Polytechnique Laboratory for Assistive and Rehabilitation Technologies (POLAR) Application Story

Led by Professor Anolfazl Mohebbi, POLAR, is a Montreal-based laboratory for assistive and rehabilitation technologies, where next-generation end-effector robots are being pioneered. Traditional rehabilitation methods pose a significant challenge to healthcare providers and often lack the frequency and intensity necessary for optimal therapeutic outcomes. Robotic-assisted haptic therapy has emerged as a promising alternative and addresses these limitations by delivering precise, repetitive, and customizable movements that enhance consistency and generate valuable treatment data. Most of the robotic systems available are designed to treat patients with spinal cord injuries, whereas this project focuses on advanced robotic solutions designed for neuromuscular rehabilitation through an end-effector robot. 

The Challenge: High-Speed, Long-Stroke Linear Actuation in a Compact and Lightweight Rehabilitation System 

Designing robotic systems for physical rehabilitation presents a unique set of engineering challenges. Unlike industrial robotics, where speed and precision are prioritized in isolation, rehabilitation robots must interact directly with the human body to deliver controlled motion and force while remaining inherently safe, compliant, and intuitive. This is particularly important when working with patients who have neuromuscular diseases, where strength, coordination, and responsiveness may vary widely between individuals and over the course of treatment. Finding the right linear actuator for the project’s end-effector robot was a challenge for the team as speed, stroke, size, and weight were important requirements of the motor. Actuators available in the market were either too slow and heavy, or if they did meet speed requirements, usable stroke was compromised. 

Many commercially available actuators that met the required speed lacked sufficient stroke, often offering only limited travel ranges unless paired with external gearing or mechanical extension systems. These additions would increase system mass, introduce backlash, and complicate dynamic control. For example, peak hand velocities during rapid upper-limb reaching movements in healthy adults commonly range from 0.5 to 1.0 meters per second, depending on the task and distance. Replicating this in a robotic system without sacrificing stroke proved difficult. Actuators capable of longer travel were often too large or too slow to deliver quick, consistent motion under load. “There are essentially no actuators that can give you that kind of speed, but at the same time give you a functional stroke,” said project lead Thomas.

Adding to the complexity was the need for backdrivability and closed-loop force control, both critical for delivering compliant, user-responsive motion. Patients undergoing rehabilitation must be able to interact with the system safely and naturally, whether passively receiving guided movements or actively resisting applied forces. That requires smooth control of force and position, with low to no mechanical impedance (cogging/torque ripple). Legacy systems rely on externally mounted load cells, position encoders, controllers, amplifiers, and motor drivers. All of these increase time, cost, complexity and system latency. The robot’s 3DoF configuration supporting horizontal, vertical, and rotational movement, added further design constraints. Each axis required its own actuator which meant multiple power supplies, amplifiers, wiring, and cabling, all of which expanded the system’s physical footprint. During the actuator selection process, the team noted that online specifications rarely accounted for the real-world space required once ancillary electronics were installed. Even actuators marketed as compact often became impractically large once full control stacks and wiring harnesses were added.

ORCA-3-12V Linear Actuator as an Ideal Solution

Recognizing the limitations of traditional linear actuators, the team turned to ORCA motors as a fully-integrated, high performing solution capable of safely supporting dynamic human-robot interaction. In their search they found the ORCA-3-12V to be the only actuator capable of replicating the speed of upper-limb movement while offering a usable stroke length sufficient for full arm extension. ORCA-3-12V can reach speeds of 8.1 m/s, and offer a usable stroke of 101.6 mm. ORCA-3’s unique balance of speed, precision, and integration made it the clear choice for this innovative rehabilitation system.

The team is developing a 3DoF end-effector robot designed to assist patients with neuromuscular diseases, with a goal of making rehabilitation more accessible and effective, allowing patients to safely perform targeted therapeutic exercises independently. The robot uses a combination of three actuators (one rotational and two translational) to support movement across the three axes: horizontal, vertical, and rotational. The ORCA-3-12V actuator is deployed on the horizontal axis, where its speed, compact size, backdrivability, and smooth force control make it uniquely suited for replicating natural upper-limb motion.

