Project
| # | Title | Team Members | TA | Documents | Sponsor |
|---|---|---|---|---|---|
| 48 | Low-Cost Wearable Bilateral Teleoperation Platform with Grip-Force Feedback |
Godrein Owusu-Ayeyi Junghyun Kim Junseo Kim |
Junyan Bai | ||
| # Low-Cost Wearable Bilateral Teleoperation Platform with Grip-Force Feedback **Team Members:** - Junseo Kim (junseok3) - Godrein Owusu (gowus2) - Junghyun Kim (jk61) ## Problem Many tasks require a person to manipulate objects without being physically present in the operating environment. Hazardous material handling, remote equipment inspection, and disaster response are common examples. A conventional camera-and-joystick teleoperation system provides visual information but gives the operator little physical information about contact. The operator cannot feel when the gripper touches an object or how strongly it is being held, which makes delicate manipulation difficult: too little force lets an object slip, and too much force damages a fragile one. The appropriate force also depends on what is being held, since a grip that securely holds a rigid object will crush a thin-walled cup. Commercial bilateral teleoperation systems address these problems using multi-axis force/torque sensors and torque-controlled actuators, but such systems are expensive and mechanically complex. We plan to build a small, low-cost proof-of-concept platform that demonstrates the same core capabilities: wearable motion sensing, robotic motion reproduction, bidirectional communication, grip-force sensing, haptic feedback, and automatic grip-force protection. The goal is not a system for actual hazardous, medical, or military use, but a demonstration of the electrical and mechanical subsystems that human-in-the-loop teleoperation requires. ## Solution The system will consist of a wearable leader and a three-axis robotic follower with a gripper. The user will wear a lightweight passive mechanical frame carrying four position sensors: two for shoulder motion, one for elbow motion, and one for thumb and index finger motion. The two shoulder measurements will represent left-right and up-down arm movement and will control the follower's rotating base and shoulder joint. The elbow sensor will control the follower elbow, and the finger sensor will control the gripper. The leader microcontroller will acquire and filter these measurements, convert them into joint commands, and transmit them over a wired link to the follower microcontroller, which will generate the corresponding servo commands. Forward: user motion → leader sensors → leader MCU → wired link → follower MCU → servos → robot motion Reverse: object contact → FSR → follower MCU → wired link → leader MCU → vibration motor → operator This bidirectional sensing and feedback loop is the primary feature that makes the system a bilateral teleoperation platform. The follower will also use the force measurement for local protection. As the gripper closes, the controller will estimate how compliant the grasped object is and select a force limit appropriate to that object, so that a paper cup is protected with a lower threshold than a rigid block without the operator specifying what is being held. If that limit is reached, the controller will override the operator's closing command. The link will be wired rather than wireless. This avoids the added latency, packet loss, interference risk, and battery requirements of a wireless link, and lets the wearable device draw power through the same cable so the user carries no battery. ## Solution Components ### Wearable Leader and Position Sensing Subsystem A lightweight passive frame worn on the arm will carry rotary position sensors at its joints. Two sensors on perpendicular axes will measure the two major directions of shoulder movement, a third will measure elbow bending, and a fourth will measure thumb and index finger motion. The frame is not intended to reproduce exact anatomical joint angles. The human shoulder is a ball joint whose center of rotation lies inside the body, so some residual misalignment is unavoidable. Our requirement is instead that the mapping from user pose to sensor reading be repeatable and monotonic, with a startup calibration routine mapping each user's range of motion onto the follower's joint range. A clutch button will let the operator stop sending commands while repositioning their arm. *Proposed components:* - STM32F103C8T6 microcontroller - Four rotary potentiometers - Analog filtering and buffering - Clutch push button - 3D-printed frame with adjustable links and straps ### Follower Robotic Arm and Gripper Subsystem The follower will be a three-axis robotic arm with base rotation, shoulder rotation, elbow rotation, and a two-finger gripper, driven by four servo motors. Software joint limits, slew-rate limits, and mechanical stops will prevent unsafe or unstable movement. Because the follower has no actuated wrist, the gripper's orientation would otherwise change as the arm reaches farther or closer. A passive parallelogram