SUCCESS STORY – No Compromises Allowed For Mobile Drug Pumps-- Gernot Hamann --No Compromises Allowed For Mobile Drug Pumps
Piezo-Based Ultrasonic Drives Open Up New Opportunities

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

Page 1 of 4

SUCCESS STORY – No Compromises Allowed For Mobile Drug Pumps-- Gernot Hamann --For many diseases, mobile drug pumps are indispensable tooutpatient therapy, for instance, in pain therapy, oncology,
parenteral nutrition as well as metabolic disorders. They
enable patients to be mobile, therefore contributing to their
quality of life. At the same time, therapy costs are reduced, as
the patients do not require in-patient or out-patient
treatments at the hospital.
There is, however, room for improvement in the standard
mobile drug pumps used today, especially when it comes toflexibility with regard to various applications, size, weight andreliability. In this regard, piezo ultrasonic motors as pumpdrives can open up interesting opportunities (Fig. 1).

Depending on therapy, such flexibility enables drugs to beadministered in larger or smaller quantities. It is even possible
not to administer any drugs for extended periods of time.
Large-volume dosing is also possible, as drug reservoirs withvarying capacities can be attached to the pumps. The
peristaltic pumps are suitable for various medications, as they
deliver a continuous flow (basal rate), but even special
injections (bolus rates) are also easy to dose and can bescheduled in any manner. In addition, all procedures can bedocumented to evaluate specified drug quantities and thecourse of therapy and to submit relevant data to insurance
providers.

Utilizing Potential for
Improvement: Mobility andDocumentation
This finally boils down to the fact that except for mobility,
peristaltic pumps combine all desired requirements. Hence,
their dimensions should be as small as possible, they should
be light and silent, limiting the user in their mobility as little
as possible. Equally important are low energy consumption
for a long battery life and reliable low-wear operation for long
maintenance intervals. In this context, it is worth examining
the drives that are typically used in the peristaltic pumps:
Fig. 1

For many diseases, mobile drug pumps are indispensable tooutpatient therapy, for instance, in pain therapy. There is room
for improvement, however, especially when it comes toflexibility with regard to various applications, size, weight andreliability (Image: PI)

When thinking of mobile drug pumps, balloon pumps arewhat first comes to mind, as they are light, can be easily
handled and operated by patients. But they show significantdeviations in regard to the rate at which the medication isdispensed and the injection quantities are difficult todocument.
Since the "mobile" patient is usually not in the hospital, it isextremely important to precisely monitor the course oftherapy. The physician needs accurate information for a
successful treatment. Therefore, a pump system is required
which also allows for exact documentation outside thehospital. For such cases, peristaltic pumps are currently thebest solution. But due to their considerable weight and size,these pumps severely restrict the patients and are thus notreally mobile. They do, however, allow for a precise dosage
and programmable volume flows.

Although the small gear-based electric motors that are often
selected generate the necessary high power or torques
required for pumping, they are also slow; their mechanicalmicro-gears are seldom free of backlash and are furthermore
very vulnerable to wear. Therefore, this solution cannot be
considered to be truly reliable, because short maintenanceintervals involve effort and costs.
There are also disadvantages associated with using direct,
gearless drives. Depending on the design of the peristaltic
pumps, comparatively less power or torque is delivered.
Therefore, a larger drive must be selected, which in turn canaffect the pump dimensions. In addition, the direct drives
may respond faster but are not self-locking because the gearsystem is absent. To retain a stable position when at rest,
they must consequently be supplied with current. For short
operating cycles, i.e. if the duration of the medication is shortand the rest periods are long, this has a severe impact on thebattery life. The motor must therefore be mechanically
blocked, even if it involves considerable effort.
All of the above are therefore ample reasons to search for analternative drive solution for mobile drug pumps.

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

Page 2 of 4

SUCCESS STORY – No Compromises Allowed For Mobile Drug Pumps-- Gernot Hamann --Compact Drive for Mobile Use
Piezo-based ultrasonic drives can open up new opportunities
here. They are very compact, low-wear and self-locking. They
therefore maintain their position not only when powered off,
but also if they are dropped or hit. Due to their operating
principle, their low profile and their individual adjustment
options, they can be easily integrated into mobile drug pumps(Fig. 2) and work almost noiseless.