• Compact & Light Weight: The ORCA-3’s compact dimensions (measuring 9 inches in length) and light weight nature made it ideal for a portable system. The team aimed to create a rehabilitation device that patients could eventually use in their homes, making weight and form factor critical. Unlike many actuators whose true footprint expands significantly once power supplies and cabling are added, the ORCA-3 maintains a compact, self-contained profile that supports simple real-world deployment beyond the lab.
• Precision for Human-Robot Interaction: The system required actuators capable of responsive, precise motion for effective and safe human-robot interaction. The ORCA-3 delivers high-speed force and position control, enabling the fine-tuned haptic feedback essential for upper-limb rehabilitation and robotic assistance. Its compliant, backdrivable nature and lack of cogging or torque ripple ensures safe operation even in direct physical interaction with the user.
• Real-Time Sensing and Feedback: Built-in position and force sensors eliminate the need for external sensing components, streamlining both system architecture and data accuracy. This integrated sensing capability enables real-time data capture allowing the team to monitor patient progress across treatment sessions. By capturing detailed force profiles, kinematics, and user responses, the ORCA-3 supports the development of adaptive therapy protocols and detailed performance tracking.
• Affordability for Broader Accessibility: Most robotic rehabilitation systems are priced out of reach, often exceeding $100,000 per unit. ORCA-3 offers integrated drivers, PID controllers, and sensors at volume pricing below $1,000 supporting POLAR’s mission of delivering a more affordable, and accessible solution for patients and healthcare providers. 

Technical Specifications

The rehabilitation system is powered by a 3DoF end-effector robot that incorporates one rotational and two translational actuators to enable horizontal, vertical, and rotational movements. Key technical features of the ORCA-3-12V actuator used in the system include:

Integrating the ORCA Motor into End-Effector Cobot

The ORCA-3-12V actuator handles horizontal motion in the 3DoF end-effector rehabilitation robot. It works in tandem with a belt-driven actuator for vertical movement and a rotary actuator for rotation. Integrated to deliver precise linear motion, the ORCA was initially tested using IrisControls for communication and basic validation. The team will shift to synchronized control via C++, enabling real-time position and force commands across all actuators. With built-in sensing, back-drivability, and a compact design, the ORCA reduced system complexity and removed the need for external feedback hardware. Its combination of long stroke and responsive speed supports full-arm extension and high-intensity training, making it suitable for both neuromuscular and spinal cord injury rehabilitation.

The Role of Haptics in Robotic Rehabilitation

Haptic technology plays a foundational role in modern robotic rehabilitation by enabling systems to simulate touch, force, and motion in ways that are both responsive and therapeutic. In neuromuscular recovery, where patients often struggle with impaired motor control or reduced sensory feedback, haptics allows robots to deliver tailored, interactive experiences that promote engagement and neuroplasticity. Unlike passive machines, haptic-enabled systems can both sense and respond to user input in real time. This bi-directional interaction allows for adaptive therapy where the robot adjusts its force, resistance, or motion based on the patient’s effort and feedback. Whether guiding a limb through a predefined trajectory or resisting motion to build strength, the precise force control enabled by haptics is essential for safe and effective therapy.

The ORCA-3-12V actuator used in the system includes integrated force and position sensors, allowing the robot to deliver high-fidelity haptic feedback without requiring bulky external components. This built-in sensing not only reduces system complexity but also ensures lower latency and higher responsiveness, critical attributes for real-world human-machine interaction. By capturing detailed interaction data such as force profiles, joint kinematics, and response timing, the system can also generate rich insights into patient progress over time. These capabilities position haptics not just as a control feature, but as a diagnostic and therapeutic tool that supports more intelligent, personalized rehabilitation.

Final Thoughts: Expanding Therapeutic Possibilities

The responsive force feedback and dynamic capabilities of the ORCA-3 actuator have opened the door to new high-intensity exercise routines not previously feasible with standard rehabilitation tools. Its ability to precisely mirror human motion expands the potential for more engaging, effective therapy experiences.

By integrating high-speed actuation, compact design, and real-time haptic feedback into a portable platform, the team at POLAR has developed a solution that not only meets clinical performance standards but will also adapt to in-home and remote care environments. This advancement moves robotic rehabilitation beyond research settings and into everyday use, offering patients greater autonomy and access to consistent, high-quality therapy. As haptics and assistive robotics continue to evolve, systems like this one demonstrate how thoughtfully integrated engineering can directly improve patient outcomes, making cutting-edge research and real-world care more accessible.