Such sensors as described above are used in particular in injection moulding and are therefore exposed to high pressure and temperature differences. An example of a sensor according to the prior art is the sensor type 6167 from Kistler Instruments AG in Switzerland, also described in U.S. Pat. No. 6,212,963, which is hereby incorporated herein for all purposes by this reference. Typically such sensors have a relatively thick diaphragm, because in use they are exposed to severe mechanical stress, for example when removing the injection moulded part.
For technical reasons, pressure sensors for other application areas can often not be used as pressure sensors in cavities in injection moulding, since they have, for example, too slow a response time or too low a resolution, are not sufficiently temperature-resistant, or in particular also, they cannot withstand the constant high temperature changes.
Such pressure sensors are always mounted in the tool with a small spacing gap. In injection moulding with low-viscosity materials, this moulding material ultimately flows into the gap between sensor and tool and thereby causes a lateral pressure on the frontal region of the sensor. This pressure, acting radially on the sensor housing, ultimately causes a deflection of the diaphragm, which generates an error signal. Studies using comparative measurements, in which a reference measurement was carried out with a thin film glued to the front face, have produced a deviation of up to 20%.
Further problems with such sensors are caused by stresses of the fronts of the sensors when the mounting conditions are correspondingly unfavourable. It has been shown that pressure sensors in the injection moulding field, due to their high-resolution property, tend to generate an error signal on the measuring element even under very small stresses of the housing.
USPTO Backgrounds
USPTO Backgrounds