(1)Detailed description of factors for bias error

This section tries to deepen understanding on factors and solutions for "bias errors" taking the actual measurement equipment as an example.

・Here, fluctuating factors for "bias errors" due to temperature drift are roughly divided into two groups: a) stabilizing temperature of measurement equipment, and b) thermal deformation in the mechanical components for automation devices.
a)Temperature drift in measurement equipment
b)Thermal deformation of automation devices

・This section describes a) Temperature drift in measurement equipment.

・Measurement equipment for positioning consists of three main components: "measurement sensor", "circuit for measurement", and "mounting mechanism for measurement sensor". Accuracy variation on measurement time varies by component. Universal test machine in Fig.1 consists of "measurement sensor" (load sensor), "circuit for measurement" (measuring unit for load sensor), and "mounting mechanism for measurement sensor" (gate type mechanism).

・Although a "measurement sensor" itself is designed to be insensitive (cover protection, material selection, etc.) to fluctuations in the environment, the sensors using composite structural members, such as laser beam, piezoelectric element, etc. are likely to be affected by temperature drifts.

・In the "circuit for measurement", temperature drifts in many electronic components on the circuit board cannot be avoided because the temperature in the circuit boards, etc. inside rises to a certain degree after the power on. Handling, thus, is necessary in such a way that measurement should start after the temperature rises to certain degree. The period until the temperature reaches the required level is called "warm-up time". "Warm-up time" required for measurement equipment is generally about 10 minutes.

・"Mounting mechanism for measurement sensor" is affected by temperature changes in the mechanical components. In the testing facility where accurate measurement is required, even the universal test machine in Fig.1 is also placed under the constant room temperature.

・Fig.2 shows the relationship between temperature drift in "circuit for measurement" and the "warm-up time" as the countermeasure. The straight line in figure 2 represents the ideal measurement data. The data that has the property of curved line at the start shows the case where temperature drifts. Effects of temperature drift can be avoided by starting the measurement at the point when the "warm-up time" of this curved line is past.