linkage in the forearm will hold the gripper at a near-constant orientation across the working range, without requiring an additional servo. A position sensor on the gripper joint will measure actual finger position rather than relying on the commanded servo angle, since a loaded servo does not reach its command. *Proposed components:* - STM32F103C8T6 microcontroller - Four metal-gear servo motors - Gripper joint position sensor - 3D-printed arm links, gripper, and parallelogram linkage - Mechanical joint stops ### Grip-Force Sensing and Adaptive Force Limiting Subsystem An FSR beneath a compliant pad inside one gripper finger will detect contact and provide a relative measure of grip force. Because the FSR response is nonlinear, it will be characterized against known loads and used to identify relative force levels rather than absolute values. Once contact is detected, the gripper's closing rate will be reduced and the controller will record the gripper joint angle as the measured force crosses a low and then a high reference level. The difference between these angles gives a compliance index: ``` D = theta(F_high) - theta(F_low) ``` A rigid object requires little additional closure for force to rise between the two levels, producing a small D; a compliant object deforms further and produces a large D. Because both endpoints are fixed points on the FSR curve, D does not depend on absolute force calibration, and measuring the true gripper angle rather than the commanded servo angle removes the servo's own compliance from the result. Reference objects will be tested during calibration to establish classification boundaries, with the number of distinguishable classes determined by the measured separation. Based on the estimated class, the follower will select a grip-force limit and hold the gripper position if that limit is reached. *Proposed components:* - Force-sensitive resistor - Compliant silicone pad - Signal-conditioning circuit - Reference objects spanning a range of compliance ### Communication, Control, and Haptic Feedback Subsystem The leader and follower will each use a separate microcontroller. Placing a microcontroller on the wearable device keeps analog sensor traces short and allows only digital data to travel down the cable. The two will communicate over a bidirectional wired serial link using a fixed packet frame with an error-detecting checksum, so corrupted packets can be rejected rather than applied to the servos. The leader-to-follower packet will carry joint targets, the gripper target, and the clutch state; the follower-to-leader packet will carry contact and force information and a system status field. A small vibration motor near the operator's index finger will be driven with PWM, with intensity increasing with the measured force. At minimum the system will distinguish no contact, light grip, and strong grip. If the follower does not receive a valid packet within a defined timeout, it will enter a safe state and prevent further gripper closing. *Proposed components:* - Bidirectional wired serial link with checksum - Coin-style vibration motor and transistor driver - Microcontroller watchdog timers ### Power and Safety Subsystem The system will run from an external wall supply rather than batteries. A servo rail of approximately 6 V will power the follower servos, and a separate regulated logic rail will power the microcontrollers and sensors. The leader will receive low-voltage power through the communication cable so the user wears no battery. Servo and logic power paths will be separated so that servo current transients cannot reset the microcontrollers, with bulk capacitance near the servo connectors and local decoupling at the supplies. Planned protections include a physical emergency-stop switch that disconnects servo power without depending on software, a communication timeout and safe state, software joint-angle limits, mechanical joint stops, servo slew-rate limits, grip-force limiting, and overcurrent protection on the servo rail. The wearable frame is fully passive apart from the vibration motor, which cannot apply injurious force. *Proposed components:* - DC input from a wall supply - Buck converter for the servo rail - Regulator for the logic rail - Reverse-polarity protection and input filtering - Emergency-stop switch ### Custom PCB Subsystem The design will use two custom PCBs, one on each side of the cable. This keeps the analog sensor traces short on the leader, allows the cable to carry only power and a digital link, and places servo current transients on a physically separate board from the sensor front ends. The leader board will carry the leader microcontroller, the buffered and filtered position-sensor inputs, the clutch input, the vibration-motor driver, the serial interface, and local voltage regulation. The follower board will carry the follower microcontroller, the servo drive connections, the FSR signal-conditioning chain, the gripper-position sensor input, the serial interface, the servo and logic