Design & Optimization of SPMT for Variable Speed Gait TrainingN.B. Patel, T. J. Dalbora, Derek Lura Ph.D

Department of Bioengineering, U.A. Whitaker College of Engineering, Florida Gulf Coast University

The goal of this research is to develop a self-paced motorized treadmill (SPMT)

that can simulate over ground-walking, to improve the effectiveness of treadmill

training. The use of a SPMT provides a safe and reliable environment for

intensive gait analysis. The SPMT utilizes an external open-source

microprocessor and an ultrasonic range finder, as shown in figure 2, which

detects the distance of the closest object (up to 5 m) in front of the sensor. The

range finder is mounded on the top console of the treadmill, as shown in figure4,

and is used to monitor the user’s distance from the console. The user’s position

dictates the velocity. A Pulse Width Modulation (PWM) signal is used to control

the treadmill interfaces and an electric motor, which activates belt movement.

Treadmill based training has been shown to be an effective method to improve

walking characteristics for rehabilitation [1,2]. Gait training of severely affected

patients after a stroke or injury is usually difficult due to their loss of balance and

motor function. In addition to the difficulties of gait therapy, traditional fixed-

speed motorized treadmill walking may not simulate natural walking because of

fixed belt speed; once the speed is set, the speed remains constant. As shown

in figure 6, the result shows that the velocity and duty cycle are successfully

modulated based on position of the subject. The optimization of SPMT can be

greatly beneficial for gait therapy in future. However, additional quality controlled

studies are needed before SPMT can be used for widespread therapy.

The SPMT research is unique in that, unlike most SDTT related to gait

rehabilitation, the variable speed change can speed up the improvement

neuroplasticity and motor functions. The SPMT demonstrates that subjects can

experience natural walking ability (e.g. stride length, step counts) on treadmill.

For stroke patient, with very limited gait abilities, the SPMT can tolerate

treadmill training without the necessity of partial body-weight support, while

reducing the belt friction and eliminating constant speed problem. SPMT can

significantly improve both functional mobility and cardiovascular fitness in

patients with chronic stroke, and is more effective and beneficial than reference

rehabilitation common to conventional care.

[1] Schwartz I, Sajin A, Fisher I, Neeb M, Shochina M, Katz-Leurer M, Meiner Z. The effectiveness of locomotor

therapy using robotic-assisted gait training in subacute stroke patients: a randomized controlled trial. PMR

2009; 1:516-523.

[2] Veerbek JM, Van Wegen EEH, Hermeling-Vanderwel, Kwakkel G. Is accurate prediction of gait in non-

ambulatory stroke patients possible within 72 hours post stroke? The EPOS study. Neurorehabil Neural Repair

2011; 25(3):268-274.

[3] Behrman, AL and Harkema, SJ. Locomotor training after spinal cord injury: A series of case studies. Physical

Therapy. 2000; 80 (7):688-700.

[4] Paavolainen L, Hakkinen K, Hamalainen I, Nummela A, Rusko H. Explosive-strength training improves 5-km

running time by improving running economy and muscle power. J Appl Physiol. 1999; 86: 1527–1533.

[5] P.Bhagwat, and V.R.Stefanovic, “Generallized structure of a multilevel PWM Inverter,” vol.1A-19, no.6,

pp.1057-1069. Nov./Dec..1993

PWM: Electric motor speed is controlled by increasing and decreasing the

voltage to the motor. More voltage and the motor rotates faster, less voltage

and the motor slows down, figure 1.

Figure 1: Nomenclature and Electrical circuit model of PWM duty cycle; when

the duty cycle is 0%, the load (motor) is fully off; when the duty cycle is 100%,

the load is fully on [5].

Abstract

Introduction

Conclusion

References

System Set UP

Figure 2: Timing diagram and electrical circuit model of Ultrasonic Ranging Module

(HC-SR04), connected to treadmill. HC-SR04 provides 2cm - 400cm non-contact

measurement function, the ranging accuracy can reach to 3mm. The modules

includes Ultrasonic transmitters, receiver and control circuit.

