|Centre for Automation and Robotics :: CSIC - UPM|
manipulation of high loads is a frequent task, especially in SMEs, where this
activity produces a large number of accidents and low-back disorders in
operators. According to the European Agency for Safety
and Health at Work (http://ew2006.osha.europa.eu/) about
30% of the European workers suffer from back diseases caused by physical
demands in lifting and manipulating high loads, repetitive movements and
awkward postures. As a consequence, the EU labour regulation is decreasing
the maximum load a worker is allowed to handle. The naval industry, for
instance, already limits that maximum load to
There exist some assist devices (ADs) in the market to help operator in handling loads that relieve that inconvenience, which are based on load balancers, rotation devices and/or active gravity compensators (http://www.indevagroup.com/) along with passive elements actuated directly with the operator’s force; the resultant system is safe for the operator, however, some applications require rapid and accurate motions and those devices are low, difficult to coordinate and inaccurate.
A possible solution, with a large activity in U.S.A. and a lower activity in Japan and Europe, consists of putting together the advantages of traditional robot manipulators and the advantages of the safe passive assist devices. The result is a new system named Intelligent Assist Devices (IADs).
The main aim in this project is the research in IADs and the study of their application to industry; we intent to configure and develop a system for a broad field of applications. This device will be an experimental test-bed for research in new systems, algorithms and control techniques that help in introducing these new devices in the national and European industry.
DIAM is a Spanish Acronym of “Dispositivos Inteligentes para Ayuda a la Manipulación”
The technical and scientific aims of this development are to carry out research into systems for human augmentation devices or power-assist devices, PADs, which will involve the design and development of an intelligent device to assist the handling of heavy loads of up to 75 kg with an accuracy of ±3 mm and an arm length of about 2 meters. The basic objectives are to guarantee precision placing and guidance in the face of any kind of contingency, while complying with the regulations governing operative safety, in a wide range of applications including the automotive industry, the assembly of heavy and/or bulky pieces, handling in the food industry, moving patients in the health sector, rehabilitation, etc.
The specific scientific and technical aims of this work are as follows:
The design and manufacturing of a new mechanical structure for a power-assist device capable of covering a large number of applications.
The appropriate use of sensors on the power-assist device to allow cognitive, haptic and kinesthetic interaction with the operator and his/her surroundings.
The implementation of a distributed control system that allows for data to be received from the sensors and provides the relevant coordination of the control to allow the power-assist device to interact with an operator and real/virtual environment with high stability and rendering performances.
The design and implementation of a multifunctional human-machine interface that allows the device to be handled and guided both intuitively and safely.
The design of algorithms allowing safe, stable and transparent haptic control of interaction of high-force device and human.
Fig. 1. Sketch of the main structure and dimensions of the power assists device (Units in meters).
The design of a supervision and control architecture for the definition, correction and implementation of virtual surfaces and volumes (pipes, funnels) that will assist and oversee the guidance and control of the system by the operator, offering precision and reliability for the application and safety for the operator.
We believe this power-assist device with advanced controls will be sufficiently versatile and safe to interact directly, through physical contact, with an operator and the real/virtual environment.
The mechanical structure of our Power Assists Device is defined by its three main features: workspace, payload, and operator interaction.
The manipulator must exhibit an arm extension of about 2 m; therefore, its workspace could be a two-meter-radius cylinder. The requirement about the capability of human-machine interaction fulfilling with governing laws (ergonomic and safety) recommends to fixed the workspace height between 0.25 m and 1.5 m over the ground (see Figure 1 for manipulator workspace dimensions and shape).
The heavy payload the manipulator must handled (about 75 Kg), along with the large dimensions of its workspace (two-meter radius), is the most demanding feature. To decrease static joint torques, the use of a Cartesian or SCARA mechanical structure is the normal consideration. It is well known, that in these configurations the own structure supports the payload without applying joint torques. Additionally, the SCARA structure is ordinarily faster and easier to build, thus, it has been considered as the most adequate structure for our purposes.
The SCARA structure provides, basically, two horizontal degrees of freedom (DoF). The main arm structure should provide at least three DoF –a wrist would provide up to three additional DoF– therefore, we still need to provide a vertical motion of the load. There are different possible configurations to provide the vertical motion in a SCARA structure. The most ordinary solution consists in using a vertical, prismatic joint in either the first joint or in the third joint. The last configuration is the typical one used in SCARA industrial manipulators to carry light payload. The former is used in industrial and service SCARA manipulators to handle heavy loads. Technically speaking, this is an easy solution; however, the main SCARA links move inside the workspace where the operator is also moving and to avoid dangerous situations for the operator the SCARA links are placed overhead the operator (see Fig.1 ).
