Abourachid, A.

Böhmer, C

Chablat, D.

Chevallereau, C.

Fasquelle, Benjamin

Furet, Matthieu

Wenger, Philippe

English

Archive Ouverte en Sciences de l'Information et de la Communication

HAL Id: hal-02265058
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Submitted on 8 Aug 2019
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Combining precision and power to maximize
performance: a case study of the woodpecker’s neck
C Böhmer, A. Abourachid, Philippe Wenger, Benjamin Fasquelle, Matthieu
Furet, D. Chablat, C. Chevallereau
To cite this version:
C Böhmer, A. Abourachid, Philippe Wenger, Benjamin Fasquelle, Matthieu Furet, et al.. Combining
precision and power to maximize performance: a case study of the woodpecker’s neck. 44ème congrès
de la Société de Biomécanique, Oct 2019, Poitiers, France. ￿hal-02265058￿
 Combining precision and power to maximize performance: a case study of the 
woodpecker’s neck 
 
C. Böhmera*, M. Furetb, B. Fasquelleb, P. Wengerb, D. Chablatb, C. Chevallereaub and A. Abourachida 
aUMR 7179 CNRS/MNHN, Département Adaptations du Vivant, Muséum National d’Histoire Naturelle, 55 rue Buffon, 
75005 Paris, France; b Laboratoire des Sciences du Numérique de Nantes (LS2N), CNRS, Ecole centrale de Nantes, 
44321 Nantes, France 
 
Keywords: neck; bird; tensegrity; bio-inspired, robotics 
 
1. Introduction 
The neck in birds has been characterized as a highly 
complex system that positions the head during all kinds 
of behavior (Böhmer et al. 2018; Zweers et al. 1994). 
This involves a variety of highly demanding tasks such 
as feeding, manipulation, preening, sexual display, 
nest building, and combat behavior (Böhmer et al. 
2019). This versatility is an opportunity for 
bioengineering, but prior to designing a technological 
model, the biological system must be understood; in 
particular regarding the form-function relationships. 
One behavioral pattern in birds that appears to be 
relatively constrained is pecking in woodpeckers. 
There is evidence that the drilling trajectory is 
essentially planar (Spring 1965). From a 
morphofunctional point of view, woodpeckers are 
highly interesting because they are very lightweight 
(mean body mass = 300 g), but are capable to dig into 
dense tree trunks (Puverel et al. 2019). They strike their 
beak against a tree repeatedly with high accelerations, 
high velocity and large force transmissions (May et al. 
1979; Wang et al. 2011). We took this bird species as 
a first example for a biologically inspired robot arm 
that combines precision and power to maximize 
performance. 
Adding biological knowledge into the design process 
requires a simplification of the complexity of the 
biological entity (Whitesides 2015). In this context, we 
(1) analyzed the neck musculature which supplies 
force for movement; (2) established a planar robotic 
model using several stacked tensegrity crossed bar 
mechanisms and (3) integrated all data into an actuated 
model of the bird neck. 
 
2. Methods 
2.1 Dissection 
The neck musculature of one generalist bird (Corvus 
monedula) and three species of woodpeckers was 
comparatively investigated by quantitative dissection: 
the green woodpecker (Picus viridis), the great spotted 
woodpecker (Dendrocopos major) and the black 
woodpecker (Dryocopus martius). They differ in 
pecking performance (Jenni 1981) which allows 
identification of muscular adaptations specific for high 
power. After removing the skin and fascia, each 
muscle was identified and systematically detached 
from both the origin and insertion. Muscles were 
assigned to main functional categories indicating the 
direction and vertebral region of action. The 
craniocervical muscular system was illustrated in a 
schematic diagram. 
 
2.2 Kinematic and dynamic modelling 
The woodpecker neck is modelled in the sagittal plane 
with a serial stack of Snelson’s X-shape tensegrity 
mechanisms (Wenger & Chablat 2017), which is a 
class 2 tensegrity mechanism composed of an 
antiparallelogram made of 4 rigid links. The sides of 
the mechanism are attached with two springs that 
ensure a stable rest position, and cables run through the 
springs. By modifying the cable tension with motors, 
different positions can be reached. The kinematic 
model links the output of the modelled stacked 
modules (i.e., the position and orientation of the tip of 
the beak) to the input of the robot (the orientation of 
each X-shape mechanism). The dynamic modelling 
takes into account the influence of the rigid links 
masses and inertia, spring stiffnesses and cable 
tensions and links the motion of the model (position, 
velocity, acceleration) to the forces needed to move it 
(Furet et al. 2018). 
 
