Designing Whisker Sensors for Noisy Environments
Teresa A. Kent, Suhan Kim, Mahnoush Babaei, Hannah Emnett, Mitra J. Z. Hartmann, Sarah Bergbreiter

Abstract—Whiskers are a sensing method that could allow
robots to obtain detailed tactile information about an environment with minimal damage risk. When a whisker contacts anobject, it bends, transmitting mechanical signals to its base.
Because whiskers are proximal sensors and do not depend on
light, they succeed when vision-based sensors are most likely tofail. However, the benefits of whisker sensors are still limited
to laboratory environments, partly because separating usefulfrom noisy sensor signals is much harder in the unstructured
world. Here we present two versions of whisker sensors thatbegin to address this challenge. The first sensor can remove
airflow and inertial effects from contact signals. This sensor isalso highly reconfigurable, making it an accessible testbed toinvestigate differing whisker array geometries. The second sensor
can determine whether the whisker makes contact with a rigid
versus a compliant surface. As tactile information from engineered whisker sensors becomes more informative and reliable,
robotic platforms can make more informed choices about theirinteraction with the world.

Fig. 1. A diagram of the WhiskSight sensor. Whiskers (rigid carbon fiberrods) are attached to an elastomer membrane suspended above a camera. The
attachment uses disc magnets above and below the elastomer membrane forattachment, so the whiskers are easy to reconfigure. B) The camera captures
the motion of the bottom of the magnet and uses it to calculate the whiskers’
magnitude and direction of rotation, ϕ and θ in spherical coordinates. Thewhiskers are rigid so there is no bending, only rotation C) During rotation,
only the bottom of the magnet moves. The arrows show motion of a tracked
point in the camera image at 10x scale. This figure is reproduced from [4]Tactile exploration of unstructured environments presents
multiple challenges. Tactile sensors require a large dynamic
range, as they must contact objects with varying forces andspeeds. They must remain sensitive to small and robust tolarge contact forces while avoiding breakage and damage.
Moreover, it is not just the sensor that risks breakage; damage
to the environment is of equal concern—grasping, moving,and contacting objects all present opportunities for accidental
damage. Finally, because tactile sensors are proximal, ensuring
a 3D space is adequately covered is an additional challenge.
Whisker-based sensing represents an approach towards tactile sensing with the potential to meet these challenges. Mirroring their biological counterparts [7], engineered whisker sensors keep their transduction method at or below the whisker’sbase [2, 5, 6, 1, 8, 9]. This geometry allows sensing electronics
to be separated from the regions of the sensor that directlyinteract with objects, an approach that has also sometimes beenused for tactile skin sensors [1, 10, 11]. The separation protects
the electronics and allows the interactive portion of the sensor
to be soft and compliant, minimizing damage to both sensor
and environment. More specifically, many engineered whiskers
are designed to bend during contact [2, 8]. The complianceallows whisking to occur at high speeds with minimal concernthat unpredicted contact will exert large forces on the environment or the sensor. Engineered whisker sensors may also
provide a safe and efficient means to map unknown 3D spaces.
The whiskers’ extended lengths can speed up the process oflocating contact versus noncontact points in a 3D environment.
This extended coverage is enhanced further when the whiskers
are rotated, or “whisked,” through space.
In laboratory environments, whisker sensors can gather
high-density shape information [6, 9], map 3D spaces [2, 8],
and classify objects [5]. However, achieving these feats in

unstructured environments with multiple objects, non-contact
stimulus sources, and moving/compliant objects is still challenging. The present work describes two whisker sensors designs that begin overcoming these challenges. The first sensor,
WhiskSight [4], uses magnets to attach six rigid whiskers
to create an easily-reconfigurable testing platform, ideal forinvestigating how whisker placement affects the informationacquired (Fig. 1A). We show that this sensor can detect signals
caused by airflow and by self-motion (inertia). These signals
sometimes confound contact sensing of external objects, butsince WhiskSight can detect them, they can be removed. The
second design combines a tapered, flexible whisker with aspring suspension system. Because the whisker is both tapered
and flexible (Fig 2A), we can differentiate between whisker
contact with a compliant and a non-compliant surface.
The rat whisker array consists of rows and columns of
30 whiskers with different lengths, curvatures, and thicknesses [7]. Whisking motions allow rats to detect, locate, andidentify objects even in total darkness. However, few if any
studies have quantified the relative effectiveness of different
configurations of heterogeneous whiskers in an array for
robotic applications. Although testing many different whisker
arrangements may provide insight, rearranging the sensors canbe time consuming and annoying, as both power and signal
wires must be managed. Rearrangement of robotic whiskers
typically increases the likelihood that the system will break.
By combining the camera transduction method shownin other sensors [11, 10, 6] with magnetically detachable
whiskers, the WhiskSight sensor facilitates studies into theeffect of array shapes on information gain [4]. The camera images from beneath the whisker array, and each of the whiskers

to sense quickly in predictable environments while slowing
down when the sensed signals are more ambiguous.
The two sensors represent engineered whiskers that canovercome some of the challenges from uncertain environments: information gain, robustness and opportunities for error.
With continued improvements in engineered whisker sensors,
the robots that employ these sensors can make informed
decisions about their interactions with their environment.
R EFERENCES

Fig. 2. A schematic of the compliant whisker sensor: A) A 3-d contact point
on a whisker has three components: contact direction, contact magnitude, andthe radial distance of contact. When laser cut springs suspend a compliant
whisker, contact forces cause both rotation and translation at the whisker’sbase. By tracking nine points on the suspension system, we can determine
the rotation and z-translation of the whisker base. B) Pure z-translation (axialforce) brings the nine tracked points closer to the camera, increasing theirapparent size. C) Pure rotation most strongly affects the black tracked dot in
the image center. The arrows represent 10x the motion of the point in pixels.

is marked red to permit easy identification and tracking.
Researchers can change the array shape, and a segmentation
algorithm automatically determines the new shape (Fig 1C).
Once the array shape is determined, the magnets’ rotationand elastomer’s motion are tracked using python’s OpenCV
package. This method yields rotation magnitudes accurate to0.5◦ and rotation direction direction accurate to 6.5◦ (Fig 1B).
Finally, each whisker’s response to contact is distinct from its
response to airflow or inertial stimuli, allowing signals fromcontact and non-contact stimuli to be differentiated.
The second version of the whisker sensor switches theelastomer suspension of WhiskSight for a spring suspension
with a signal maximizing design. This enables the ability
to detect downward deflections caused by axial forces anddetermine the point of contact along the whisker length (Fig2A). In this design, four (red) points above the spring andfive (4 blue, 1 black) points below the spring are tracked(arrows, Fig 2B,C). Unsurprisingly, when sensors can localize
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