MICRO-MOTION SYSTEMS Micro-robots and micro-conveyers realized by Polyimide Joint Actuators
Researchers Thorbjörn Ebefors Johan Ulfstedt Mattsson Edvard Kälvesten Göran Stemme	Sponsors Swedish Research Council for Engineering Sciences (TFR) Swedish Foundation for Strategic Research (SSF).
We have recently developed a new robust polyimide micro joint useful both for dynamic (e.g. actuator) and static (e.g. 3D sensor) applications. As spin-off projects from the polyimide joint research different micro-motion systems has been developed using arrays of movable robust silicon legs. The motion is achieved by thermal actuation of polyimide joint actuators using electrical heating.
Micro-conveyers Micro motion system (e.g. conveyance system or micro-robot) based on arrays on movable robust silicon legs raised using polyimide micro-joints has been developed and investigated. The motion, illustrated in the figure to the right, is obtained by asynchronous actuation of the polyimide joints using electrical heating. Successful experiments of moving objects in the mm range have been performed with a one-dimensional test conveyor. The maximum measured velocity was 12 mm/s for a system consisting of legs with a length of 0.5 mm at a driving frequency of 250 Hz. Different loads were applied on a test conveyor with 12 legs. As shown in the figure below, the weight of the heaviest mass that was moved was 2 g (or 350 mg / leg). Figure: The principle used to realize 1-D micro-motion systems (both micro-conveyers and micro-robots). By the use of asynchronous driving where at least two spatially separated groups of actuators are turned on and off at different times, holding and driving the object alternately, a smooth and effective movements is achieved. A displacement equal to 2·x is obtained during one period . A 180 degrees phase-shift between x+ and x- will result in displacement in the opposite direction.
Figure: The fabricated micro-conveyer with twelve Si legs each 500 µm longs and with four V-grooves in the polyimide joints. To the left different versions of conveyers are shown . To the right one of the microconveyers is shown during a load test. The 2 g weight, which can be moved by actuation of the polyimide joints, corresponds to 350 mg on each of 30 µm thick silicon legs.
Micro-robots The same chips that was used for the micro-conveyer test were wire-bonded with long (>10 cm) gold wires and turn up side down to obtained a walking micro-robot. The characteristics for the micro-robot is summarized bellow.
Figure: The principle for the micro-robot leg movements using robust polyimide joint actuators.

Characteristics of the fabricated micro-robot.

Materials Legs Micro-joint Heating resistor	bulk silicon polyimide (HTR-3 200 from OCG) p++ polysilicon (boron-ion implanted)
Dimensions Chip size Leg Number of legs          ver. 1+2 :                                    ver. 3+4:	15 x 5 x 1.5 [mm3]15 x 5 x 1.5 [mm3] 500 or 1000 x 600 x 30 [µm3] 2 sets of legs ( and ) with 4 or 6 legs in each 4 sets of legs (, , and ) with 2 or 3 legs in each
Measurements Maximum stroke length Maximum walking velocity Maximum load Life-time	170 resp 340 [µm] for 0.5 and 1 mm long leg (@ low frequency) 5 [mm/s] (@ 250 Hz and 200 mW/leg) > 2.5 gram (still walking) > 200.000.000 (steps)

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