3. Results and discussion 
3.1 Muscular adaptations 
The overall muscular system of the neck in the 
analyzed woodpeckers corresponds to an earlier 
anatomical description of Dendrocopus provided by 
Jenni (1981). Our quantitative analysis revealed that 
the adaptation to pecking is particularly evident in the 
craniocervical and ventral muscle system. 
As opposed to generalist birds, the muscles of the 
craniocervical system in woodpeckers show 
adaptations specific for precision of force control. The 
highly specialized tendinous architecture of the ventral 
muscle system in woodpeckers enables forceful and 
rapid movements. Compared to the other species of 
woodpeckers, the tendons are most prominently 
developed in the black woodpecker. 
In summary, the anatomical arrangement of muscle 
and tendon in the neck of woodpeckers facilitates 
efficient pecking by combining precision and power. 
 
3.2 Neck movement 
Videos of alive woodpeckers do not allow us to 
precisely detect the neck movement because of the 
feathers. As a consequence, a film of the corpse of a 
green woodpecker without its feathers and moved by 
hand was recorded and used to capture a neck 
movement, with the aim of reproducing it with our 
robot in simulation. 
To convert the video into a robot movement, the 
frames are analyzed independently. For each of them, 
the middle line of the neck is detected, then the 
mechanisms of the robots are placed one by one from 
the bottom of the neck. The obtained positions give us 
the trajectory. 
 
3.3 Simulation 
The manipulator is made of 11 identical mechanisms 
that is the number of vertebrae in the green 
woodpecker. The dimensions were chosen to have a 
manipulator with the same proportions than the 
woodpecker neck. 
Simulations are performed with Matlab Simulink and 
Simscape Multibody. The use of the dynamic model in 
the control law allows obtaining an accurate tracking 
with a full-actuated robot. In this case, the forces 
applied have similar shapes for each mechanism, 
which is promising for under-actuation. 
Simple under-actuation strategies also succeed at 
tracking the movement with a good precision, and the 
neck musculature of the woodpeckers will be used to 
create related under-actuation strategies. 
 
4. Conclusions 
The aim of the present work was to extract the 
anatomical parameters that are essential to perform 
precise and powerful movements. The 
conceptualization of the extremely complex 
musculature of the neck in birds revealed such a 
specialization. Eventually, the prototype of the 
woodpecker’s neck will serve as a starting point for 
future invention and application such as industrial soft-
robots that execute their task in collaboration with 
humans in an efficient and safe way. 
 
Acknowledgements 
We thank the Chene Association and the Goupil 
Association for providing bird specimens for 
dissection. This study was financially supported by 
the Agence National de la Recherche (ANR): Project 
ID #ANR-16-CE33-0025 (AVINECK), Project 
coordinator: A. Abourachid. 
 
References 
 
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relationships between skeletal dimensions and 
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length in birds. R Soc Open Sci 6: 181588. 
Furet M, Van Riesen A, Chevallereau C, Wenger P. 
2018. Optimal design of tensegrity mechanisms 
used in a bird neck model. European Conference on 
Mechanism Science. 365-375. 
Jenni L. 1981. Das Skelettmuskelsystem des Halses 
von Buntspecht und Mittelspecht Dendrocopos 
major und medius. J Ornithol 122: 37-63. 
May PR, Fuster JM, Haber J, Hirschman A. 1979. 
Woodpecker drilling behavior. An endorsement of 
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Puverel C, Abourachid A, Böhmer C, Leban J-M, 
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*Corresponding author. Email: boehmer@vertevo.de 
 


Combining precision and power to maximize performance: a case study of the woodpecker's neck

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Combining precision and power to maximize performance: a case study of the woodpecker's neck

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