Major depression is a serious medical disorder affecting more than 14
million American adults every year. Often a debilitating condition, depression
results in a persistent state of sadness which interferes with an individual's
thoughts, behavior, mood and physical health.
Common treatment for sufferers
involves pharmaceutical products prescribed by physicians that are sometimes
required for extended periods of time. Medications and professional counseling
will usually help patients manage the negative effects of depression but for
some, anti-depressants fail to provide improvement. Extreme cases can result in
complete incapacitation of the patient and hospitalization.
As an alternative to the
pharmaceutical approach to depression
treatment, Neuronetics Corp. of Malvern, PA, has designed the NeuroStar TMS
(transcranial magnetic stimulation) Therapy System. TMS is a non-invasive,
non-systemic treatment for depression that applies a highly focused, pulsed
magnetic field to stimulate function in targeted brain regions. NeuroStar TMS
Therapy is performed in a physician's office. Each treatment lasts about 40
minutes and takes place daily for four to six weeks. To date, NeuroStar reports
that there are have been none of the physical effects reported that are commonplace
with drug treatment. Patients can immediately return to normal daily
Click here for larger image.
A recent article in The Wall Street Journal titled, "Using Electricity, Magnets for
Mental Illness," detailed increasing research into techniques to stimulate or
calm the brain with electricity, magnets, ultrasound and infrared waves. The
article notes that "of the new brain-stimulation therapies, the most developed
is transcranial magnetic stimulation, (which was) cleared by the FDA in 2008."
Designing the TMS Device
NeuroStar engineers developing
the TMS treatment needed a reliable means of holding the treatment coil in
place during therapy sessions and turned to Ogura Industrial Corp. for
suggestions. This was a major design consideration as it is necessary for the magnetic
treatment coil to be able to be positioned in different axes of motion to
accommodate the different physical characteristics of individual patients.
convenience, depressing one button releases all the Ogura brakes, providing
freedom of movement to the system. The counter-balanced gantry can be extended
or retracted as well as rotated around the mast. The therapist manually moves
the coil into the most effective location. Once the treatment coil is
positioned and directed at the targeted brain region, the button is released
and the Ogura Power-Off Brakes lock and hold the coil in position for the
duration of the procedure. Should the position need to be readjusted, the
one-button operation provides for simple repositioning.
Once the patient is reclined in
the treatment chair, the treatment coil is positioned so that magnetic pulses
are focused on specific regions of the brain. It is critical that once the coil
is positioned and therapy commences, no slipping or wandering of focus location
occurs. The magnetic pulses generated by the treatment coil must remain on the
targeted area of the brain.
spring-applied brakes from Ogura were selected to hold the mast and gantry arm
of the TMS securely during the therapy sessions. These brakes, designed for
holding and emergency braking, are considered power-off brakes in that no power
is needed to hold the brake, due to the use of a spring to keep it in place. In
addition, the zero backlash feature of the RNB design eliminated the
possibility of flutter or drift of the gantry arm and mast during operation.
Furthermore, because the RNB is a
power-off brake, there is also no electrical signal to interfere with the TMS
system during use. Power is only applied to release the brake when the
treatment coil is adjusted to the individual patient.
Although it was not a primary
design consideration, cost of operation of the RNB is negligible. Power
consumption is minimized since the RNB is only energized while adjusting the
system to the individual patient. During treatment the RNB is static, stable,
non-interfering and power-free.
Spring Set Brake Details
The Ogura RNB-1.6Z Zero backlash
brake used in the TMS system is a self-contained electromagnetic system for
braking and holding rotary shafts with high angular accuracy.
Power off (or spring set) brakes
use coil springs to apply a force to stationary plates to squeeze or clamp a
rotating disc. When the rotating disc needs to spin freely again, a dc
electromagnetic field is used to act against the spring forces, releasing the
Most spring set brakes contain a
bit of radial air gap or looseness between the rotating disc and the customers
shaft. This is called backlash, and in most applications is not an issue.
However, in exact positioning applications, like Neuronetics TMS, backlash is
detrimental to system performance. To eliminate backlash and make the brakes
suitable for Neuronetics' positioning requirements, Ogura designed a unique
For Neuronetics' TMS, Ogura used
a machined steel drive hub (affixed to the customer's shaft using a key and two
sets screws). This drive hub is fixed to Ogura's low inertia flat spring steel
friction disc. The resulting strong, yet flexible disc allows for stiff (zero
backlash) radial torque while smoothly flexing (axially) during braking.
Ogura's high coefficient friction
material is bonded to the brakes pressure plate and backing plate, both of
which will make contact with the rotating steel friction disc during braking.
On most zero backlash brakes the friction material is bonded to the steel disc,
which means the friction material would rotate during disengagement. Since
Ogura bonds the friction material to the non-rotating components, only the thin
spring steel disc rotates so higher operating speeds can be achieved. More
importantly, there is less vibration because the thin steel disc is inherently
balanced. To ensure smooth braking and high torque, the pressure plate/friction
disc and the backing plate/friction disc assemblies are precision ground for
flatness before assembly.
Constant torque is created by the
use of three coil springs captured in precision trepanned cavities. These
springs apply even pressure to the pressure plate to contact and compress the
friction disc against the stationary backing plate.
brake is engaged (and shaft stopped) the Ogura spring steel friction disc
assembly holds the load firmly and will not flex radially. This provides a firm
position for the equipment to apply the proper magnetic pulses to the patient.
To release the brake, a dc
voltage is applied to the coil, creating a magnetic field in opposition to (and
stronger than) the springs clamping forces. This attracts (pulls) the pressure
plate back though its air gap, releasing the brake from the friction disc/drive
hub assembly and allows the shaft to turn freely with no drag or noise.
This was an important
consideration in the TMS design, since quiet operation is essential in a
therapeutic environment. Since the RNB power-off brakes are only energized when
the treatment coil is being positioned, the treatment coil, once put into
place, is held securely with no electrical noise or "hum" to distract the
Another feature of the RNB-Z
series brake is that, because of its unique hub arrangement, it can operate in
any orientation (shaft verticle for example) and not produce any residual drag
when the brake is disengaged. A traditional splined hub design would have
produced both unwanted drag and noise in Neuronetics' sensitive application.
Frank Flemming is president of Ogura Industrial
for more information.