spare servo-control channels enable the user to extend the machine to control up to eight independent motion and or force actuators.

The 2-DOF configuration includes a vertical translation actuator and a rotary actuator acting about the vertical axis. This configuration is well suited for biaxial fatigue testing and biaxial wear tests of materials and components. AMTI’s flexible control software facilitates a wide variety of testing scenarios such as: ramp and hold creep and stress relaxation tests; cyclical fatigue and wear tests using sine, square, triangle, saw-tooth and user defined waveforms; and monotonic constant strain and constant stroke stress-strain tests. The flexible control system permits the selection of force or displacement modes of operation providing greater versatility then found with conventional load frames.

The 4-DOF configuration is an ideal machine for laboratories involved in joint simulation and prosthetic joint design, research and testing. This configuration provides a vertical translation actuator and rotary actuator acting about the vertical axis. It also provides a horizontal translation actuator and horizontally aligned rotary actuator oriented at right angles to the horizontal motion. The instant center of rotation of the horizontal rotary actuator is mechanically coupled to the horizontal translation actuator. The 4-DOF configuration enables the simulation of the intra-articular motions of many of the body’s less congruent joints such as the knee, the temporomandibular joint, the glenohumeral joint which, during rotation, undergo a considerable translatory component. The 4-DOF system may be configured for knee simulation by use of AMTI’s tibial tray design which provides two additional degrees of freedom, which passively simulate medial-lateral translation and varus-valgus rotation of the knee joint.

The 5-DOF configuration provides an additional rotational axis corresponding to abduction-adduction of the hip. In this configuration the motions of high-conformity ball and socket joints like the hip may be simulated. This configuration provides three rotational motions with congruent rotational origins. The two translational axes of motion may be used to impose compression-distraction force as well as shear force on the joint structure.

Extensibility is built in to the Force5 machine. A rigid load frame arrangement allows you to conduct conventional stress-strain and fatigue tests as you would on a traditional load frame. Jaws, chucks and fixturing are available to facilitate these tasks. The Force5 is equipped with spare hydraulic ports that may be used to drive additional user supplied actuators which may be mounted on several bolt ready surfaces of the machine. AMTI’s flexible digital control system and NetControl software allow you to program and control up to eight channels of motion or force while spare analog inputs make it easy accept additional feedback control signals.

Force5 -- Degrees of Freedom
Configured for 2 DOF (load frame configuration)	Configured for 4 DOF (standard knee configuration)	Configured for 5 DOF (with hip abduction actuator)

The figures to the right depict the Force5 configured for knee and hip simulation (left to right). For knee simulation the machine provides four controlled degrees of freedom and two free degrees of freedom. The controlled DOF’s are compression-distraction, flexion-extension, internal-external rotation and anterior-posterior translation. For hip simulation, an additional actuator is mounted on the flexion actuator to accommodate abduction-adduction of the hip.

Features

Long life hydraulic actuators with hydrostatic bearings and laminar seals.

Six component load cell which measures Fx, Fy, Fz, Mx, My, and Mz.

Software selectable force or position control on appropriate axes.

Built in hydraulic power supply, filter and reservoir.

Includes a 39 channel Ethernet data acquisition system.

Powerful DSP based digital PID controller.

Includes computer, Ethernet interconnection and NetControl software.

Simulate the hip, knee and other joints.

Component testing.

Machine control and data acquisition

The Force5 machine is delivered with a complete data acquisition and control system. The Force5’s flexible control scheme allows the user to independently program the motions (or forces) for each of the controlled degrees of freedom to simulate physiological functions such as walking, running and stair climbing. The control architecture utilizes a DSP (digital signal processor) built into the machine to perform time critical tasks. The onboard DSP provides eight channels of waveform generation and implements eight channels of PID (proportional, integral, and derivative) control to drive the machines actuators. The DSP also manages the acquisition task by multiplexing between 23 channels of analog signals and measurements and by acquiring and assembling data to be delivered to the supervisory PC. The DSP communicates with AMTI’s NetControl software running on the supervisory PC via a simple, single cable Ethernet link.

