Editorial Feature

Building a Robotic Arm

A robotic arm is a kind of mechanical arm that can be programmed with functions similar to a human arm. The arm may either represent the complete mechanism or be part of a more complicated robot. The manipulator joint enables linear displacement or rotational motion. The manipulator links form a kinematic chain. The end point of the kinematic chain is known as the end effector, which is similar to the human hand. The robotic hand or the end effector can be designed to do any task like spinning, gripping, welding, etc., based on the application.

Research

In 2009, Blackmore M and his team of researchers from Portland State University designed and built a mobile robot capable of behavior like humans. The team designed an arm and hand assembly along with designing the robot base, the head and neck to supplement the gestures of the robot and help it to grasp and move objects.

The arm was designed to satisfy the following criterion:

  • It must be able to grasp an object and place it in a different location
  • It must have a similar scale as a human arm and must be able to simulate motions
  • The final design must be made with standard components so that it can be conveniently reproduced to make two versions
  • The arm should be mounted easily to the mobile base.

The purview of the project involved the development of an arm and the range of motion of each joint associated with this arm. System modeling relates to the hand position to the joint angles in the arm. Software design encompasses the programming methods for commanding actuators to move a joint to a specific position along with a description of the programming environment. The electrical components include the hardware needed to power and control the system, actuators as well as devices to send a command signal.

Presently, NIH scientists are constructing robotic arms that can provide training and physical therapy assessment to patients whose muscles have been weakened by traumatic brain injury (TBI), cerebral palsy or other neurological disorders. Such technology will also be able to operate these machines remotely. For instance, it will be possible for a clinician in the office to provide therapy to a patient at home.

These rehabilitation robotic arms will help patients by evaluating muscle-related tasks or for training of weakened muscles to regain their strength. The design and development of these robots is being led by Hyung-Soon Park, a staff scientist at the CC’s Functional and Applied Biomechanics Section (FABS).

Two robotic mechanisms were developed by Park’s lab working together for the rehabilitation of the elbow joint. The development process involved a human arm (haptic mannequin device [HMD]) that depends on the sense of touch. This is attached to a computer in the office of the clinician. The second stage involves a wearable stretching device (WSD). This robotic tele-rehabilitation system will benefit patients suffering from involuntary muscle spasms caused by neurological impairments. This HMD-WSD setup helps the physician to move the HMD mechanical arm. Through the Internet a signal travels to the patient; the WSD arm brace being worn by the patient imitates the movement and stretches the muscles.

Muscle resistance is recorded by the WSD and the data is relayed back to the HMD so that it moves and feels like the patient’s arm. The two devices constantly communicate and it is as if the clinician and patient are in the same room.

The Rehabilitation Robotics Lab, lead by Dr. Redwan Alqasemi, is a great example of work that involves the development of a 9 degree-of-freedom wheelchair mounted robotic arm that is manipulated using a brain–computer interface system to help the user gain a sense of control following the loss of a limb (see video below).

Current Applications

Present applications of the robotic arm include the following:

Gantry or Cartesian robot: This robotic system is used for pick and place work, assembly operations, arc welding and handling machine tools. The arm component to this system has three prismatic joints with axes coincident with a Cartesian coordinator.

  • Cylindrical robot: used for their application in the assembly of components, and maintaining operation at die-casting machines.  
  • Polar or Spherical robot: This robot is ideal for die-casting, handling at machine tools, and arc welding. The axes to this robotic system form a polar coordinate system.
  • SCARA robot: This is used for applying sealant, pick and place work, handling machine tools and assembly operations. It is a robot with two parallel rotary joints to provide planar compliance.
  • Articulated robot: systems used for the application of die-casting, assembly operation, and spray painting. There are three rotary joints to this robotic arm.
  • Parallel robot: Parallel robots function on cockpit simulators. The arms to this robotic system have concurrent rotary or prismatic joints.
  • Anthropomorphic robot: a more complex version of a robotic system. This device closely resembles a human hand with independent functions to the fingers and thumbs based on the complexity of the joint function.

Future Developments

A new study published in Nature in May 2012 reported that two persons having tetraplegia reached for and held objects in three-dimensional space with the help of robotic arms that were directly controlled with brain activity. The BrainGate neural interface system was used, which is an investigational system that is being evaluated under an Investigational Device Exemption. This system was used by a person to serve coffee since paralysis 15 years ago. If brain-controlled robotic arms get commercialized, these will enable considerable improvement in quality of life in patients having paralysis and help harness the power of a healthy brain.

The robotic arms built by Canada for the International Space Station and NASA’s space shuttle fleet will be receiving two more members in its family. The Canadian Space Agency demonstrated the advanced Canadarm prototype at Canadian company MacDonald, Dettwiler and Associates that was displayed after 3 years of development. The mechanical limbs succeed the station’s Canadarm2 and the shuttle fleet’s Canadarm that played key roles in the construction of the station for over a decade.

The MDA and CSA intend to utilize this technology to position Canada for novel business opportunities in areas such as in-orbit refuelling of satellites according to the  agency's director-general of space exploration, Gilles Leclerc.

Sources and Further Reading

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