Catálogo de publicaciones - libros

This paper describes the study of a gripper using the surface tension effects to pick and place the 0.5mm or 0.3mm diameter balls of a millimetric watch bearing. Two liquid supply strategies have been tested (pressure drive and tip dip). The effects of the coating (through the measurement of the contact angles), the presence of an internal channel and the size of the gripper have been studied. Analytical and numerical force models have been developped and validated thanks to a test bed allowing the measurement of the developped force (typically of the order of 100 µN) with a resolution of 1 µN. A complete pick and place cycle has been performed using the 0.5mm diameter gripper. Such a test has still to be done in the future with the 0.3mm diameter gripper.

Optical micro parts, such as glass fibres, require handling and alignment accuracies down to the sub micrometer range. Addressing this task, one aim of the Fraunhofer IPT is the development of new concepts of active gripper systems. In this context a highly integrated, adaptive, rugged and economical gripper system particularly for accurate handling and alignment of flexible micro parts down to the sub-micron level has been developed. This gripper system can be used on conventional robot systems for carrying out micro-assembly operations. The robot system does the pre-positioning, the tolerances necessary for the micro-assembly are subsequently realized directly at the tip of the gripper with the gripper integrated multi-axes system. Positioning systems that achieve the required positioning increments in the sub micron range are already existent. However, the problem of such systems is that they are normally highly sensitive against mechanical impact and extremely cost intensive. In this paper the development of a highly robust gripper-integrable axes system and its integration in a novel gripper design with a multi-axis adjustment system is presented.

This paper presents the design, fabrication and characterization of a device able to exchange the tip part (so-called the tools) of a two fingered microgripper. The principle of this tool changer is based on the use of a thermal glue whose state (liquid or solid) is changed by heating or cooling. Several kinds of pairs of tools have been designed. The suitable pair of tools can be chosen according to the size, shape and material of the object to manipulate. The tool changer enables one to perform a sequence of elementary micromanipulation tasks (i.e. an assembly sequence) by using only one gripper mounted on only one manipulator. The tool changer has been automated and successfully tested in air and in the vacuum chamber of a Scanning Electron Microscope (SEM). It brings flexibility to the micromanipulation cell and contributes to reduce the costs, the used space and experimentations time for micro-manipulations in the SEM. The assembly of a ball bearing (the balls are 200 µm. in diameter) has been successfully tested using the microgripper equipped with the tool changer in a SEM. This tool changer has been designed for a microgripper but can be easily adapted to lots of other kinds of systems.

The paper describes the modeling and experimental investigation of the application issues of electrostatic based micro-gripping. The design of an electrostatic gripping system for both grip force measure and pickup and place experiment is presented. A finite element model is made to study the gripping environment and process related features. The design and validation of the model are provided. Investigation of the influences that the gripping process gives out to and may receive from the operating environment is discussed. The preliminary result shows that grounded objects that come into the gripping area do not influence the gripping action significantly. Some real gripping actions are performed. Discussions on the scope of gripping environment and process related features are raised on basis of gripping experiments and observations. The phenomena of charging and discharging on the gripper isolator may add difficulties to gripping control. The investigation is concluded in a form of Process Data Sheet. The research draws an insight view on the application criteria of electrostatic gripping technology. Both advantages of the gripping principle e.g . flexible in terms of part dimension and geometry, and restrictions of the application are illustrated.

The paper propose a new approach in order to design a generic microparts feeder. The method based on a classification scheme allows to emerge the principal characteristics of each studies solutions. The different criteria take into account the specifities of the micro world and moreover the main characteristics for the feeding functions. Thus, we analyse three systems and confront them to find the generic and flexibility aspects.

The need of fully automated microassembly systems place specific functional requirements on the design and fabrication of critical elements such as grippers, sensors, manipulators and feeders. A new microfeeder design is proposed based on contactless pneumatic distributed manipulation. By cooperation of dynamically programmable microactuators, a number of feeding functions and even some elementary assembly operations can be achieved.

The paper describes the development of a micro-parallel-SCARA robot adapted in size to MEMS products. The degree of miniaturization is optimized concerning a smaller structure but high accuracy in a workspace dimensioned to chip card size. The robot supports the mostly used four degrees of freedom with a base area of less than 150 × 150 mm^2. It is the result of a cooperative project between the Institute of Machine Tools and Production Technology at the Technical University of Braunschweig and Micromotion GmbH. This company is an innovative manufacturer of miniaturized zero-backlash gears and actors, which are used as main drives of the robot.

In the future the assembled parts become smaller and the precision demands increase in many cases. Grippers are one factor of the solution to make a competitive automation assembly system. Grippers have to be flexible and also capable of holding parts without dropping them during accelerations. Other demands for a gripper for mini and micro assembly applications are, among other things, accuracy and good force/size ratio. By using servo grippers also in high-precision applications for miniature-size parts, a noticeably amount of time will be saved. This paper presents two different kinds of developed two-fingered servo grippers with parallel moving mechanics, as well as the developed test systems for servo grippers and some test results.

In this paper the development of a macro parallel robot is presented in which conventional bearings are replaced by pseudo-elastic flexure hinges. The robot consists of a spatial parallel structure with three translational degrees of freedom and is driven by three linear direct drives. The structure has been optimized with respect to workspace and transmission ratio. Additionally, in simulations with the FEA tool ANSYS different geometrical arrangements and combinations of flexure hinges have been investigated with respect to the dynamic behavior of the compliant mechanism. Due to the symmetrical character of the structure and the optimized design of the combined flexure hinges the structure is very stiff. The experimental measured repeatability of the compliant robot is below 0.3 µrn.

This paper presents a test environment enabling the study of factors affecting on the success of a robotic precision assembly work cycle. The developed testing environment measures forces and torques occurring during the assembly, and uses a system based on machine vision to measure the repeatability of work piece positioning. The testing environment is capable of producing exactly known artificial positioning errors in four degrees-of-freedom to simulate errors in work-piece positioning accuracy. The testing environment also measures the total duration of the robot work cycle as well as the durations of all essential phases of the work cycle. The testing environment is best suited for light assembly operations and has measurement ranges of ±36 N and ±0.5 Nm and the vision system has a field-of-view mm. The latter part of this paper presents the results of the research done in order to find out how some selected factors affect the assembly forces of robotic assembly. These factors include work piece and process parameters such as work piece material and design (chamfered/straight), positioning tolerances, and robot insertion motion speed.