Abstract: In a method for measuring ink density of printed sheets by means of photodiodes which scan light reflection from measuring marks provided on printed sheets, the start of a dynamic measuring process during the running of the printing machine is released by the control of impulse flanks, and the reflected light is scanned by sensors having a short response time. A medium reflection value of the surface of the measuring mark is determined. The control of impulse flanks takes place by a leading edge of the mark printed on the sheet, and the signal, released by that control, switches on the photodiodes and the light source. A changed voltage occurring at the output of each photodiode is amplified, and its peak value is stored; and the photodiodes and the light source are switched off thereafter.

Abstract: A densitometric head for measuring ink density of prints in a running printing machine includes a light source for transmitting light on the measured surfaces and sensors for receiving the remitted light. To simplify the construction and eliminate heat effects of the light source, the latter is arranged in one focal point of an elliptic reflector whereas the measured surfaces are situated in or close to the other focal point where an image light source is formed from the light reflected in the reflector. A heat protective filter is arranged between the two focal points to eliminate heat effects on the sensor.

Abstract: A secondarily controlled hydrostatic machine with variable volume is connected to a line with impressed system pressure which is fed by a primary unit. By switching over the primary unit the secondary unit is subjected to a displacement amount which results in as large as possible a pivot angle of the secondary unit to obtain the highest possible efficiency. The switching over takes place in dependence upon an upper and lower switching point corresponding to the desired pivot angle range of the secondary unit.

Abstract: A hydrostatic machine having a fixed displacement volume which is connected to the operating chamber of a hydraulic cylinder which machine is mechanically coupled to a second hydrostatic machine having a variable displacement volume to control the force exerted by the hydraulic cylinder. When control liquid is displaced from the working chamber of the cylinder the first machine acting as a motor drives the second machine which displaces control liquid into an accumulator. Vice versa, liquid is taken from the accumulator and the second machine acting as a motor drives the first machine which feeds liquid into the working chamber. The pressure in the working chamber, or, respectively, the force exerted by the cylinder is maintained constant by a corresponding adjustment of the displacement volume of the second machine.