How the TRACKER™ position sensor improves camera designs
- Faster, more precise focus and/or zoom. The TRACKER
enables high-resolution direct linear closed-loop control. With
better resolution than open-loop systems or optical encoders,
the lens moves more quickly to a more exact position.
- Less waiting to take a picture. The TRACKER provides
absolute position information over a 2 mm distance. This means
that there is no need to reinitialize to reestablish a zero
reference on power up. There is less waiting for the camera to
be focused and ready.
- Lower power use saves batteries. Faster ready time
means less power is used on power up. The TRACKER also uses less
power to maintain position, and can be powered off completely in
standby mode.
- Enables smaller cameras. With the TRACKER you can
eliminate the external zero reference sensor. And because it
enables more precise focus, you can achieve superior results
with smaller optics.
Figure 1:
Miniature TRACKER position sensors fit into existing space to reduce
power use and improve precision of focus and zoom. This unique
sensor offers smallest size, unlimited travel, and 0.5
μm
resolution.
What is the TRACKER™ position sensor?
The TRACKER position sensor is a magnetic sensor array with 0.5
μm resolution and integrated on-chip digital encoding. Less than 1.5
mm thick and 3.9 x 2.5 mm (in chip-scale packaging), it fits in the
smallest digital cameras. It delivers absolute positioning in a 2 mm
range. Unlike optical encoders or stepper motors, it does not
require a separate zero-reference sensor.
 To
use the TRACKER in an optical system, a magnetic strip with
alternate north-south poles is mounted on the moving optics mount
and positioned above the sensor (Figure 2). The magnet should have
pole length of 1 mm and pole pair length of 2 mm. A half pole is
required at each end of the strip. The length of the strip
determines the maximum measured stroke.
The TRACKER has a Hall sensor array on the chip. This array
measures the spatially-varying magnetic field produced by the moving
magnetic strip. An integrated digital encoder on the chip provides
direct digital output of the absolute linear position within a 2 mm
pole pair on the magnet. By counting pole pair crossings, a system
processor can determine absolute position along the length of the
magnet.
The absolute magnitude of the magnetic field intensity is used to
detect the end of the magnetic strip and serves as a built-in zero
reference. Standard I2C protocol enables simple integration into the
system processor.
Advantages over open-loop stepper motor designs
In a stepper motor system, a known position is reached by moving
a set number of steps from the reference sensor. Each direction
change requires a position offset to correct for backlash –
typically about 10 µm (Figure 3a). Backlash can change over time,
making the factory offset inexact and limiting precision of focus or
zoom. The TRACKER, on the other hand, provides actual position
information with a resolution of 0.5 μm and bi-directional
repeatability of better than 2 μm. Focus is faster and more precise
(Figure 3b).
 
Consider replacing the stepper motor and lead
screw mechanism with a miniature piezo SQUIGGLE® motor for even
greater precision, smaller size and lower power use.
Another drawback to open-loop stepper motor systems is that the
position information is lost on power down: The motor must return to
the zero reference sensor upon power up and then re-focus. This
means a longer ready time and more power use. In contrast, the
TRACKER’s built-in zero reference provides rapid absolute position
reading on power up. (User-provided flash memory stores the pole
count information on power-down.) This allows you to power off the
system or put it into sleep mode to conserve power – the sensor
returns absolute position on power-up without the need to
reinitialize, for nearly instant ready time with less power use.
Advantages over optical sensors
The TRACKER position sensor offers distinct advantages over
miniature optical encoders in digital cameras. Because it is a
magnetic sensor, it does not require a light source – eliminating
that potential source of image degradation.
The TRACKER offers four times better resolution for more precise
focus and zoom. In addition to giving your users better performance,
this higher precision can allow you to use smaller optics, further
reducing your system size.
The TRACKER uses less than one tenth the operating power of
optical encoders when the lens is being moved. Furthermore, the
TRACKER can be powered off when the lens is not moving, reducing
power use even more. This can have a significant impact on camera
battery life.
Optical encoders are incremental encoders and must hunt for a
zero position on power-up. As described in the previous section,
this results in a longer wait before the camera is ready to take a
picture, and also in increased power use. The TRACKER is an absolute
encoder and returns position information immediately on power up for
faster focus.
The TRACKER is much smaller than optical encoder solutions.
Optical encoders require a separate zero-reference sensor, with the
encoder and reference sensor taking up about twice the volume of the
TRACKER with its built-in zero reference.
Packaging
The
TRACKER NSE-5310 is available in custom wafer-level chip scale
packaging as small as 3.9 x 2.5 x 0.6 mm and in chip-on-board
packaging measuring 5.4 x 4.2 x 0.6 mm (Figure 4).
New Scale offers
evaluation kits
for easy handling during
evaluation and system development. In this kit, the TRACKER NSE-5310
is packaged in a TSSOP 20 and mounted on a PCB with flex cable
(Figure 5). The kit includes a suitable linear magnetic strip, along
with an MC-31MB interface card and New Scale Pathway™ software with
intuitive user interface to facilitate evaluation.
For more information
- Please refer to our TRACKER
overview page for additional specifications, data sheets and
ordering information
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The TRACKER™ NSE-5310 miniature position sensor allows
designers to quickly and easily improve autofocus and zoom
mechanisms in existing digital still camera, video camera and
similar product designs. Use this sensor to: