PLC+HMI enables critical stress testing

AeroSpec’s medical device test system simulates actual use to verify reliable operation of critical components.

By Bryan DeCelles and Zach Marinella, AeroSpec

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Medical devices used in hospitals and clinics around the world must undergo a series of rigorous tests to evaluate their reliability before coming into contact with patients. With the high stakes involving patient health, sometimes life-or-death situations, there is no room for mistakes or faulty devices. Each tool in a medical staff’s arsenal must function flawlessly every time.

With these demanding requirements in mind, AeroSpec, a custom equipment manufacturer in Chandler, Arizona, developed its medical device test system (Figure 1).

This system is designed to perform endurance tests on new medical devices to ensure high-quality performance when met with load and stress from actual use. The system helps medical device manufacturers run extensive tests to ascertain optimal designs, verify reliability and ensure robust products.

AeroSpec started as a machine shop more than 30 years ago and quickly evolved into a full-service custom equipment supplier for a variety of industries including automotive, semiconductor, medical and others. AeroSpec's OEM equipment provides customers with low-cost and efficient methods to verify their medical devices have been tested and are ready for use in the field, whether these devices will be used in a walk-in clinic or an operating room.

Initial design

The AeroSpec medical device test system is a cost-effective, pre-designed solution based around the IDEC FT1A PLC+HMI controller and operator interface unit. Versatility is a strength of the system, as it can be adapted to run tests on a wide variety of medical devices.

Using the PC-based programming software supplied with the PLC+HMI unit, AeroSpec developed a powerful program to control the unit, and a key feature of this design is the test system’s ability to operate lean assembly and testing fixtures.

AeroSpec began work on the test system based upon client-requested specifications. Their client needed a system to run endurance tests on the new product, a cosmetic surgery device used for cellulite reduction, with the ability to simulate the load on the product and measure the stress endured by the device.

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Initially, the request was for a test system that would measure current draw through the power cable of the tested device, but the client changed direction on the product to move to a wireless model, making the original request obsolete.

To comply with client requirements, AeroSpec opted to add an rpm sensor to measure and chart the change in velocity of the motor in the device. The rpm sensor would also provide the client’s engineers with critical data verifying the device could withstand real-world usage. This system was designed to allow AeroSpec’s client to run tests with wired devices, determine an optimal running current and copy that model to the wireless versions of the devices to continue testing.

Functionality and features

The test system is designed to execute endurance tests that assist medical-device manufacturers in the development of new products. The test system accomplishes this by simulating actual operating scenarios and by measuring the stress on the devices installed in the text fixtures to gauge how they perform (Figure 2).

The test system has three channels running in parallel with each other. When testing the endurance of medical devices, the test system controls and monitors three pneumatic actuators, three high-speed sensors that gauge rpm on the motor modules and three electromagnetic brakes. The brakes are used to simulate a load on the device, and the pneumatic actuators are used to activate and deactivate the devices.

The test system provides two main fault-condition alerts. The first condition—failed to activate part—occurs when the test system attempts to switch a device on and observes that the rpm reading from the motor module is not increasing. When this occurs, the test system tries to reactivate the device. If it fails to activate a device three times in a row, the test system provides a fault message. The second fault condition—failed to deactivate part— occurs when the test system attempts to turn off a device and doesn’t observe the rpm dropping to an acceptable level.

For both fault conditions, the test system flashes a red light for the station that failed to activate or deactivate a device. In a situation where one of the stations fails, or if the user attempts to initiate a cycle with the part incorrectly secured, the HMI screen will also display an alarm.

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