When designing micro-scale tactile probes, a design trade-off must be made between the stiffness and flexibility of the probing element. The probe must be flexible enough to ensure sensitive parts are not damaged during contact, but it must be stiff enough to overcome attractive surface forces, ensure it is not excessively fragile, easily damaged or sensitive to inertial loads. To address the need for a probing element that is both flexible and stiff, a novel micro-scale tactile probe has been designed and tested that makes use of an active suspension structure. The suspension structure is used to modulate the probe stiffness as required to ensure optimal stiffness conditions for each phase of the measurement process. In this paper, a novel control system is presented that monitors and controls stiffness, allowing two probe stiffness values (“stiff” and “flexible”) to be defined and switched between. During switching, the stylus tip undergoes a displacement of approximately 18 µm, however, the control system is able ensure a consistent flexible mode tip deflection to within 12 nm in the vertical axis. The overall uncertainty for three-dimensional displacement measurements using the probing system is estimated to be 58 nm, which demonstrates the potential of this innovative variable stiffness micro-scale probe system.

Abstract:Micro-scale probing systems are used on specialist micro-coordinate measuring machines to measure small, intricate and fragile components. Probe stiffness is a critical property of micro-scale probing systems; it influences contact force, robustness, ease of manufacture, accuracy and dynamic response. Selecting the optimum stiffness, therefore, represents a significant design challenge, and often leads to undesirable compromises. For example, when contacting fragile surfaces the probe stiffness should be low to prevent damage; however, for a more robust probing system the stiffness should be increased. This paper presents a novel concept for micro-scale probing systems with the ability to quickly and easily change and control probe stiffness during use. The intended strategy for using the proposed probe is first explained. Then the new concept is fully defined and explored through a combination of finite element analysis and experimental results. Two possible configurations of probe are described, and models for predicted performance for each are presented and compared. The models demonstrate significant stiffness reduction is possible with the proposed concept, and show it is theoretically possible to achieve a probing system with perfectly isotopic stiffness.

No abstract

Citation: ALBLALAIHID, K., KINNELL, P. and LAWES, S., 2015. Fabrication and characterisation of a novel smart suspension for micro-CMM probes.Sensors and Actuators 232, Additional Information:• This paper was accepted for publication in the journal Sensors and Ac- Abstract: In tactile micro coordinate metrology, miniature probing systems are required to allow geometric measurements of miniature, delicate, high precision components. These probing systems typically comprise of a small stylus of only a few mm in length, with a spherical tip of around 100 µm in diameter or less. The stylus is mounted to a flexible suspension structure which is designed to deflect during measurement, and defines the stiffness of the probing system. Stiffness is of critical importance for optimum measurement performance, and selection of the correct stiffness involves a difficult trade-off. Stiff probes are needed to overcome surface attraction forces which are significant for the small stylus tips, while flexible probes are needed for contact with delicate parts to reduce contact stress and ensure no damage is caused. To eliminate the need for compromise a novel micro tactile probing system with active stiffness control using a novel suspension structure has been designed. This paper presents the initial fabrication and the test of the suspension structure. The stiffness of the structure is assessed by measuring the modal frequencies of the suspension structure that correspond to vertical and lateral probe motion. Using this method results show it is possible to reduce the vertical and torsional frequency by 69% and 33 %, respectively. Using finite element analysis it is shown that this equates to vertical and lateral stiffness reductions to 12% and 46% of their initial value respectively.

This paper presents a simple fabrication process that allows for isolated metal tracks to be easily defined on the surface of 3D printed micro-scale polymer components. The process makes use of a standard low cost conformal sputter coating system to quickly deposit thin film metal layers on to the surface of 3D printed polymer micro parts. The key novelty lies in the inclusion of inbuilt masking features, on the surface of the polymer parts, to ensure that the conformal metal layer can be effectively broken to create electrically isolated metal features. The presented process is extremely flexible, and it is envisaged that it may be applied to a wide range of sensor and actuator applications. To demonstrate the process a polymer micro-scale gripper with an inbuilt thermal actuator is designed and fabricated. In this work the design methodology for creating the micro-gripper is presented, illustrating how the rapid and flexible manufacturing process allows for fast cycle time design iterations to be performed. In addition the compatibility of this approach with traditional design and analysis techniques such as basic finite element simulation is also demonstrated with simulation results in reasonable agreement with experimental performance data for the micro-gripper.