This configuration can still be used as a vertical, prismatic joint, but the solution presents a very big encumbrance. One simple and efficient solution used by many industrial assist devices relies on a parallelogram structure powered through a rotary joint (see Fig. 2). This configuration is very easy to implement but exhibit a very hard shortcoming: if it is used as the first manipulator joint, then it must exert a very large torque to drive the payload plus the actuator masses of the rest of the joints.
Fig. 2. Typical use of the parallelogram structure
One new solution, which is the main contribution of this paper, is to use a parallelogram structure as the third joint as indicated in Fig. 1. In this way, joint 3 must exert a torque to move the payload plus the wrist actuator mass. The mass of the actuator 2 is directly supported by the SCARA structure. This solution gives the same workspace than traditional solution as well as same speed and accelerations but using just haft the power that other configurations. Figure 3 illustrates the final structure designed taking into account the manipulator dimensions given in Fig. 1.
Fig. 3 DIAM (a) Design; (b) Prototype
The manipulation system is intended to share its workspace with a human operator (see Figs. 2 and 3). Therefore, safety and health regulation must be fulfilled. Manipulator sub-structure that move horizontally does not interact with the operator. The lowest interacting manipulator point is 1.9 m over the ground (Point in Fig. 1). The vertical sub-structure is a small diameter rod that interacts with the operator in horizontal motions. This interaction is at a minimum because the vertical sub-structure moves with the operator, who handles the manipulator to move it to the required point.
The basic control interface relies on a force/torque sensor of 6 components (See Fig. 5) and a data glove that measures the glove position and the force exerted against the payload (See Fig. 5)
Fig. 4. Wrist and Operator-machine interface
Fig 5. Data Glove for Human-Machine interface
The controller is based on a PCI-bus computer running the QNX operating system that provides multitasking, real time features.
The actuators are AC motors controlled directly by AC drivers. This drives are commanded by commercial 3-axis PID controlling boards. An industrial PCI-bus based computer co-ordinates all I/O boards and controllers and also communicates with the operator interface. This interface allows the operator to start/stop the system and to define several operating modes (See Fig. 6).
Fig. 6. DIAM controller
P. Gonzalez de Santos, J. Estremera, E. Garcia and M. Armada, “Power assist devices for installing plaster panels in construction”, Automation in Construction, Vol. 17, pp. 459-466, 2008. PDF
P. Gonzalez de Santos, E. Garcia, J. F. Sarria, R. Ponticelli and J. Reviejo, “A new manipulator structure for power-assist devices”. Industrial Robot. To appear: online publication by Mid of May, paper publication on August 27th. 2010. PDF
J. No and P. Gonzalez de Santos, “Robot technology to support workplace ergonomic adaptation”, 40th Proceedings of the International Symposium on Robotics (ISR-2009), pp: 345 – 349, Barcelona, 10-13 March, 2009. PDF
P. Gonzalez de Santos, E. Garcia, J. F. Sarria, R. Ponticelli and J. Reviejo, “A power assists device for handling heavy loads”, Proceedings of the International Symposium on Robotics (ISR-2009), pp: 195 – 200, Barcelona, 10-13 March, 2009. PDF
L. Paredes-Madrid, P. Torruella, P. Solaeche, I. Galiana and P. Gonzalez de Santos, “Accurate modeling of low-cost piezoresistive force sensors for haptic interfaces”, IEEE The International Conference on Robotics and Automation (ICRA-2010), Anchorage, Alaska, May 3 – 8, 2010. PDF
L. Paredes-Madrid, L. Emmi and P. Gonzalez de Santos, “Improving the performance of piezoresistive force sensors by modeling sensor capacitance”, IEEE International Symposium on Industrial Electronics, Bari, Italy, 4 – 7 July, 2010. PDF
L. Paredes-Madrid y P. González de Santos, “Sistema de interacción persona-manipulador mediante guantes de datos, Interacción persona-robot”, Páginas: 129-146, Editorial Universidad Nacional de Educación a Distancia, 2009, ISBN: 978-84-692-5987-0. PDF
P. González de santos, J. Sarria, E. García, R. Ponticelli and m. A. Armada, “Brazo manipulador de cargas con pares de actuación reducidos”, No. de solicitud: P200803462. Fecha de prioridad: 5-12-2008, País de prioridad: España, Entidad titular: CSIC. PFD
L. Paredes-Madrid y P. González de Santos, “Sistema y procedimiento de control para manipuladores”, No. de solicitud: P200930173. Fecha de prioridad: 14 mayo 2009, País de prioridad: España, Entidad titular: CSIC. PDF
Video N. 1 :: DIAM preliminar arm motion
Video N. 2