Thought-controlled robots power us up
31st Aug 2008 | 20:00
How robotics is enhancing our mobility, strength and precision
Robotic technology is increasingly relevant to the entire healthcare sector. And the need for assistive robotic devices is set to increase dramatically as the demographic shift in world populations to older and more needy generations continues. Today, almost 20 per cent of the world's population is over 65 and this figure is predicted to exceed 35 per cent by 2050. Robotic devices such as prostheses, exoskeletons, rehabilitation and surgical systems will enable the elderly and disabled to regain their independence as well as maintain a quality of life they had never before thought possible.
Robotic feet and legs
Rock climber Hugh Herr suffered from severe frostbite while on Mount Washington and subsequently had both his legs amputated below the knee. Now he is professor at the Media Lab (MIT) and head of the Biomechatronics Research Group, a team that studies motion science and biomechanics to develop prosthetic knees and ankle-foots. Inevitably, Herr used himself as a study case and is now the owner of a robotic ankle-foot prosthesis.
Today's prostheses are built with advanced materials, but typically only provide a passive spring response during walking. This forces the amputee to have an unnatural gait and typically expend some 30 per cent more energy on walking than a non-amputee – think of it as a bit like walking with closed ski boots. Hugh Herr's robotic prosthesis has an electric motor which replaces the muscle, while a set of springs acts as the Achilles tendon. When the foot lands, the forward-motion energy of the wearer is stored in the spring and then released together with energy coming from the electric motor in a foot push-off action. An on board computer detects and adapts to the walking behaviour and the combined system reduces fatigue, improves balance and provides amputees with a more fluid gait. A single battery charge is sufficient to walk for a complete day, which equates to about 5,000 steps. The design of the prosthetic ankle also means that the whole contraption fits inside a shoe and under trousers, so the prosthesis does its job without any noise – and nobody even notices it's there. This incredibly successful replacement limb is now in the process of being commercially developed.
Herr also has another prosthesis, this time for his knee. The Rheo Knee from Ossur, consists of two magnetic plates separated by a magnetorheological fluid (MRF). This is made up of nanoscale iron particles suspended in a carrier fluid. A magnetic field across the MRF is created by an electric current crossing the plates, causing the iron particles to form chains. This increases the viscosity and in turn increases the resistance of the joint. A computer measures the load and angle to make the joint stiff during the stance phase to support weight and to allow for a smooth leg swing by making the joint compliant. It adapts to the walking style and environment, and is constantly learning to better itself.
Even more intuitive control mechanisms are being developed, with prostheses being built that are controlled by thought processes alone. It's sufficient to only think about the job, as we would do naturally for our arms and hands, and so the robot is controlled. For this, the computer must tap the neural information from the brain or the nerves with several non-invasive and invasive techniques currently in existence. One non-invasive technique involves electrodes placed onto the skin above the muscle (electromyography – EMG) or on the scalp (electroencephalography – EEG), where in the latter the electrodes are usually fitted in a cap.
Jesse Sullivan lost both arms after accidentally touching a cable that contained 7,000V. A surgical operation rerouted the nerves that once controlled his arms through to muscles in his chest. Electrodes placed on the skin above these muscles now detect his desired motion and a computer converts the data to enact the actions of his bionic arm. So an electrical signal is sent to the hand to contract the muscle whenever Jesse wants to move the limb. The brain doesn't know the hand is gone, so the action seems perfectly natural when the signal contracts the muscle on his chest, which is subsequently picked up by the electrodes. The computer then receives the signal and thus opens the robotic hand.
Patients with motor disability sometimes have difficulty using a conventional electric wheelchair, often due to a pathological tremor. Developed by an international group with Etienne Burdet of the Imperial College in London, the Brain Controlled Wheelchair uses a screen with different buttons representing goals. A cap with electrodes is placed on the head of the user to detect the brain activity, which is used to derive the desired action, while sensors on the robot guide it to the desired goal.
Invasive methods involve needles or some form of electrical equipment placed directly inside the body. This allows the measurement of more localised signals, which can also provide for a more granular rate of control. In an experiment performed by the Duke University Medical Centre, an array of 96 hair-thin electrodes was placed in a monkey's brain. The monkey was then trained to use a joystick to position a cursor over a target on a computer screen. In the meantime, the brain activity was recorded and analysed by a computer to predict the motion of the cursor. When the researchers understood the signals they were able to control a robotic arm in the same way that the monkeys' arm was being controlled. The cursor was also now controlled by the brain signals instead of needing joystick control. At one point the monkey realised she did not need to move her arm at all and so, keeping her arm still, she controlled the robot arm using only her brain and visual feedback.