rails with separated return paths, and supply protection. ## Criterion for Success - The follower base, shoulder, and elbow reproduce the corresponding leader motions with a mean angular error of 5 degrees or less over the calibrated range. - Command latency from leader sensor acquisition to follower servo-command update is below 20 ms. - The gripper responds to the user's finger motion, and the arm moves an object of at least 100 g between two marked locations in at least 8 of 10 trials. - The haptic system produces feedback that a blindfolded user can use to distinguish no contact, light grip, and strong grip in at least 80% of trials. - When the selected force limit is reached, the follower prevents further gripper closing even while the operator continues to command it closed. - The system distinguishes between reference objects of clearly different compliance and applies a correspondingly different force limit. - The system moves an empty paper cup between two marked locations without permanently crushing it in at least 8 of 10 trials. - The follower enters a defined safe state when the communication link is disconnected. ## Reduced-Scope and Contingency Plan If the two-axis wearable shoulder mechanism does not achieve sufficient repeatability, the shoulder measurements will be replaced by measurements taken entirely on the arm, such as forearm rotation and wrist flexion, which are simple hinge or coaxial rotations requiring no torso reference and which map onto the same follower axes. Repeatability will be measured early, on a breadboard with a single joint, so this decision can be made before the mechanical design is finalized. If the compliance-estimation method does not separate the reference objects reliably, force limiting will use a fixed threshold instead, with contact sensing, haptic feedback, and force protection all remaining functional. This will also be evaluated early with a single servo and a single FSR. If the arm does not provide sufficient torque, link lengths or the payload requirement will be reduced while preserving the complete leader-follower and force-feedback system. If a custom PCB requires revision, development boards and external signal-conditioning circuits will be used temporarily while the fault is documented and corrected. The minimum functional demonstration will include three-axis leader-follower motion, gripper control, grip-force sensing, vibration feedback, fixed-threshold force limiting, and communication-loss protection. ## Relationship to ECE 398 Independent Study Two members of this team, Godrein Owusu and Junghyun Kim, are also enrolled in a separate ECE 398 independent study on robotic teleoperation, with approval to take both courses. Junseo Kim is not part of the ECE 398 project. We identify this explicitly because the two projects may share the same physical robotic platform. **ECE 445** asks whether a low-cost wearable bilateral teleoperation system can reproduce operator motion, sense remote grip force, return haptic information to the operator, and protect objects from excessive gripping force. Its scope is the complete physical and embedded system, including the wearable frame, the follower arm and gripper, force and position sensing, haptic feedback, compliance estimation and adaptive force limiting, bidirectional communication, custom PCB design, power, and safety. The adaptive input is object compliance and measured grip force, and the adaptive output is the allowable grip-force limit. The deliverable is the working hardware platform. **ECE 398** asks how motion scaling affects the speed-precision tradeoff in teleoperation, and whether operator-velocity-based adaptive scaling improves performance over fixed scaling. It uses the platform as an experimental testbed. The adaptive input is operator movement velocity, and the adaptive output is the leader-to-follower motion-scaling ratio. The deliverable is experimental data and analysis. The separation is along a clear line. ECE 445 addresses the physical interaction between the follower and the object; ECE 398 addresses the mapping between operator motion and follower motion. ECE 398 does not address grip-force sensing, object compliance, haptic feedback, adaptive force limiting, PCB design, or construction of the robotic arm, and will not claim any of these as its research contribution. The ECE 398 algorithm is not required for the ECE 445 system to satisfy its requirements or pass its final demonstration. Within the ECE 445 team, the subsystem that constitutes the project's adaptive contribution, together with the haptic feedback path, is owned by Junseo Kim, who is not enrolled in ECE 398. ECE 398 experiments will begin only after the ECE 445 system has passed its motion-reproduction and communication verification, so the two projects do not compete for the platform during ECE 445 integration and debugging. ECE 445 retains priority access to the hardware through its final demonstration. |
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