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Ideas in motion – integrating motors and motion control components

The growing momentum behind the move towards personalised medical devices presents many challenges for medical device designers, not least the integration of motors and motion control components. Herbert Trummer of Sonceboz tells Medical Device Developments how this trend and other drivers of innovation are changing the design of motors.

At the core of many new medical devices lies a motor or motion control component that determines how well the device performs its function. Driving the development of these essential components requires manufacturers to keep pace with the emerging trends in healthcare, which today means understanding the implications of personalised medicine and the push toward home care for outpatients who might once have stayed in hospital for extended periods.

Medical device designers will always want higher efficiency, more speed and increased power from smaller, more robust and quieter motors, but for each device these priorities will differ. The onus, therefore, is on designer and manufacturer to ensure that motors precisely meet the needs of new devices, whether in the hospital or for portable use at home.

Personalised medicine (PM) has implications for both the pharmaceutical and the medical device industries. It is about achieving a more precise diagnosis of a disease, taking into consideration the specific situation of the patient, and from there designing an individual treatment that will produce better patient outcomes. It is firmly based on a process of obtaining individual data from the patient, and the development of specific, appropriate drugs and unique treatment plans. While this might not immediately seem to have a direct effect on medical devices, the PM trend is part of a broader move to push patient care out of the hospital and into the home whenever that is a safe and effective option.

Herbert Trummer, director of the mechatronic division at Sonceboz, which specialises in the development and production of mechatronic drive systems for medical devices, says that while his company has yet to be "confronted with special requirements for motors and drives that derive directly from the specific requirements of personalised medicine", he recognises that "the trend toward individualisation in healthcare is here, and can also be found in the increasing demand for portable devices".

"Patients are leaving hospital earlier than in the past," he continues. "The average length of stay of a patient in the hospital is decreasing and more treatments are typically carried out at home, without the support of medically trained people. Thus, there are some generic challenges for such portable home devices, such as ease of use."

As well as portable and hospital devices, Sonceboz’s components are also found in laboratory and diagnostics systems.

"Dialysis is an important area, for example, as well as the dosing of heparin," says Trummer. "For dialysis machines we provide noiseless pumps to push the blood, and that is a market where machines are produced in high volume each year. Reducing the amount of noise made by motors is also a high priority when it comes to portable devices, but there are many other considerations."

Challenge defines the solution

When designing an electric motor or mechatronic drive system to be suitable for portable and home care devices there is great emphasis on low electrical consumption, extended life, compact profile and low weight. Designers want low-maintenance components adapted for battery-operated devices, low cost, low complexity and fast time-to-market, and while most devices will perform better if motors meet these requirements – and others, such as being more robust and quieter – the emphasis designers put on each of these characteristics will vary between devices.

"More battery-powered portable devices are used in patient homes, but there is no single appropriate motor for such devices," says Trummer. "The requirements of the motor depend very much on the design of a specific device. Nevertheless, miniaturisation and efficiency will always be important features. For autonomy, the lifetime of the battery needs to be longer."

He adds: "Every application has its specific requirements and needs a specific solution."

Understanding the key features of motor design therefore requires an in-depth investigation of the performance parameters of the device for which the motors are intended.

"Collaboration with an acknowledged specialist in mechatronic systems can often help to reduce development time and time-to-market."

"Everything depends on the application," believes Trummer. "For blood pumps, the key element is lifetime reliability and a reduction in noise output. In other applications, miniaturisation might be more important, or perhaps the priority will be the shape of the motor to fit the device. Miniaturisation is a very important trend right now, as is the flat form factor of the motor and quieter performance."

However, for portable medical devices with motors and motion control systems it is vital to prioritise comfort and ease of use, which is often determined by the degree of miniaturisation, or the noise level of motors and gears, and yet motors are moving parts and are subject to wear, so miniaturisation cannot be achieved at the expense of reliability.

"For the incorporation of mechatronic drives into medical devices, Sonceboz uses motor technologies that are precisely developed, and then produced in very high volumes on fully automated assembly lines," explains Trummer. "Reliability… [is] a direct result of this process."

The company has invested in the development of a driver technology called LoadSense, which it says "allows highly efficient control of the motor current, and at very low noise levels". The technology leads to improvements in the use of battery power because it comprises a brushless permanent magnet motor controlled by an electronics system that allows the measuring of the load angle of the motor. This information is used to determine not only the position, but also the load of the motor at any time, which Sonceboz says allows more precise control of the motor with less power consumption. Due to using a high number of pairs of poles, the result is a motor with high torque at relatively low speeds.

The adaptation of such technologies to suit specific medical devices is often only possible when device designer and component supplier undertake a thorough process of integration. With portable devices, this shared approach to integration becomes more important because the goal is to position motors and control systems effectively within a very small space.

"When it comes to balancing miniaturisation with improved efficiency there are two aspects to consider," says Trummer. "On one hand, component motors that are smaller and have higher efficiency are better for the designer of a medical device, but on the other hand they must consider the integration of the complete device. The designer may choose an off-the-shelf motor, but connecting it adds both cost and complexity, which drives down cost-efficiency.

"The degree to which cost-efficiency suffers depends on the scale of production. Producing devices on a larger scale will drive down costs, but those gains will be improved by integrating the motor into the device at an earlier stage in its design," he adds.

A shared process

Fully integrated motor systems have clear advantages over the use of off-the-shelf components in terms of ease of use, performance and reliability, although there could potentially be increases in cost if the devices are manufactured in small numbers. For larger production runs, however, integration is highly cost-efficient, but it requires coordination of efforts by device designers and manufacturers of components.

"Designers are increasingly aware of the importance of integration, so they are more willing to work with companies like ours in the design process," says Trummer. "We always look at real integration rather than delivering motors that have been selected from a catalogue of standard products. We look at problems with our customers and solve them through a process of optimisation, although this approach does require our customers to produce a high volume of devices."

If the production processes are automated – as is increasingly the case – the problems of using standardised components are compounded.

"The possibility of automating the production of medical devices is strongly linked to the designs of the different components," explains Trummer. "A good example of this idea is the previously mentioned standard motors. In most cases, the connection is made by open leads or perhaps an integrated cable connector – with that, an automated assembly of the motor into the device is very difficult."

It is clear, then, that there is no single solution to the varied demands of portable device manufacturers, and that almost every device requires its own approach with regards to any decision about motors. The key, therefore, is to consider the requirements of the motor at an earlier stage in the design process, possibly in partnership with the component manufacturer.

"We don’t think there is a single match for all solutions," says Trummer. "What we propose is to carefully analyse the specific requirements and the business case, and then to formulate a solution based on standard products, with an integrated mechatronic drive solution. [This] way may require perhaps a little more investment in R&D, but there will surely be a greater return in terms of the cost, reliability and miniaturisation of the device, as well as the possibility of automating the assembly process.

"Additionally, collaboration with an acknowledged specialist in mechatronic systems can often help to reduce development time and time-to-market."

Partnering with component suppliers to create bespoke solutions also allows device designers to benefit from the innovation that is inspired by the highly competitive environment in which those suppliers work, as well as helping component manufacturers to keep pace with the demands of an evolving healthcare sector and with the growing potential of the technology behind medical devices.