# Mechanical performances of DREEVEN, a novel motorization unit for custom knee orthosis

L Colas, K Giraud-Esclasse, R Temporelli

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L Colas, K Giraud-Esclasse, R Temporelli. Mechanical performances of DREEVEN, a novel motorization unit for custom knee orthosis. 48eme Congrès annuel de la Société de Biomécanique, Oct 2023, Grenoble, France. hal-04227858

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Submitted on 4 Oct 2023

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# Mechanical performances of DREEVEN, a novel motorization unit for custom knee orthosis

L. Colas, K. Giraud-Esclasse, R.Temporelli

REEV SAS, Toulouse, France

## 1. Introduction

In Europe and the United States, 75 million people suffer from walking disorders: stroke, osteoarthritis, arthritis, sarcopenia, poliomyelitis, cerebral palsy, multiple sclerosis, myopathies, etc. These motor disorders cause increased muscle and/or joint weakness. To reduce the progressive loss of locomotor faculties caused by these pathologies, the health authorities recommend a regular and adapted physical activity: walking. To improve the daily life of people with walking disabilities, restore their mobility and extend their walking perimeter, focusing on the knee joint, REEV develops the DREEVEN solution [Temporelli, 2022], a motorization unit for custom knee orthosis.

If many assistive lower limb orthosis are already available on the market [Dollar, 2008], the motorized ones are serial (not custom) exoskeletons which is a problem considering that most people needing motor assistance require custom orthosis. In addition, as presented in [Bernhardt, 2006], patients tend to think that actual serial exoskeletons don't cover all desired use cases, are unwieldy and the mass/volume is not well accommodated on the human body. For these reasons existing serial exoskeletons are not suitable and unattractive for a daily use. In addition, they are expensive; hence, they are mostly bought by dedicated rehabilitation centres. Thus, people lack access to the daily assistive rehabilitation/help they require today.

The DREEVEN solution presented in this article is based on an unobtrusive electrohydraulic transmission which can be integrated on any custom orthosis thanks to its specific mechanical interface designed to fit the morphology of the patient. The solution consists in a motorized hydraulic emitter-receptor cylinder derived from [Temporelli, 2019]. Two hydraulic hoses link the emitter part (the power unit) and the receptor part (transmission mechanism at lower limb level). This principle allows to relocate and spread the mass and volume of the power unit to an appropriate area of the human body (e.g. close to the center of mass for a better body balance) and allows designing a light and slim transmission mechanism at lower limb level. The design of the mechanical transmission also allows to transmits eccentric and concentric torque to the knee, therefore assisting the patient during the entire gait cycle. For these reasons,

the DREEVEN solution allows to power custom knee orthosis with an adequate assistive torque and an adequate bandwidth on the knee in various use cases whilst being slimer and lighter than other marketed systems.

Here, we present the mechanical architecture of the DREEVEN solution and the experimental investigation of its mechanical performances: torque capacities and bandwidth.

## 2. Methods

### 2.1 Dimensioning and target performances

Understanding the kinematics and kinetics of the lower limbs during the different daily activities is fundamental for developing a robotic orthosis. We established a typical profile of a 80kg patient with a healthy gait and focused our attention on walking, ascending/descending stairs and sit-to-stand/stand-to-sit movements. Grounding our calculation on the dataset presented in [Reznick, 2021], we defined our requirements as follows: we aim to assist 30% of the knee torque developed by a 80kg user (approximation of the mean weight of men in Europe) during a 1-second sit-to-stand movement lasting. The worst load case occurs at the 110° knee flexion where a 110Nm knee torque is required. Considering the 30% assistance objective that was based on an estimation of the best power-mass ratio respecting the allocated esthetic volume envelope, and the targeted speed, the system was designed to be able to produce a **33Nm** torque at a **0,5Hz** frequency.

### 2.2 Mechanical design

As previously stated, existing exoskeletons tend to be heavy, bulky, expensive and lack power or use cases coverage. We aim to overcome these drawbacks with our design. After consideration of existing exoskeletons mechanical designs [Shi, 2019], we designed a novel mechanical transmission for lower limb exoskeleton inspired by the electromechanical clutch actuator presented in [Temporelli, 2019]. The presented design relies on an hydraulic transmission functioning as described in Figure 1.