Figure 3 : Shows the modified treadmill;

user is demonstrating SPMT parameters.

Discussion

Treadmill training can significantly improve the outcome of gait therapy. Speed-

Dependent Treadmill training is a physiologically based approach to retraining

ambulation after life threating injuries such as a stroke, which capitalizes on the

intrinsic properties of motor functions. For seriously distressed patients who

cannot walk under their own power, treadmill training with body weight support is

clinically recommended [2]. In SPMT, gait velocity is fluctuating based on the

patient’s position on treadmill. Recent training techniques for stroke patients

have begun to include sport physiological approaches such as aerobic exercises

and circuit training [3]. Sport physiological research has indicated that training at

speeds below the trainee’s maximum speed does not provide optimal

improvements in gait speed. Only increasing sprint training at maximum speed

brings about optimum gait improvement [4]. SPMT allows patient to maintain

balance and improve appropriate gait kinematics while at the same time

promoting continuous stepping. SPMT can provide treadmill training that can

simulate over ground walking that can be more effective than conventional gait

training for improving gait parameters.

System Calculations

VCC : +5V, TRIG :Trigger In,

ECHO: Echo Out & GND: Ground

Figure 4 : Physical prototype of HC-SR04

circuit model.

Pulse Width: Time the signal is

in the ON or high state (sec)

Period: Time of one cycle (sec)

Future Study

Additional research is needed to demonstrate the efficacy of SPMT. The subject

interaction and adaptations of SPMT also requires further investigation. Finally,

more rigorous studies are needed to determine the effectiveness of SPMT and

the recommended parameters for gait rehabilitation (e.g., treadmill speeds,

amount of body-weight support, session length and frequency, optimal duration

of treatment). An additional treadmill modification will include an interface of an

virtual reality system that can provide an engaging environment that could

motivate the stroke patient to relearn basic cognitive skills.

Further Modifications

of SPMT

Introduction of Virtual

Reality

Subjective Locomotors

Training

Stroke or Gait

Disability

𝐃𝐮𝐭𝐲 𝐂𝐲𝐜𝐥𝐞 = 𝟏𝟎𝟎% ∗𝐏𝐮𝐥𝐬𝐞 𝐖𝐢𝐝𝐭𝐡

𝐏𝐞𝐫𝐢𝐨𝐝

Results

0.1

1.52

2.41

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5.666.18

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Treadmill Duty Cycle (%)

Velocity - Duty Cycle Relationship

Reed Switch Velocity

Qualisys Velocity

Figure 5: Velocity of the treadmill at steady state versus duty cycles. Velocity was

determined using a reed switch and an Arduino microcontroller, and values were

verified using Qualisys Track Manager.

Figure 6: (A) The treadmill velocity changes when the duty cycle changes with

respect to time. (B) As the user gets closer to the console, the treadmill speeds up.

As the user backs away from the console, the treadmill slows down.

The graph in Figure 5 demonstrates that the velocity obtained using the reed

switch is accurate. The velocity was obtained using the Qualisys Track

Manager, by exporting the raw position data to MATLAB and obtaining the

derivative of the position vector. Using the HC-SR04 sonar range finder, the

position of the user, as shown in figure 3, can be measured, and the velocity of

the treadmill is modulated based on the distance the object is to the console.

As shown in Figure 6, when a person or object is directly in front of the sonar

range finder, the treadmill program will modulate the speed such that the object

remains at a fixed distance away from the control console. The velocity of the

treadmill is modulated by the duty cycle of the motor, which is controlled by

pulse width modulation sent from the Arduino.

Figure 7: Demonstration of the wave

propagation of the range finder that

modulates the speed.

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Duty & Velocity vs Position

Duty Velocity

01122334455

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Duty & Velocity vs Time

Duty Velocity

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A B

Benefits of SPMT

Limit workload for the therapist(s).

Provide a safe environment for the patient and therapist.

Allows for gradual introduction of body weight to gait training.

Allow for more focused and technical practice.

Patients can rehab at automatic varying speed.