Cécile Pacoret

Invited Article: A review of haptic optical tweezers for an interactive microworld exploration

This paper is the first review of haptic optical tweezers, a new technique which associates force feedback teleoperation with optical tweezers. This technique allows users to explore the microworld by sensing and exerting picoNewton-scale forces with trapped microspheres. Haptic optical tweezers also allow improved dexterity of micromanipulation and micro-assembly. One of the challenges of this technique is to sense and magnify picoNewton-scale forces by a factor of 10(12) to enable human operators to perceive interactions that they have never experienced before, such as adhesion phenomena, extremely low inertia, and high frequency dynamics of extremely small objects. The design of optical tweezers for high quality haptic feedback is challenging, given the requirements for very high sensitivity and dynamic stability. The concept, design process, and specification of optical tweezers reviewed here are focused on those intended for haptic teleoperation. In this paper, two new specific designs as well as the current state-of-the-art are presented. Moreover, the remaining important issues are identified for further developments. The initial results obtained are promising and demonstrate that optical tweezers have a significant potential for haptic exploration of the microworld. Haptic optical tweezers will become an invaluable tool for force feedback micromanipulation of biological samples and nano- and micro-assembly parts.

Non-contact mesoscale manipulation using laser induced convection flows

Laser induced convection flows is a new and promising method to achieve better manipulation of mesoscale objects (above 1 mum and below 500 mum) in a liquid medium. The temperature gradient created by laser absorption generates natural and thermocapillary (or Marangoni) convection flows. These flows are used to perform the manipulation itself. In this paper, we demonstrate for the first time that large and heavy particles can be dragged using the Marangoni convection flows. Experiments based on these phenomena show that fast and accurate underwater micromanipulation of particles up to 280 mum is possible using only a convergent 1480 nm laser beam.

2D high speed force feedback teleoperation of optical tweezers

The optical trap is a powerful non-contact approach for manipulating micron sized objects. Teleoperation of optical tweezers can be performed by coupling with a haptic interface, which allows an efficient robotic device to control positions and get force feedback. This provides users direct and intuitive microscopic interactions. The major difficulty in order for haptic devices to generate a reliable tactile sensation lies in its high frequency requirement of more than 1 kHz. This paper presents a fast force feedback teleoperation system for optical tweezers that attains this high frequency. The used force sensor is a novel event-based camera that transmits output as a continuous stream of asynchronous temporal events thus enabling high speed event-based visual processing. This new sensor is compared to a conventional frame based one to show advantages of our setup. A complex task of exploiting three dimensional target surface is performed demonstrating the robustness and efficiency of the presented method. This is the first time microspheres are used to touch targets of arbitrary form and color, which may interest broad-reaching biological and physical applications.

First high speed simultaneous force feedback for multi-trap optical tweezers

Optical tweezers use a tightly focused laser beam to trap dielectric micro-object. Haptic optical tweezers integrate a robotic haptic device into the system to control trap positions and in the meantime feedback forces. This technique opens a broad reaching applications by providing direct and intuitive interactions during micromanipulation. However, 1 kHz sampling rate is required to ensure a reliable tactile sensation. A system satisfying this requirement has been presented in our previous work. This paper goes one big step further to perform real-time high speed haptic feedback on multi-trap optical tweezers. The goal of the system is to enable users to touch the microscale object the same way as using their fingers. The used force sensor is a novel event-based vision sensor that transmits output as a stream of asynchronous timestamped events that eliminates internally the redundant static information. The associated event based algorithm can thus be able to track the positions of two spheres up to 1 kHz. A contact experiment is performed demonstrating the feasibility and the efficiency of the presented method. To our knowledge, this is the first time high speed haptic feedback is performed on multiple microspheres simultaneously in a contact scenario.

