JPH02279254A - Temperature compensation device for tool position in machine tool - Google Patents

Abstract

PURPOSE:To eliminate a preparatory time due to warm-up operation so as to shorten the process time by providing such an arrangement that the position of a tool during warm-up operation is stored as a time function which is then multiplied with a coefficient and is then added to a constant positional instruction signal for a thrust magnetic bearing. CONSTITUTION:There are provided a memory device 9 which stores therein a position of a tool as a time function during warm-up operation and a computing circuit 10 which multiplies the time function with a coefficient and then adds it to a constant positional instruction signal, and a positional instruction signal which varies with the time is delivered. With this arrangement, since the compensation is made in such a way that the position of the tool during warm-up operation, which is stored in memory as a time function is multiplied by a coefficient and is added to the positional instruction signal, the position of the tool may be maintained to be constant even during warm-up operation. As a result, a preparatory time due to warm-up operation is eliminated so as to shorten the processing time and to reduce the operating cost.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of controlling a machine tool spindle using a controlled magnetic bearing having, for example, five degrees of freedom.

BACKGROUND OF THE INVENTION In recent years, machine tool main spindles that use five-degree-of-freedom controlled magnetic bearings to rotate at high speeds of around 100 rpm or higher have been put into practical use. The 5-degree-of-freedom control J-type magnetic bearing used for these main shafts is composed of two radial magnetic bearings and one thrust magnetic bearing. A radial shaft bearing generally includes two sets of electromagnets for the X-axis circumference and Y-axis on an XY plane perpendicular to the axis of the main shaft, an X-axis position sensor, and a Y-axis position sensor. Each of these position sensors detects the position of the main axis in the X-axis direction and Y-axis direction, amplifies the deviation from a fixed position command signal, performs phase compensation, and then amplifies the power to determine the X-axis circumference and Y-axis circumference. It is designed to control the electromagnetic force of the electromagnet. A thrust magnetic bearing consists of two electromagnets around the Z-axis and a Z-axis position sensor, assuming that the axes of the main shaft are two axes. The electromagnetic force of the Z-axis circumferential electromagnet is controlled by detecting the position of the main shaft in the Z-axis direction with a position sensor, amplifying the deviation from a fixed position command signal, performing phase compensation, and then amplifying the power. There is.

Problems to be Solved by the Invention In conventional machine tool spindles using 5-degree-of-freedom controlled magnetic bearings as described above, when rotating at high speeds, the spindle generates heat and thermally expands due to eddy current loss in the motor and magnetic bearings. , the position of the tool attached to the spindle is in the thrust direction (axial direction)
will change significantly. Therefore, when performing sensitive machining, a warm-up operation must be performed until thermal expansion is saturated and the tool position is constant, which increases the time required for machining and increases the operational cost of warm-up operations. The problem was that it could get damaged.

Therefore, the present invention provides a temperature compensation method for the tool position in a machine tool spindle in order to solve the above-mentioned problems.

Means for Solving the Problems A thrust magnetic bearing control circuit includes a device that stores the tool position during warm-up operation as a time function, and an arithmetic circuit that multiplies the time function by a coefficient and adds it to a constant position command signal. is provided to output a position command signal that changes over time.

According to the present invention, the tool position during warm-up operation is stored as a time function, and the position command signal is added to the time function multiplied by a coefficient. Even if the tool position changes by a certain amount, a position command signal will be output that will control the tool to a position with that amount subtracted. Therefore, even during warm-up operation, the position of the tool (in the thrust direction and axial direction) is maintained at a constant position.

Embodiments Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a control circuit of a five-degree-of-freedom control type magnetic bearing in an embodiment of the present invention. FIG. 2 is a diagram showing changes in tool position over time during warm-up operation. It has been experimentally confirmed that this change in tool position is reproducible under the same machining conditions. This value is stored in the storage device 9 as a time function.

At time 0, there is no thermal expansion yet, so the position command is a constant value S, and the tool position is Z at this time. becomes. When the conversion coefficient between the position command and the tool position is a, there is a relationship of 5o=a*20. At time t, the tool position z (t) at t is read from the storage device 9, and the arithmetic circuit 10
Output to. In the arithmetic circuit 10, -z(t) multiplied by the displacement and command voltage conversion coefficient a is added to the position command signal, and the corrected position command signal s(t)=S0-a*z(t) is generated. At this time, the tool position is Z' (t)
= s (t) / a = So / a - z (i) However, since the tool position on the spindle is displaced by z (t) due to thermal expansion, the actual tool position Z (t) is controlled to a constant position Z (t) = Z' (t) + z (t) = 80/a = 26.

Effects of the Invention According to the present invention, the position command signal is corrected by adding the tool position during warm-up stored as a time function multiplied by a coefficient. The tool position remains constant. As a result, preparation time due to warm-up operation is eliminated, machining time is shortened, and operating costs are also reduced.

[Brief explanation of drawings]

Fig. 1 is a control circuit diagram of a 5-degree-of-freedom controlled magnetic bearing according to an embodiment of the present invention, Fig. 2 is a diagram showing changes in tool position over time during warm-up operation, and Fig. 3 is a conventional 5-degree-of-freedom control type magnetic bearing. FIG. 3 is a control circuit diagram of a controlled magnetic bearing. 1...Main shaft, 2a, 2b, 3a, 3b...
...Radial magnetic bearing electromagnet, 2c, 3c...
・Electromagnet for thrust magnetic bearing, 4 a r 4 b,
4 c...Position sensor, 5a, 5b, 5c...
...Power amplifier circuit, 6a. 6 b, 6 c-...phase compensation circuit, ? a, 7b
, 7c... Comparator, 8... Tool, 9.
...Time function storage device, 10...Arithmetic circuit. Name of agent: Patent attorney Shigetaka Awano and one other person

Claims (1)

[Claims] The control circuit for the thrust magnetic bearing of the main spindle of a machine tool using a controlled magnetic bearing includes a device that stores the tool position during warm-up operation as a time function, and a position command signal for the thrust magnetic bearing by multiplying the time function by a coefficient. A temperature compensation device for the tool position of a machine tool, which is equipped with an arithmetic circuit that adds to the temperature.