Abstract: A rotary encoder comprises a light emitting device, a photosensor, sampling means arranged between the light emitting device and the photosensor for intercepting the light emitted by the light emitting device as the sampling means is rotated, monitoring means arranged on a side of the sampling means facing the light emitting device in adjacent to the light emitting device for sensing a portion of the light from the light emitting device and producing a signal representing a light intensity sensed, and control means for controlling the light intensity of the light emitting device in accordance with the output of the monitoring means.

Abstract: A linear motor comprises a stator of a magnetic material, a movable element of a magnetic material movable along the stator and support means for supporting the movable element to hold a magnetic force of attraction to the stator. The movable element is arranged at a position displaced from the stator in a normal direction to a direction of movement of the movable means.

Abstract: A process for purifying urokinase by contacting a crude urokinase-containing solution with a strongly acidic cation exchanger having sulfonic acid groups and adjusted to the NH.sub.4.sup.+ type to adsorb urokinase on said cation exchanger and then eluting urokinase from said exchanger, characterized in that urea is previously added to the crude urokinase-containing solution in such a rate that the final molar concentration of urea in the solution is 3 to 8 M. This process is capable of providing purified urokinase having substantially constant and high specific activity from a crude urokinase-containing solution with a high recovery regardless of purity of the crude urokinase.

Abstract: A process for purifying urokinase which comprises contacting a crude aqueous solution of urokinase with an ionic pullulan gel and thereafter separating and recovering an aqueous solution of urokinase devoid of harmful impurities.