The field of rehabilitation has been encountering various advancements in recent days. One of such technologies is known as HAS, expanded as Hybrid Assistive System.

What is HAS?

As the name suggests, HAS is a hybrid system. HAS is the combination of FES (Functional Electric Stimulation) and an externally controlled and powered brace known as the hybrid assistive system. According to the thoughts of the wearer, the HAS skeleton moves.

HAS works under the principle of bio-cybernic control. Biocybernic refers to the control and communication system of living organisms. The muscles receive the myoelectric signals from the brain. These signals are detected by the bioelectrical sensor and this activates Biocybernic control. This control system reads data and activates the suit motors accordingly.

History of HAS

1993Discovery and mapping of neurons that governs leg movement
1996Prototype HAL-1 was designed and created which only supported the lower half limb
1997Prototype HAL-3 was designed and created which was attached to a computer
1999The HAL-3 prototype was released for trail, which has a backpack battery that weighed 22kg
2003Prototype HAL-5 was designed and the computed was attached directly to the suit for limb control system
2005The HAL-5 prototype was released for trial, which has a waist strapped battery that weighed 10kg
2011The HAL-5 was certified in Medical Device Directory for European Conformity
2012HAL-5 was commercialized in hospitals and rehabilitation centers.

Future improvement of HAL suits

There can be an improvement in the HAL suits by the following considerations

  • Operation time improvement
  • Sensor performance enhancement
  • The cost of materials should be low
  • The cost of production should be low

Applications of HAS

  • Next generation rehabilitation: This is done by enhancing, accelerating, and supporting the physical capabilities of the user, wearer’s daily activities and improves recovery.
  • Disaster relief activities: This can be used as a rescue system at disaster sites. HAS helps in accelerating disaster recovery activities, saving lives, lifting heavy obstacles and victims, and disaster cleanup
  • Heavy industries: HAS is used in supporting the workers to carry heavy machines. This in turn helps in the reduction of the injury to improper handling of heavy items.
  • Hospitals and nursing homes: HAS helps in the improvement and mobility of the elderly and the disabled.

MARCUS – Intelligent hand prosthesis

MARCUS is expanded as Manipulative Automatic Reaction Control and User Supervision. It is the prosthetic hand that is controlled by the user through the use of myoelectric sensors. The microcontroller controls the hand and objects interaction automatically through,

  • Position sensors
  • Force sensors
  • Slippage sensors

Many artificial hands are successful in use but have only a limited degree of freedom. Due to the application of mechatronics and principles to artificial hands, it is possible to control a more complex and functional hand.

MARCUS is advantageous over the traditional myoelectric hand and brain-controlled hand as visual feedback, local feedback, and sensory feedback are available. Local feedback is not available in the brain-controlled hand and no feedback is available in the traditional myoelectric hand.

The hierarchical control system of MARCUS

Two degrees of freedom are possible with the hands, finger flexion, and thumb flexion. Three fingers: a thumb, an index finger and a middle finger is present in the hand while the last two are connected at the base of the phalanxes. The thumb is driven by a motor and the index and middle fingers are driven by another motor.

The fingers and the palm of the hands have sensors. This enables the recognition of the object held in the hand and the possible slipping of the same. The EMG signals are used to control the motors of the hand. These motors operate in such a way that ensures optimal contact and increases the strength of the grip.

The sensors used in MARCUS are as follows:

  • Force sensors
  • Palm sensors
  • Kinesthetic sensors
  • Slip sensors

Force sensors

These sensors are located at the fingertips of three fingers. A maximum load of 120N is the withstanding capacity of the force sensor.

Palm sensors

These sensors are used to detect the object’s contact occurring between the palms and the prosthetic hand. There are two possible types of grasp configurations that can be performed. FSR sensor is used as the palm sensor. The degree of rotation can be determined by the pressor sensors along the fingers.

Kinesthetic sensors

This provides the control system with geometrical information about the grasping configuration. The hall effect sensor is fixed to the metacarpus phalangeal joint.

Slip sensors

These sensors are integrated at the fingertips. To detect the vibrations produced by the slippage of the object, a small microphone is attached.

Control system of MARCUS

Position: When the muscle relaxes, the hand closes. This is because the degree of opening of the hand is proportional to the muscular tension. The palm sensors detects the shape of the object. This makes the controller select the grip posture to suit the shape.

Touch: There are detailed corrections made by the controller to suit the exact shape of the object. This decreases the contact force and increases the contact area.

Hold: The user instructs the computer to hold the object. There are two types of grips,

  • Precision grip
  • Power grip

If the grip tension is too low, the object slips. This is detected by the sensors on the hand which results in an increase in the force. This force is directly proportional to the time that slippage occurs.

Squeeze and release

The operator can instruct the hand to either open the hand to release the object or to close the hand to maintain a proper grip.

Park:

Finally, after the task is complete, the hand is disabled and the system is shut down to conserve power.

Thus the basic principles of HAS have been discussed in detail.

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