5 Steps to Designing Linear Actuators for Medical Devices
Although the term “linear actuator” can be defined broadly as any mechanical device that converts energy into controlled, straight-line motion, the definition narrows in the context of devices used for medical treatment and biomedical/chemical research. These types of linear motion applications require smooth motion, efficiency, accuracy, precision, and prolonged continuous or high-speed movement. The term refers to a new generation of precision-engineered lead screws, acme screws, and linear motion mechanisms, like those manufactured by Helix Linear Technologies.
Medical device applications range from simple tasks to more sophisticated challenges that require more significant force, speed, and control. The hospital bed adjustment mechanism is an example of a simple actuator application. At the same time, syringe pumps (small infusion pumps that are used to gradually administer intravenous medications to patients or control the administration of small amounts of fluids as part of laboratory research) are more complex.
The specific type and size of actuator that a design engineer needs depends on the nature of the application. The innumerable combination of stroke sizes, speeds, voltage, and types of these actuators are seemingly endless. Follow these five steps to design the proper actuator for your medical device needs.
Step One – Basic Specifications
Understanding the basic specifications for the load, actuator, power, and control required by your application is critical. Your first step toward selecting the proper actuator and weeding out unsuitable solutions is to determine:
- Energy source – How will you drive your actuator? Will your power come from an electric motor, pneumatic, hydraulic, mechanical, or piezoelectric source?
- Force requirements – How much force is necessary for your application, and in what direction will the load need to move?
- Speed – How fast will your actuator need to move?
- Distance – How far does your actuator need to travel? In other words, what is the stroke length?
- Duty cycle – How frequently will the actuator operate, and how much time will elapse between strokes.
- Environmental factors – What environmental factors (e.g., temperature variations, moisture, vibration, etc.) will affect operation?
Step Two – Evaluating Options
Once you’ve researched the basic specifications of your application, you’ll need to evaluate the various application- and actuator-specific options and how they apply to your situation.
- How will you mount the actuator within the device?
- Does the application require manual operation as a safety precaution?
- Are you working with limited space and need to fit a specific actuator footprint?
- If you are using an electric motor, what type and at what voltage?
- Does the application require feedback in terms of the speed force and/or position?
Step Three – Assessing Power Needs
The next step is to assess your mechanical and electrical power needs. Once you know the force your application needs, you will calculate the amount of electrical power required to generate the mechanical power you need.
Step Four – What’s the Duty Cycle?
The next step of establishing the duty-cycle factor is crucial. You may have decided upon an actuator that seems suitable through all of the previous steps, but it may ultimately fail because the duty-cycle limits are exceeded. The duty cycle indicates how often the actuator will operate and the time elapses between strokes. This is a critical contributing factor to heat generation and dissipation in a linear motion system. The component with the lowest allowable temperature establishes the duty-cycle limit for the entire system.
Step Five – Balancing Efficiency with Life Expectancy
The last step in selecting the suitable actuator for your application is balancing the device’s life expectancy and efficiency. Having both wears out simultaneously is preferable to replacing the actuator, which can be challenging in many medical applications.
Helix Linear Actuators Drive Medical Device Applications
Helix Linear Technologies has knowledgeable, experienced professionals that can help you progress through these steps, as well as a complete line of advanced precision-engineered lead screws, Acme screws, and linear actuators for your medical device applications.