The system is divided in two parts: the emitter (the power unit installed in a bag pack close to the center of mass) and the receptor unit (the transmission mechanism installed on a lower limb custom orthosis). At the emitter level, the motor drives in rotation a ball screw that pushes the ball nut solidary to two pistons using mechanical blades, therefore opening and closing the emitter cylinders. The small chamber of each emitter cylinder is connected to the small chamber of a receptor cylinder that gets opened or closed by the oil transport, and the pistons in their travels pull on a cable therefore resulting in the rotation of the knee pivot. As the receptor is fixed on a thigh orthosis and the knee pivot is linked to a calf orthosis,
the motor rotation leads to a torque being transmitted
to the knee, therefore assisting the patient's gait.

<figure><img src="image_2.png" /><figcaption>Figure 1: Mechanical architecture of DREEVEN</figcaption></figure>

The ‘Results and Discussion’ section
describes the test procedure that allowed us to
validated the defined mechanical objectives.

3. Results and discussion

In order to evaluate its mechanical performances,
the first prototype of the DREEVEN solution was
placed on a test bench. A high stiffness spring was
attached to it with a cable, creating a return force when
the pivot rotated.

<figure><img src="image_3.png" /><figcaption>Figure 2: DREEVEN on its test bench and step
loaded cycle test results</figcaption></figure>

A simple back and forth open-loop control was applied
with 3 different reference shapes (steps, ramp and
sweep sinusoid).

The test bench and experimental results of the 1Hz
loaded step test are presented in Figure 2. The
DREEVEN developed a **34.06 Nm** torque on the pivot
and its response was fast enough to sustain a chirp up
to **1 Hz**, therefore confirming the system's capacity to
reach the desired bandwidth and torque, thus whilst
keeping the mass and volume of the mechanical

assembly to 2170cm3 and 1,5kg in the backpack and
1461cm3 and 1,1kg on the leg These performances can
be compared to [Sanchez, 2019] and classify
DREEVEN has a light exoskeleton for its application
and encourages us to follow our development of
differentiating features by implementing a novel robust
and adaptative control law.

4. Conclusions

We present DREEVEN, a novel concept
overcoming the drawbacks of the lower-limb assistive
exoskeletons present on the market in order to bring a
novel assistive solution to the patients. The electro-
hydraulic transmission divided in a power unit placed
in a backpack and a receptor mechanism interfaced
with a custom leg orthosis allows a better mass
spreading and power density. An experimental
validation phase allowed us to test the mechanical
performances of the system, confirming its ability to
assist 30% of the knee torque developed by a 80kg
patient during a 1 second long sit-to-stand movement.

References

[Temporelli, 2022] Temporelli, R. 2022. U.S. Patent Application No. 17/826,157.

[Dollar, 2008] Dollar, A. M., & Herr, H. ,2008. Lower extremity exoskeletons and active orthoses: challenges and state-of-the-art. IEEE Transactions on robotics, 24(1), 144-158.

[Bernhardt, 2006] Bernhardt, K. A., Irby, S. E., & Kaufman, K. R. (2006). Consumer opinions of a stance control knee orthosis. Prosthetics and orthotics international, 30(3), 246-256.

[Sanchez, 2019] Sanchez-Villamañan, M. D. C., Gonzalez-Vargas, J., Torricelli, D., Moreno, J. C., & Pons, J. L. (2019). Compliant lower limb exoskeletons: a comprehensive review on mechanical design principles. Journal of neuroengineering and rehabilitation, 16(1), 1-16.

[Shi, 2019] Shi, D., Zhang, W., Zhang, W., & Ding, X., 2019. A review on lower limb rehabilitation exoskeleton robots. Chinese Journal of Mechanical Engineering, 32(1), 1-11.

[Temporelli, 2019] Temporelli, R., Boisvert, M., & Micheau, P. 2019. Control of an electromechanical clutch actuator using a dual sliding mode controller: Theory and experimental investigations. IEEE/ASME Transactions on Mechatronics, 24(4), 1674-1685.

[Reznick, 2021] Reznick, E., Embry, K. R., Neuman, R., Bolívar-Nieto, E., Fey, N. P., & Gregg, R. D. 2021. Lower-limb kinematics and kinetics during continuously varying human locomotion. Scientific Data, 8(1), 282.

**Keywords:** exoskeleton, biomechanics, control,
mechatronics, medical robotics

laurence.colas@reev.care