The PID control loop algorithm is a standard form implementation providing proportional, integral and derivative feedback control with user adjustable parameters Kp, Ti and Td. Each channel is independently adjustable and entire sets of parameters governing all of the channels may be saved as user named files for the purpose of documenting and repeating a particular test or experimental setup.

Control loop feedback signals are digitized at a sample rate of 2000 samples per second per channel providing a control loop bandwidth of better then 100 Hz (hydraulic and mechanical considerations practically limit the band width to about 20 Hz). The digitized control signals are software mapped to the DSP’s eight channel PID loop feedback inputs. This provides the flexibility for the user to choose either force control or displacement control modes of operation by simply selecting the desired feedback channels (where appropriate). The PID loop’s set point inputs are provided by an eight channel, internal 256 point arbitrary waveform generation and interpolation algorithm. The PID loops calculated control signals are converted to analog signals at a rate of 2000 samples per second per channel and output to the systems servo valves as ±10 volt signals.

In addition to the 15 channels of high speed data acquisition used for the feedback control system a 200 sample per second data acquisition system is implemented to monitor 8 channels of analog signals such as temperatures or other user supplied inputs.

The NetControl software running on the supervisory PC provides the user with a complete operating interface for the Force5 machine as well as many powerful motion programming and data acquisition tools.

Several different “control panels” are available which facilitate different operating tasks. A “tuning” panel allows the user to adjust the PID control parameters to optimize performance while running different user supplied or canned waveforms. This allows the user to optimize the machines performance to achieve very close agreement between the driving waveforms and the resulting force and motion profiles. A “manual” panel allows the user to jog the machines actuators for the purposes of setup and sample insertion and extraction. In this mode canned (sine, square, triangle, ramp) and arbitrary waveforms may be downloaded and run for evaluation (and testing) without creating a full control program. NetControl’s “simulator” control panel allows the user to select and run preconfigured programs which automatically schedule waveform activities, data acquisition activities and present on-screen gages and controls to monitor the machines activities.

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Force5 specifications

Force5 Specifications
Item	Specification	Comment/condition
DOF
Vertical load	±4500N(±1000lb)	±25 mm (±1 inch)
Flexion extension	±100 degrees	45 N-m (400 in-lb)
IE rotation	±100 degrees	45 N-m (400 in-lb)
AP Translation	±25 mm (±1 inch)	±4500N(±1000lb)
Hip configuration
Abduction	±9 degrees	5 N-m (44 in-lb)
Knee configuration
ML Translation	±10 mm	Tibial tray, not controlled
Valgus rotation	±3 degrees	Tibial tray, not controlled
Actuator type
Vertical load	Servo-hydraulic
Flexion extension	Servo-hydraulic
IE rotation	Servo-hydraulic
AP Translation	Servo-hydraulic
Abduction	Brushless servo-motor	Removable abduction head
Control feedback	Typical	Alternate
Vertical load	Fz load cell	Position sensor
Flexion extension	Position sensor
IE rotation	Position sensor	Mz load cell
AP Translation	Position sensor	Fy load cell
Load cell
Channels	6 DOF	Fx, Fy, Fz, Mx, My, Mz
Type	Strain gage	Amplifier included in controls
Physical specifications
Length	86 cm (34 in)
Width	66 cm (26 in)
Height	180 cm (70 in)
Weight	550 kg (1200 lbs)
Hydraulic system
Type	Integral pump and motor	Included with machine
Pressure	800 psi	Constant pressure
Capacity
Installation
Power	240 VAC, 7 kva	3 phase, 50/60 Hz
Cooling	5 hp (3.7 kW)	1 gpm (4.2 L/m) - 60 ºF (16 ºC)

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Advanced Mechanical Technology, Inc.

Phone: 1-617-926-6700