Fig. 3

Oscillations with ultrasonic frequencies of a piezoceramic
actuator are converted along a friction bar in a linear motion andthereby drive the movable part of a mechanical structure(Image: PI)

Various Designs are Feasible
The drives are built in a very compact manner, as they consist
only of the piezo actuator and an embedded movable disk orlinear axis. The drive electronics can be integrated as a chipand requires very little installation space (Fig. 4).
Fig. 2

Due to their operating principle, their flat design and theirindividual adjustment options, the piezo-based ultrasonic drives
can be easily integrated into mobile drug pumps (Image: PI)

It is easy to understand how these compact piezo drives work(Fig. 3):
Oscillations with ultrasonic frequencies of a piezoceramic
actuator are converted along a moving runner in a linear
motion and thereby drive the movable part of a mechanicalstructure. The core piece of the drive is a monolithic piezo
ceramic (stator), which is segmented on one side by twoelectrodes. Either the left or right electrode is excited to thehigh-frequency natural oscillations of the piezoceramicelement in the range of several hundred kilohertz andthereby determining the direction of motion.
A coupling element attached to the piezo ceramic is thus
induced to fast linear motion. In contact with the runner,
micro impulses move the movable part of the mechanicalsystem (sled, rotary plate etc.) forward or backward. Eachoscillation cycle moves the mechanical system by a few
nanometers, thus producing an even motion with atheoretically unlimited travel range.

Fig. 4

Flat and small dimensions due to hollow runner design(Image: PI)

In addition, the solution is extremely low-wear and reliable,
as there are few mechanical components such as gears.
Dosages are possible in a wide range of speed spectrum.
Depending on the design, dosages can be made from a few
degrees up to several rotations per second, or, in the case of
linear solutions, they can be made from less than 1 mm persecond up to several 100 mm per second. Position feedback
for the control is available for precise documentation.

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

Page 3 of 4

SUCCESS STORY – No Compromises Allowed For Mobile Drug Pumps-- Gernot Hamann --Image 5 shows how such a mobile drug pump can be built:
The motor consists of a piezoelectric ring (actuator). Thisactuator is excited in such a manner that a so-called travellingwave is generated. The thin aluminum oxide rings fitted onto
the piezo ring (top and bottom) absorb the oscillations.
With the help of the three coupling elements used in therotor, the absorbed oscillations are transmitted to the preloaded rotor and converted to a rotary motion. The piezo
ultrasonic drives, which are arranged in a circular form, movethe disk. It is built in such a way that thanks to the special
geometry, different drug quantities can be dosed.

Fig. 6The PILine® motor can also be arranged on the side (Image: PI)

About PI
In the past four decades, PI (Physik Instrumente) with
headquarters in Karlsruhe, Germany has become the leading
manufacturer of nanopositioning systems with accuracies in
the nanometer range. With four company sites in Germany
and fifteen sales and service offices abroad, the privately
managed company operates globally.
Over 850 highly qualified employees around the world enable
the PI Group to meet almost any requirement in the field ofinnovative precision positioning technology. All key
technologies are developed in-house. This allows thecompany to control every step of the process, from design
right down to shipment: precision mechanics and electronics
as well as position sensors.
The required piezoceramic elements are manufactured by its
subsidiary PI Ceramic in Lederhose, Germany, one of the
global leaders for piezo actuator and sensor products.

Fig. 5

A compact piezoelectric ultrasonic motor moves the disk. Thissystem is built in such a way that thanks to the special geometry,different drug quantities can be dosed (Image: PI)

Other designs are feasible with piezo ultrasonic drives, too.
The piezo actuator can, for instance, also be arranged on theside (image 6) and it can rotate a ring. In the large aperture ofthis ring other components can be arranged. Drug pumps
built in such a manner are particularly small, light and silent.
In addition, they offer a high degree of flexibility with regard
to various therapies and dosages. In future, even morepatients can thus benefit from an outpatient or ambulatory
therapy.

PI miCos GmbH in Eschbach near Freiburg, Germany, is aspecialist for positioning systems for ultrahigh vacuum
applications as well as parallel-kinematic positioning systems
with six degrees of freedom and custom-made designs.

Author

Dipl.-Physiker Gernot Hamann, Head of Key AccountManagement at PI (Physik Instrumente)

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

Page 4 of 4