Originally developed for audio speakers, voice coil actuation (VCA) technology is now being used to provide precise and reliable motion control for a wide range of applications. Even though it has been around for decades, VCA technology is still a mystery to many design engineers as until recently, the application spaces for which it was a cost-effective solution were relatively restricted. Many designers had to settle for more traditional, but less flexible, solenoid-based devices. Now that powerful MCUs and precise and efficient drivers are readily available, advanced linear motion designs using VCAs are easier and less expensive to implement.
VCAs offer many benefits: they are very simple and extremely robust, yet are as exactly precise as the input given them. VCAs accelerate smoothly and quickly to any position within their stroke with nearly zero hysteresis and are only limited by the system’s position-sensing precision and driver capability. Because of this accuracy, these devices lend themselves extremely well to applications such as medical devices, robotics, and industrial process equipment.
One application area that demands critical precision is the medical industry. Devices like drug-dispensing pumps do not work on approximations — every microlitre of liquid has to be carefully measured and managed. The precise motion control a VCA-based solution provides in a medical flow-management system increases accuracy without complexity or bulk.
The challenges in designing medical devices are compounded beyond strict performance and regulatory standards; there is also the need for small and lightweight devices to allow for portable use by caregivers moving room-to-room in a facility. This demand for performance in a constrained space lends itself well to a VCA solution.
Linear VCAs in particular can be designed to meet the ultra-small size and exacting motion control requirements needed in the medical industry. These tiny VCAs are often used to control inhalation and exhalation valves on ventilators to provide the exact amount of air specified and the necessary reliability for life-critical applications.
Another advantage with of these types of VCA motors are their bi-directional capabilities; permanent magnets, and magnetic latches, enable the VCA to remain in position at one end or the other of a stroke during a power failure, ensuring the valves stay open or closed in a disruptive power situation.
These compact VCAs measure just 0.75” in diameter and weigh only 2.3 ounces, yet can deliver a peak force of nearly two pounds in an operating stroke of ±2 mm with low hysteresis, zero cogging, high acceleration, and a long-life cycle.
Similar to the medical industry, equipment used in military and aerospace applications is dominated by a need to be as precise as possible in any environmental situation, so it has to be as rugged as it is accurate. In cases like these, custom solutions can help ensure that all the specifications to achieve desired performance are considered in the initial equipment design.
To address the unique requirements for a space-based application, Sensata engineers created a moving-magnet VCA that could handle the harsh requirements for a spectrometer moving mirror on the Origins-Spectral Interpretation Resource Identification Security Regolith Explorer (OSIRIS-Rex) spacecraft, which launched in September of 2016 to rendezvous with the Asteroid Bennu in 2018 and return samples to Earth in 2023.
This customized moving magnet VCA was attached to the moving-mirror assembly of the OSIRIS-Rex Thermal Emission Spectrometer (OTES) to properly position it to scan the surface as the spacecraft approached the asteroid. The custom VCA was specifically manufactured to ensure high reliability and fail-safe operation.?Redundant technology, low-outgassing, and high precision for exact motion control positioning were all key requirements to the actuator design.
Of course, given the extremely tight confines of a spacecraft, it was also critical to stay within the specific size, weight, and power limits, which were achieved in a compact housing measuring approximately 2” in diameter by 3” long. To meet the critical need for near-zero emissions, Sensata developed the actuator with as few adhesives or inks as possible and only spaceflight-approved materials, using mechanical assembly methods within a clean manufacturing process to eliminate substances that could cause outgassing.? In addition, high-energy Neodymium Iron Boron magnets were incorporated to provide superior operating efficiencies.
This custom magnet solution and clean assembly methodology was migrated into a range of actuators with varying sizes, resulting in high performance VCAs measuring 12?65 mm in diameter and 12?75 mm in length (at mid-stroke) that are ideal for semiconductor, military, space, and test and measurement applications.
The ability to put advanced precise linear motion anywhere is empowering both legacy application spaces as well as new uses not previously developed due to cost or complexity challenges. For example, a VCA built into an electric-vehicle charging system could raise and align the coil from the floor to the one in the bottom of the vehicle for optimum energy transfer, or on printer-head positioning in a high-resolution 3D printer.
The number of areas that can benefit from VCA technology are constantly expanding as engineers use VCAs to address complex, delicate, or sensitive motion applications. The key is to specify and develop the proper solution for the application, building on the strengths of the technology and the user’s needs.
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