Graphical design develops robotics
01 January 2008
LabVIEW is used to control the robotic arm responsible for precise photodynamic therapy application for patients.
The challenge was to develop an automated robotic manipulator for performing photodynamic therapy (PDT) on cancer patients. In response, a graphical system design was used to design a robot capable of precise movement and highly accurate placement of PDT therapy.
Using LabVIEW, we get a smoother move resulting in less abrupt transitions, which both saves time and improves performance, reports members of the Faculty of Engineering, Lebanese University.
Treatment stages
When treating cancer, oncologists select from a number of techniques depending on the type and stage of the tumour in question. The most common techniques used today are photodynamic therapy (PDT), surgery, radiation therapy, chemotherapy, hormone therapy and immunotherapy.
PDT is a special form of phototherapy, a term comprising all treatments that use light to induce beneficial reactions in a patient’s body. PDT is a new technique capable of destroying unwanted tissue while sparing normal tissue.
During PDT treatment, a drug called a photosensitiser is administrated to the patient by injection. The photosensitiser alone is harmless and has no effect on either healthy or abnormal tissue. However, when light emitted by a laser is directed at the tissue containing the drug, the drug is activated and the tissue is rapidly destroyed precisely where the light has been directed. This technique allows for a focused targeting of the abnormal tissue with careful application of the light beam, which translates into more effective treatment.
Robotics
At the Lebanese University, an automated robotic mechanical manipulator was developed. Its primary function consists of skimming along the patient’s skin while performing the PDT technique. The robot moves the laser heads over the affected area of the patient’s body in certain geometrical designs, such as circular or elliptical shapes, so that the tumour can be destroyed.
Achieving a geometrical shape over a patient’s body requires five movements:
Three translations whose functions are defined as follows:
Z provides the vertical control of the treating laser heads
Two rotations
To achieve these five movements, five corresponding stepper motors must be controlled by the command signals generated by the command system and delivered by the electrical circuits to the motor drivers.
Command system
LabVIEW directly controls four stepper motors (X, Y, è, and Ö) and a Microchip Technology PICmicro microcontroller controls the fifth motor (Z). The NI PCI-7334 motion controller uses a dual-processor architecture, a CPU (central processing unit) and a DSP (digital signal processor) form the backbone of the motion controller.
At the motion driver software level, the PCI-7334 uses commands coded in LabVIEW along with configuration settings from the Measurement & Automation Explorer (MAX) as roadmaps to generate command signals to move the motors. In the MAX configuration, the clockwise/counter-clockwise pulse stepper output configuration is used; the first output produces CW pulses when moving clockwise, while the second output produces CCW pulses when moving counterclockwise.
Electrical circuits
In the head of the robot, eight optical on/off sensors detect any object that appears within 1cm in front of them to allow the distance between them and the surface right below to be revealed.
To protect the motion system from physical damage and to detect trajectory limits, each axis uses two physical limit switches, forward and reverse. All the sensors, limit switches and motor drivers are connected directly to the PCI-7334 through an NI UMI-7764 motion interface that enables pin-level connectivity.
The motor drivers and limit switches of the X, Y, è, and Ö axes are connected to the four motion I/O terminal blocks of the UMI-7764. In order to maintain a synchronous move of the five axes, the first and third UMI-7764 breakpoints are connected as inputs for the microcontroller that loads the fifth (Z axis) motor. Four of the sensors are connected to the analogue input terminal block of the UMI-7764; the others are connected to the trigger/breakpoint terminal block. A joystick makes the system more user-friendly. At any time, the parameters can be modified, the system can be halted, and the position of the head can be adjusted. An SH68-C68-S cable connects the motion controller to the UMI-7764.
Software development
Initially, the software was developed by simplifying the robot configuration into 2D applications and by simulating movement using LabVIEW. Then the same reasoning was extrapolated to a 3D problem and the movement simulated following the same process adopted in the simple 2D application. The software that runs the real robot is the 3D simulation itself, transformed into a program that reads from real sensors and runs real motors.
The main task of these programs lies in reading the sensor’s status (on/off) first, and then in defining the movements of the robot head.
Benefits
Unlike text-based programming languages, LabVIEW uses icons instead of text lines in the creation of applications, which made software development significantly easier. Furthermore, LabVIEW contains a huge library that includes a large number of multipurpose subVIs like FlexMotion that the team have used extensively in their software.
The PCI-7334 motion controller offers the performance and determination needed to solve the most complex motion applications, performing command fulfilment, host synchronisation, I/O reaction and system supervision. As a result, the movement is smoother, with less abrupt transitions, which both saves time and improves performance.
Assad Kallassy, Georges Issa and Houssam Bitar are members of the Faculty of Engineering, Lebanese University, Second Branch. Email: (kallassy@ul.edu.lb)
Oncology
Oncology is the study of cancerous tumours; their development, diagnosis, treatment and prevention. Practitioners, or oncologists, will co-ordinate patient care in the form of physiotherapy, counselling and clinical genetics.
Oncology covers the diagnosis of cancer, its therapy whether surgery, chemo- or radiotherapy. It also includes follow up care and screening efforts to prevent incidences of cancer.
Photodynamic therapy (PDT) is a form of phototherapy, where light is used to induce reactions in the patient.
The technique can potentially destroy unwanted tissue without effecting healthy tissue. A photosensitiser drug is administered. In itself this drug, which is usually injected into targeted areas, is harmless. Light, usually a laser directed onto the tissue, activates the drug which rapidly destroys the affected tissue.
Thus, by careful application of the light beam, the technique can be targeted selectively to the abnormal tissue.
Some of the photosensitiser drugs being developed can concentrate in tumours, which also helps oncologists to target the cancer. A side-effect of the treatment is that some forms of photosensitiser drugs can result in skin photosensitivity, which means that patients must stay out of bright light for some time after the treatment.
Contact Details and Archive...
Related Articles...
Most Viewed Articles...