A Vibrotactile Feedback Device for Seated Balance Assessment and Training

Summary

A sitting platform has been developed and assembled that passively destabilizes sitting posture in humans. During the user's stabilizing task, an inertial measurement unit records the device's motion, and vibrating elements deliver performance-based feedback to the seat. The portable, versatile device may be used in rehabilitation, assessment, and training paradigms.

Abstract

Postural perturbations, motion tracking, and sensory feedback are modern techniques used to challenge, assess, and train upright sitting, respectively. The goal of the developed protocol is to construct and operate a sitting platform that can be passively destabilized while an inertial measurement unit quantifies its motion and vibrating elements deliver tactile feedback to the user. Interchangeable seat attachments alter the stability level of the device to safely challenge sitting balance. A built-in microcontroller allows fine-tuning of the feedback parameters to augment sensory function. Posturographic measures, typical of balance assessment protocols, summarize the motion signals acquired during timed balance trials. No dynamic sitting protocol to date provides variable challenge, quantification, and sensory feedback free of laboratory constraints. Our results demonstrate that non-disabled users of the device exhibit significant changes in posturographic measures when balance difficulty is altered or vibrational feedback provided. The portable, versatile device has potential applications in rehabilitation (following skeletal, muscular, or neurological injury), training (for sports or spatial awareness), entertainment (via virtual or augmented reality), and research (of sitting-related disorders).

Introduction

Upright sitting is a prerequisite for other human sensorimotor functions, including skilled movements (e.g., typing) and perturbed balance tasks (e.g., riding on a train). To rehabilitate and improve sitting and related functions, modern balance training techniques are used: unstable surfaces perturb sitting^1,2 and motion tracking quantifies balance proficiency^3,4. Balance training outcomes improve when vibration is delivered to the body using patterns that match performance⁵. Such sensory feedback is evidently....

Protocol

All methods described here have been approved by the Health Research Ethics Board of the University of Alberta.

1. Construction and Assembly of Structural Components

1. Construct an attachment interface for interchangeable hemispherical bases: weld a base nut to a steel weld plate. 
2. Use a computer numerical controlled (CNC) milling machine to construct a cylindrical chassis, lid, and base from polyethylene as shown in Figure 1. Bolt the base plate to the base and the base to the chassis.
   NOTE: The mill features for attachment of bolts and other parts are according to the drawing f....

Results

Table 2 shows, for each experimental condition, the posturographic measures derived from observations of the AP and ML support surface tilts, averaged over 144 balance trials performed by 12 participants (2 x 2 x 3 trials per participant).

Effect of Changing the Balance Condition: The base condition was chosen to be dependent on the eye condition (i.e., when the eyes were closed, the ba.......

Discussion

Methods for constructing a portable, instrumented, sitting device are presented. The device is portable and durable, building on previous studies of wobble chairs^2,4 and vibrational feedback^5,6,7 to make the benefits of these tools more powerful and accessible. Follow the assembly protocol in reverse to prepare the device for transportation or storage. The difficulty of .......

Materials

Name	Company	Catalog Number	Comments
Chassis	McMaster-Carr	8657K421	Moisture-Resistant LDPE Polyethylene Sheet 1-1/2" Thick, 24" X 24"
Lid	McMaster-Carr	8657K414	Moisture-Resistant LDPE Polyethylene Sheet 1/4" Thick, 24" X 24"
Base	McMaster-Carr	8657K414	Moisture-Resistant LDPE Polyethylene Sheet 1/4" Thick, 24" X 24"
Grip-Tape	McMaster-Carr	6243T471	Nonabrasive Antislip Tape, Textured, 6" Wide Strip, 2' Long, Black
Base Nut	McMaster-Carr	90596A039	Steel Round-Base Weld Nut, 5/8"-11 Thread Size
Weld Plate	McMaster-Carr	1388K142	Low-Carbon Steel Sheet 1/16" Thick, 3" X 3", Ground Finish
Threaded Rod	McMaster-Carr	90322A170	3" 5/16"-18 Medium-Strength Alloy Steel Threaded Stud
Sleeve	McMaster-Carr	8745K19	Chemical-Resistant PVC (Type I) Rod 1-1/4" Diameter
Square Flange	McMaster-Carr	8910K395	Low Carbon Steel Bar, 1/8" Thick, 1" Wide
Hitch	McMaster-Carr	4931T123	Bolt-Together Framing Heavy-Duty Steel, 1-1/2" Square
Curved Base	McMaster-Carr	8745K48	PVC Rod, 6" Diameter
Hitch Insert	McMaster-Carr	6535K313	Bolt-Together Framing Heavy-Duty Steel, 1" Square
Extrusion	McMaster-Carr	6545K7	1045 Cold Drawn Steel Square Bar Stock, 1' X 1" Wide, Unpolished
Clamp	Vlier	TH103A	Adjustable Torque Knob
Footrest	McMaster-Carr	6582K431	4130 Steel Tubing, 1" X 1" Wide, 0.065" Wall Thickness, Unpolished Mill Finish
Counterwieght	McMaster-Carr	8910K67	Low-Carbon Steel Rectangular Bar 1-1/8" Thick, 4" Width
Clevis Pin	McMaster-Carr	97245A616	Zinc-Plated Steel Clevis Pin with Hairpin Cotter Pin, 3/16" Diameter, 1-9/16" Usable Length
Microprocessor	Arduino	MEGA 2560	Microcontroller board with 54 digital I/O pins and USB connection
Inertial Measurement Unit	x-io Technologies Ltd.	x-IMU	Inertial Measurement Unit and Attitude Heading Reference System with enclosure
Vibrating Tactor	Precision Microdrives	DEV-11008	Lilypad Vibe Board, available from SparkFun Electronics