AMTI Joint Motion Simulator Machines
AMTI’s hip and knee simulator machines are used by the majority of the worlds major implant manufacturers. Our simulator machines have been proven through billions of cycles of user testing and the resulting contributions to the state of the art of implant design and manufacture have been extensive. AMTI’s hip and knee machine designs have resulted from the collaborative efforts of our team of skilled engineers and medical experts preeminent in the fields of hip and knee arthroplasty.
A partial list of our simulator machine customers includes:
Zimmer
Johnson and Johnson
Sultzer
DePuy
Smith & Nephew
Precision Implants
Kyocera
Nakashima
Massachusetts General
Hospital
Scripps Clinic
BioMet
Mechanical
systems
Our simulator machines are designed for long life. Our customers report individual machines that have run over 200 million cycles with no end in sight. The main hydraulic actuators of AMTI’s simulator machines are designed with hydro-static bearings and laminar primary seals. This eliminates metal to metal contact and results in extremely low wear rates on the primary actuator components. The estimated life expectancy of the main actuators is in the order of 108 cycles. Other subsystems of the machines are designed for easy on site maintenance.
Software
and Controls
Our simulator machine control system is designed to be flexible and robust. A multi-tiered control architecture uses an embedded processor to perform the real time motion control tasks while high level supervisory functions and user interface are provided by software running on a PC. The software makes it easy to setup, control and document the testing process. User supplied waveforms control the machines actuators through their cyclical motion (or force) patterns. Multiple waveforms may sequenced by the software’s scheduling system to simulate a series of physiological activities. Data acquisition events may be associated with each waveform process to analyze and document the wear process.
New
directions
Beginning in March of 2003 AMTI’s simulator machines will be equipped with a new digital control system. The new control system is based on AMTI’s DigiControl which is an eight channel PID controller. The DigiControl unit is embedded in the machines electronic enclosure and communicates with a supervisory PC via a single Ethernet interconnection for both data acquisition and control communications.
The DigiControl implements eight channels of PID (proportional, integral and derivative) control digitally in DSP (digital signal processor) firmware. This gives our users the ability to tune the machines performance for specific waveforms and achieve much more accurate tracking of the machines force and motion profiles. A real time data display allows the user to view the waveform, feedback and control signals for each channel while “tweaking” the controllers Kp, Ti, and Td (proportional gain, integral time constant, and derivative time constant) parameters to optimize performance.
Perhaps the most important aspect of this change is that the new control scheme will allow us to implement both displacement control and master slave force control modes of operation for the anterior-posterior displacement and the internal-external rotation motions of the knee machine.
As new innovations come out of the research community AMTI will be able to incorporate them in our DSP firmware. Under development at the current time is a control algorithm that will provide compliance based control for knee AP motion. The compliance control algorithm will effectively implement a software spring with user programmable non linear spring constant. The spring will have a neutral position which can be controlled by flexion angle. Flexion angle may also be used to modify the spring constant.
Easier
tuning, better tracking performance.
Reduced
number of boards, connectors and components.
Flexibility
and future extensibility.
Software
spring with variable X0 and programmable non linear spring constant.
Do you need something
different
If you are involved in joint simulation but need degrees of freedom other then offered by our standard Hip Simulator, Knee Simulator or Force 5 machines please let us know. Given our experience in multiaxis testing and the array of actuators and control systems that we have designed it is likely that we will be able to modify or retrofit one of our current machines to suite your needs. Please contact our sales office and ask to speak with our simulator engineering staff.
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