Matthew Nagle became one of the first people to use such a brain-computer interface to restore functionality lost due to paralysis. The electrodes were placed in the motor cortex that controlled his dominant left hand and arm. Although he was paralysed from the neck down, he was able to control a computer cursor and open and close an external prosthetic hand.
The goal of robotic suits is to wield very large forces without the need for using joysticks, while also allowing the user to move freely without feeling any hindrance from the exoskeleton surrounding him. This field of development has existed for some time – in the 1960s engineers built an exoskeleton called Hardiman, but such efforts soon encountered the technological limitations of the times. Computers were too slow to control the actuators in response to the wearer's movements, and the batteries and motors were too heavy.
Recent prototypes show that useable exoskeletons are now becoming a reality. Bleex2, developed by the University of California, enables a person to walk and run while carrying a heavy backpack (45Kg at 7,2Km/h). The project's goal is to help soldiers in carrying more weapons and supplies on the battlefield without sacrificing agility. The Sarcos exoskeleton is probably the strongest ever built; in a recent demonstration, a user picked up 84Kg without feeling any force from the payload on their own body. The Sarcos has an onboard combustion engine to deliver the necessary hydraulic power to the joints.
The Japanese company Cyberdyne has more civilian applications in mind, such as nurses helping patients out of their beds or even helping the elderly to walk around. Its Hybrid Assistive Limb project has a HAL-5 soon to be commercially available, costing around $1,000 per month. The device is powered by electrical motors with the computers and batteries packed into small pouches attached to the belt. With the batteries fully charged, the complete robot can be enabled for over 2.5 hours and, of course, the machine doesn't tire the way humans do. While wearing this robotic suit, an adult is able to hold up to 80Kg in weight – nearly double what he can do without it – and they can also perform a leg press of up to 180Kg.
The control architecture consists of two units. The first one measures the electromyogram (EMG) signals on the wearer's muscles; these are the signals that command the muscles to contract and generate force, and are used by the robot to move in a similar way. The second unit tunes the motion of the device so that the robot moves smoothly together with the wearer. The first time the user wears the exoskeleton, the gait, which is different from person to person, is monitored, recorded and then stored. In future uses, HAL-5 then recognizes the movement and regenerates the adjusted pattern.
Robots in the operating theatre
While robots may not be performing the surgical operations, they are certainly finding their way into the operating rooms of our hospitals. Robotic surgery today is used as an assistance to the surgeon in expanding the surgeon's capabilities – the advantages are those of amazing precision and the ability to work on an incredibly miniaturised level. The most well known system is the da Vinci Surgical System, consisting of three components: a surgeon's console, a patient-side robotic cart with robotic arms and a high-definition 3D vision system. This sophisticated robotic platform has four arms, which are introduced into the body through small incisions. Here the first advantage shows up.Traditional surgery requires large cuts to plainly observe and manipulate the surgical field which in turn increases the risk of infections and also extends recovery times. On three of the arms the instruments are mounted and the fourth arm contains the high-definition 3D vision system.
The surgeon sits away from the patient on a console and sees a magnified, high-resolution 3D image of the surgical area with a real-time progression of the instruments as he operates. The patient and surgeon need not even be in the same room; in fact some thousands of kilometres can be between them. This has led to interest from the American army who have imagined a scenario where a doctor is sitting safely away in a remote location while also able to provide immediate medical care to an injured soldier. Unfortunately, the robot cannot currently be programmed to make its own decisions so the surgeon has to manipulate handles to control the device. These movements are scaled into micro-movements of the instruments and hand tremor is filtered out, while the third arm can be used for additional tasks.
While the device is being operated, several safety checks are performed and regions of the body can be selected where the robot cannot enter so as to protect vital parts; this includes preventing the surgeon from accidentally slipping. A wide range of instruments can be attached to the three arms, such as scissors, graspers, scalpels and other specialised instruments. The system's dexterity is modelled after the human wrist, but with a greater degree of movement, and the handles also provide force feedback from the instruments so the surgeon receives tactile sensation if he is cutting through soft tissue or hard bones. Using the robotic devices, surgeons can perform even the most complex and delicate procedures with unmatched precision. This robot is currently used globally, but the very high price tag prohibits its wide adoption at present.
Researchers are clearly developing very intriguing robots and all of the current medical robots have a direct focus on helping people perform actions. While most of the robots are still in the prototype stages, we are set to see a much larger collaboration of intimate robotic use for serving the needs of humans. As a consequence of such intimate use, safety is of course a primary concern. Regardless, it's clear that medical robotics is a rapidly emerging technology and that the robots we will soon see around us will be used to enhance human mobility, strength and precision.