Pharmaceutical & medical
variety of sizes. The intended use of a pump will have a significant influence on its allowable size and power consumption. Size and power requirements are especially important as scientific equipment is increasingly being taken out of the lab and into the field, and as instruments are required to perform a greater number of tests within a smaller space. Stepper motor-driven pumps have size and
weight advantages over conventional syringe pumps. Also known as direct-drive units, stepper motor pumps use smaller motors and therefore consume less power than syringe pumps. This allows for further space savings by reducing the size of the pump and its power supply. Reducing power requirements also lowers the amount of heat generated by the pump, along with the cooling required. In some cases, cooling fans can be eliminated by using a pump with lower power consumption. Pump maintenance should also be a deciding
factor in medical instrument design. If a pump needs periodic maintenance, it should be in an easily accessible location within the system. The preferred location for a pump from a maintenance perspective may not be the most ideal fluidic location. A pump placed right next to the fluid supply offers the advantage of operating using short tubing runs but is not readily accessible for service. Pumps placed where the technician can easily get to them for service may require significantly longer lengths of tubing, often cutting down on system responsiveness. Selecting a pump that requires little or no maintenance may offer greater design flexibility.
The Lee Company
www.theleeco.com Common fluid CirCuits
While medical devices contain elaborate and sophisticated fluid circuits, they are often represented in the basic schematics shown below.
Circuit 1 shows a reciprocating pump using two 2-way solenoid valves: one on the inlet and one on the outlet. In this case, the pump is aspirating the fluid from a reservoir and dispensing to a point of interest. The dispense tip could also move, allowing multiple dispenses across titer plates, past detectors, or to waste. Alternatively, the circuit could use a 3-way valve on the inlet to allow the optional supply of a cleaning agent through the flow path.
Circuit 2 shows a piston pump operating with a single 3-way valve. The pump can aspirate a sample from one port of the valve and when the valve switches, the pump can dispense through the other port. Because this circuit only requires using one of the pump’s ports and a single valve, this is an easier circuit to drive. However, the valve’s internal volume may contribute to cross contamination of samples. Additional caution should be taken during valve actuation. As the valve switches, all three ports may be connected for a short period of time. During this switching, residual system pressures may lead to undesired flow.
InductIve SenSorS verIfy cannula SelectIon In robot-aSSISted laparoScopIc Surgery
R
obotic-assistance has started to be utilised in laparoscopic surgery but a key issue these systems face is ensuring that the correct length and diameter of cannula or trocar has been loaded into the robotic manipulator before insertion into the body cavity. To perform robot-assisted laparoscopic surgery,
the surgeon sits at a computer console viewing a 3-D image of the surgical field and guiding surgical instruments via joy-sticks. The improved depth perception and rotational movement provided by a robot has extended laparoscopic surgery to more complex procedures. These require cannulas of many different types, each individually identified by ridges and grooves machined into the area clamped by the robotic member. If the wrong cannula type is fitted it may be too
small for the tools required or too large for the intended procedure, with potential harm to surgical outcomes. It is therefore essential that the robotic system should check the cannula before allowing the surgeon to proceed with surgery. A non-contact solution is required. Space constraints around the robot also make small
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size essential. Contrinex’s ‘Basic’ range of inductive sensors (600 series), available from PLUS Automation, are installed into the clamping block of the robotic member and utilise their high-performance sensing capabality to detect the presence of machined ridges and grooves in the cannula. The groves provide a binary code that identifies the specific dimensions and profile of the cannula loaded. Detection is accomplished through the wall of the mounting block, isolating the sensors from the surgical device. Space constraints require these 6.5 mm diameter
sensors are mounted side by side with no spacing, essentially violating mounting rules. To avoid the possibility of cross talk or mutual interference the sensors are powered on and off sequentially and their output status monitored. Sensor data delivered to the control system allows
the surgeon to proceed with confidence that instrument movements within the patient’s body will be dimensionally correct and the internal size of the cannula is sufficient for entry of the surgical tools.
www.PLUSAx.co.uk
June 2021 Instrumentation Monthly
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