Determining the zero point of the water ring: To achieve precise reciprocating control, a unique starting reference point for the honing process—the zero point of the water ring—must be identified. This presents a challenge: how to ensure that the zero point of the water ring remains unique and constant. Since the sensing signal of the contactless proximity switch is transmitted within a certain area, if the sensing block is anywhere within the signal range of the contactless proximity switch at the moment the machine is powered on, the CPU will read the value of the zero point of the water ring. This value will not be a fixed point in space; the difference could be as much as tens of millimeters, making it impossible to uniquely determine the position of the water ring and thus impossible to achieve accurate control.

If, at the moment the machine tool is powered on, the sensing block is not within the signal range of the water ring contactless switch, there are two possibilities: either the sensing block is above the water ring switch, or it is below it. For the CPU to read the value of the water ring's zero point, the sensing block must first be brought close to the signal range of the water ring switch. Therefore, there are upper and lower approximation points, which differ by several millimeters, resulting in a non-unique outcome.

If the zero point is set at the upper limit position, although the spindle cannot move further upwards to the highest point of the upper limit position when reciprocating upwards, and the spindle can only approach the upper limit position downwards when moving upwards, the spindle must be moved to the upper limit position before each power-on reciprocating cycle to start working from the upper limit position. This is both troublesome and affects work efficiency.

This approach proved ineffective and failed to achieve a breakthrough. During subsequent debugging, through careful observation and analysis, it was concluded that the spindle's stopping position at the instant the machine tool is powered on can only be one of three possibilities (see attached diagram):

(1) Stop within area A, which does not transmit signals, above the upper limit and the water ring switch;

(2) Stop within zone B, the range of the water ring switch signal;

(3) Stop in zone C below the water ring switch and do not send a signal.

In the first scenario, for the spindle to reciprocate normally, the sensing block must be within the signal range B of the water ring switch. In the second scenario, the sensing block itself is within the signal range B of the water ring switch. In the third scenario, for the spindle to reciprocate normally, it must be controlled within the reciprocating area. To achieve this control, a unique coordinate reference water ring position zero point must be established. Therefore, before reciprocating, the spindle must first reach the signal range B of the water ring switch. This categorizes the first and third scenarios into the second scenario—coordinate value zero point registration. From zero point registration until the spindle enters the reciprocating area for normal reciprocating motion, the spindle must receive a downward reciprocating command. In summary, for the spindle to enter the normal reciprocating area, there must be a process of moving downwards from the water ring switch position, from signaling to no longer signaling. We take the lower edge signal of this signaling to signal loss as the zero point registration assignment signal; this result is unique. Regardless of whether the main shaft approaches the water ring switch from above or below, we only take the moment when it leaves the water ring switch "downward" and loses signal as the benchmark. This is because we know that for the same contactless proximity switch, under the same conditions, the signal detection distance from signaling to loss of signal is constant. That is, as long as the position of the switch remains unchanged, the spatial position of the sensing block leaving the water ring switch downward and causing the switch to lose signal is constant. This successfully solves the problem that the zero point of the water ring position is unique, making it a breakthrough.

If the coordinate of the spindle at the zero point of the water ring position is set to 0, and the encoder count is positive when the spindle rotates downwards, then the count value in the reciprocating zone will be positive. However, when the spindle rises above the water ring switch position to the upper limit region, the count value will be negative, which causes inconvenience for data processing. To ensure that all data are positive, the coordinate value assigned when registering the zero point is set to 5000, i.e., 5000 × pulse equivalent = 5000 × 0.02356 = 118mm. The distance between the water ring switch and the upper limit switch of this machine tool is less than 100mm, so even if the spindle rises to the upper limit position and stops, the count result will not be negative. For example, if the zero point of the water ring switch is set to 5000, the coordinates of the upper reversing point are set to 6300, and the coordinates of the lower reversing point are set to 18000, then the distance from the upper reversing point to the water ring switch is: (6300-5000)×0.02356=30.6mm, and the distance from the lower reversing point to the water ring switch is: (18000-5000)×0.02356=306mm. The reciprocating stroke of the spindle is: (18000-6300)×0.02356=275mm. By changing the coordinate settings of the upper and lower reversing points, the size of the reciprocating stroke and the reciprocating range of the spindle can be adjusted.