Introduction
Bergmans Mechatronics LLC developed the software and the majority of the electronics for a prototype medical device under contract from a client in Irvine, CA in 2010. The final goal of this client is to produce a device which can automatically process various chemicals and bodily fluids over a period of several hours as part of a daily patient therapy regime. The present prototype serves as a functioning device which is being used for proof-of-concept laboratory (non-animal and non-human) testing and marketing demonstrations.
Actuators and Instrumentation
A number of actuators are incorporated into the system. Four gear motors located in the base of the device actuate valves within a removable cassette mounted to the top of the base. Three stepper motors in the base drive rollers which press against flexible tubes in the cassette. This combination of rollers and tubes forms three peristaltic pumps which enable fluids to be transported throughout the system. Two AC-powered heating pads heat fluid in two separate tanks and a UV lamp sterilizes an external port which accepts a tube leading to the patient.
Instrumentation in the system includes four thermistors, six pressure transducers and a unique, low-cost, aqueous ammonia monitor.
Electronics Hardware
The electronics hardware used to monitor and control the device consists of two main subsystems. The first is a PC-104 stack formed by four boards:
The second subsystem is a two-board stack of custom PCBs designed by BML. One of these PCBs is the “Instrumentation” board for instrument excitation power and signal conditioning. The second PCB is the “Power” board which hosts three solid state relays and headers for components controlled by the mechanical relays.
Future device improvement plans include adding the capability to provide aural notifications to the patient and to transfer log data to a USB memory device. To support these plans, the front panel of the device features a Language Selector knob and USB port. Neither of of these capabilities are currently implemented; therefore, the knob and port are not functional at the present time.
Software
The system software is written in C and operates within the Ubuntu Linux OS installed on the CompactFlash drive of the CPU board. This software features two modes of operation. The first is “Demo” mode in which the system will turn pump motors and valves over a one-minute period to illustrate the basic functions of the system.
The second operating mode is “Run” mode which is the normal, several-hour long, fluid processing mode for the device. In Run mode the valve positions and pumps are automatically controlled by a combination of instrumentation thresholds and a pre-programmed schedule.
Notable functions which are activated during this mode include:
- two closed-loop fluid temperature control systems
- monitoring of select pressures levels for indications of filter blockages or leaks, and depending on conditions, triggering a process pause or abort
- monitoring of the aqueous ammonia monitor output and triggering a process abort if excessively high levels are detected
In addition, Run mode performs a number of system configuration checks prior to beginning the main processing cycle. These checks include confirming that the cassette and the main fluid tanks are in place, and ensuring that fluid levels in the main tanks have been filled to the proper levels.
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