Haptic feedback of piconewton interactions with optical tweezers

Haptic feedback for micro- and nanomanipulation is a research area of growing importance with many potential applications in micro- and biotechnology. Past research often involves the coupling of atomic force microscopes to haptic devices, but the results are not satisfactory.We propose to adopt a different approach, which consists of contactless manipulation, in particular by using optical tweezers, coupled with a haptic feedback device. In this article, we describe the potential of such a tool and show with some first experiments of stable interactions between micro-particles.

High-Speed Camera Particle Tracking and Force Measurement, with Real-Time Haptic Feedback

Modern cameras can provide real-time position and force measurement of multiple trapped particles at several kHz. We investigate the accuracy and stability of this method and use it to implement a force-feedback interface.

Dual Stage Options for Interface Designs Suitable for Haptic Interaction at the Micro-Nano Scales

Direct, manual interaction with the micro/nano scales is not straightforward because the objects at this scale obey unituitive physics. For instance, in ambient conditions at the micro-scale, capillary forces dominate over many other forces. When the scale becomes smaller, Brownian motion becomes pervasive. Haptic interfaces give us the option to bring the experience of this physics with the direct reach of the human sensorimotor capabilities. To cope with the limitations of conventional force feedback devices, we present here two alternative dual-stage designs suitable to address the needs of the interaction with the micro/nano scales. The first one features very low apparent inertia, a large dynamics range and a wide bandwidth. This properties are obtained by coupling a large actuator to a small one via a viscous coupler. Feedback can then be used to achieve nearly perfect transparency. The second is a conventional force feedback device augmented with a tactile transducer. The two channels are frequency compensated to achieved a flat response from DC to 1 kHz.

Optical tweezers with 3D high speed force feedback

Optical tweezers are one of the most versatile technique to achieve biological micromanipulation. It will benefit of automatization or teleoperation for faster achieving complex tasks. Here a new vision technique is presented with high potential for high-speed, high-resolution 3D tracking of trapped objects. The characterization of this event-based biomimetic vision is fully detailed, and the performance achieves 2kHz real-time closed loop system with a potential of improvement at 30kHz sampling rate. The working range meets fully optical tweezers requirements, and the resolution is suboptical less than 40nm in the three dimensions. By using an algorithm with shape recognition, the tracking is robust to environmental conditions of real biological samples.

Haptic Feedback in Teleoperation in Micro- and Nanoworlds

Robotic systems have been developed to handle very small objects, but their use remains complex and necessitates long-duration training. Simulators, such as molecular simulators, can provide access to large amounts of raw data, but only highly trained users can interpret the results of such systems. Haptic feedback in teleoperation, which provides force feedback to an operator, appears to be a promising solution for interaction with such systems, as it allows intuitiveness and flexibility. However, several issues arise while implementing teleoperation schemes at the micro- and nanoscale, owing to complex force fields that must be transmitted to users and scaling differences between the haptic device and the manipulated objects. Major advances in such technology have been made in recent years. In this chapter, we review the main systems in this area and highlight how some fundamental issues in teleoperation for microand nanoscale applications have been addressed. We consider three types of teleoperation, including (a) direct (manipulation of real objects), (b) virtual (use of simulators), and (c) augmented (combining real robotic systems and simulators). Remaining issues that must be addressed for further advances in teleoperation for micro- and nanoworlds are also discussed, including (a) comprehension of phenomena that dictate very small object (<500 micrometers) behavior and (b) design of intuitive 3-D manipulation systems. Design guidelines to realize an intuitive haptic feedback teleoperation system at the micro- and nanoscale level are proposed.

Sensing interactions in the microworld with optical tweezers

Optical Tweezers have become a widespread tool in Cell Biology, microengineering and other fields requiring delicate micromanipulation. But for those sensitive tasks, it remains difficult to handle objects without damaging them. As the precision in position and force measurement increase, the richness of information cannot be fully exploited with simple interfaces such as a mouse or a common joystick. For this reason, we propose a haptic force-feedback optical tweezer command and a force-feedback system controlled by one hand. The system combines accurate force measurement using a fast camera and the coupling of these measured forces with a human operator. The overall transparency allows even the feeling of the Brownian motion.