Akihiko Yabuki

High-speed force controller for SCARA robots

The SCARA (selective compliance assembly robot arm) robot has horizontal compliance. However, the amount and direction of compliance must be controlled before the robot can be used in actual applications. The authors have developed an active compliance controller that uses force sensors on the wrists of the robot to determine the contact forces acting on the end effector. The sensors feed this information to the trajectory generator of the robot controller. The controller achieves high-speed control (the sampling time is 1 ms) by performing all control operations in parallel using two MB8764 digital signal processors. The stability of the control was analyzed for joints having an arm that is not rigid. The force control can be stabilized by keeping the force feedback gain reasonably small.<<ETX>>

Precise microinjection into living cells by summation of fluorescence intensity

It is difficult to introduce a specific amount of a substance into cells by existing injection methods because there is no appropriate method of directly measuring the quantity of the injected substance. Although radioisotopes can be used, there is currently no apparatus that can practically handle such radioisotopes. The measurement of the diameter of a liquid droplet in air or oil is affected by surface tension if the liquid droplet is very small; but this issue does not occur with microinjection, in which a water solution is discharged under pressure through a capillary and into a cell. It is also difficult to measure the density or mass of the injected substance because of the low discharge rate, unlike the case of inkjet printers. To solve these problems, we propose a method of precise microinjection by summation of fluorescence intensity. In addition, we developed a new pressure pulse injection device that generates pressure with a rectangular waveform and a precise amplitude and pulse width to improve controllability of the discharge amount. Lastly, when the above device and method are combined, the coefficient of correlation between the specified number of pressure pulses per unit of time and the actual discharge amount exceeded 0.999. This research paper describes in detail the measurement system, standalone performance, and quantities of substances introduced into living cells.

Optical pickup adjustment system using a passive alignment method

The optical pickup of a magneto-optical drive is constructed of millimeter-size optical components, including a laser diode (LD), a collimating lens (CL), a polarizing beam splitter, some kinds of prisms, and photo detectors (PD). Each component must be assembled with micrometer-order accuracy. In particular, the astigmatism, which is adjusted by changing the position of the CL, must be within 0.65 micrometers in the optical axis direction. To enable the CL position to be adjusted quantitatively, we developed an adjustment method that uses passive alignment. We estimated the astigmatism by analyzing an image of the LD, which is acquired through the CL by illuminating the LD with the polarized light. We developed an optical-pickup adjustment system using the proposed method and tested its effectiveness experimentally. The results showed that this system can be used to adjust the accuracy to within 0.65 micrometers. Because the image of the LD and the PD are acquired clearly by this system, it should be useful for not only adjusting the optical pickup but also for visually inspecting the LD and PD.