ULTRA-PRECISION CUTTING QUASI-STATIC FORCE MEASUREMENT SYSTEM BASED ON PIEZOELECTRIC CERAMIC SENSOR

Abstract

The present invention relates to the field of ultra-precision cutting technology, specifically to a ultra-precision cutting quasi-static force measurement system based on piezoelectric ceramic sensor. This system includes a piezoelectric ceramic force sensing unit that responds to the force applied by a single-point diamond tool and generates an electric charge signal sent to an external post-processing module. The post-processing module includes a preamplifier circuit for the charge, a low-pass filter circuit, an ADC (Analog-to-Digital Converter) module, a DSP (Digital Signal Processor) and a computer. The computer calculates the actual force F.sub.i applied to the piezoelectric ceramic force sensor at moment i based on the solution of the dynamically changing force f.sub.i at each moment and the accumulation of the dynamically changing forces from previous moment.

Claims

1. A ultra-precision cutting quasi-static force measurement system based on piezoelectric ceramic sensor comprises: a piezoelectric ceramic force sensing unit, located at the machining end of the ultra-precision cutting system, and used for mounting the single-point diamond tool; the piezoelectric ceramic force sensing unit, when subjected to the force exerted by the single-point diamond tool, generates a charge signal that is transmitted to an external post-processing module; wherein the post-processing module comprises: a preamplifier circuit for amplifying the signals detected by the piezoelectric ceramic force sensing unit; a low-pass filter circuit for filtering the output signal from the preamplifier circuit; an ADC module for converting the voltage signal passed from the low-pass filter circuit into a corresponding digital signal; a DSP signal processor for real-time processing of the digital signal and transmitting the processed data to a computer; the computer calculates the actual force f.sub.i acting on the piezoelectric ceramic force sensor based on the dynamic variation of forces at each moment, and obtains the actual force F.sub.i acting on the piezoelectric ceramic force sensor at the moment i by accumulating the dynamic changing force at moment i; $F_i=F_{i-1}+\frac{U_i-U_{i-1}{e}^{-T/?}}{c};$ T represents the time interval between moments i and i?1; ? represents the time constant of charge leakage decay; U.sub.i represents the actual voltage output of the preamplifier circuit at the current moment; U.sub.i-1e.sup.?T/? represents the result of the voltage output U.sub.i-1 from the previous moment decayed by the charge leakage effect; c represents the linear coefficient between the output voltage of the preamplifier circuit and the force applied to the piezoelectric ceramic.

2. The system according to claim 1, wherein the post-processing module further comprises: a charge leakage dynamic compensation module, which compensates the voltage output U.sub.i of the preamplifier circuit at the current moment based on the change |u.sub.i?u.sub.i-1| in output voltage between adjacent moments and the circuit noise threshold u.sub.th1, as well as the change |u.sub.i?u.sub.i-1| in voltage and the voltage decay threshold u.sub.th2=U.sub.i-1(1?e.sup.?T/?) within the cycle time T.

3. The system according to claim 1, wherein the post-processing module further comprises: an offset current compensation module, which performs dynamic compensation U.sub.i=U.sub.i?K.sub.1.Math.i on the voltage value U.sub.i at the moment i based on a pre-calibrated slope value k.sub.1 of the deviation of the output voltage over time.

4. The system according to claim 1, wherein the post-processing module further comprises: a temperature compensation module, which performs dynamic compensation U.sub.i=U.sub.i?k.sub.2.Math.?T.sub.i on the voltage value U.sub.i at the moment i based on a pre-calibrated slope value k.sub.2 of the correlation between changes in output voltage and temperature changes, where ?T.sub.i is the change in ambient temperature relative to the moment i's ambient temperature.

5. A ultra-precision cutting quasi-static force measurement method based on piezoelectric ceramic sensor comprises the following steps: step one, continuously detect the voltage signal on the piezoelectric ceramic force sensor and record the output value U.sub.i of the charge amplifier at that moment; at the start of cutting, the initially detected output value U.sub.i of the charge amplifier is the actual output voltage U.sub.1 of the charge amplifier at that moment, and calculating the actual force applied to the piezoelectric ceramic force sensor for the first time; where c represents the linear coefficient between the output voltage of the charge amplifier and the force applied to the piezoelectric ceramic; step two, use the current moment's charge amplifier output value U.sub.i and the previous moment's charge amplifier output value U.sub.i-1 to calculate the dynamic varying voltage ?U.sub.i generated due to the dynamic force, $?U_i=U_i-U_{i-1}{e}^{-T/?};$ T represents the time interval between moments i and i?1; ? represents the time constant of charge leakage decay; U.sub.i-1e.sup.?T/? represents the result of the voltage output U.sub.i-1 from the previous moment decayed by the charge leakage effect; step three, calculate the dynamic varying force f.sub.i at the current moment, $f_i=\frac{?U_i}{c};$ step four, based on the solution f.sub.i of the dynamic varying force at each moment, the actual force F.sub.i acting on the piezoelectric ceramic force sensor at the current moment can be obtained by accumulating the dynamic varying forces from previous moment i, that is $F_i={.Math.}_{m=1}^i{f}_m=F_{i-1}+f_i.$

6. The method according to claim 5, wherein in step one, filter the voltage signal on the piezoelectric ceramic force sensor, as follows: record the change |u.sub.i?u.sub.i-1| in output voltage between two adjacent moments, the circuit noise threshold u.sub.th1, and the voltage decay threshold u.sub.th2=U.sub.i-1(1?e.sup.?T/?) within the cycle time T; when the change |u.sub.i?u.sub.i-1| in output voltage between two adjacent moments is greater than the circuit noise threshold u.sub.th1, it indicates that the voltage change is caused by an external dynamic force variation; the output voltage u.sub.i of that moment is used as the calculated value U.sub.i and is substituted into step three; when the change |u.sub.i?u.sub.i-1| in output voltage between two adjacent moments is less than or equal to the circuit noise threshold u.sub.th1, but the voltage change is greater than the decay threshold u.sub.th2, it indicates that the voltage change is induced by a dynamic force variation; the output voltage u.sub.i of that moment is used as the calculated value U.sub.i and is substituted into step three; when the change in output voltage |u.sub.i?u.sub.i-1| between two adjacent moments is less than or equal to the circuit noise threshold u.sub.th1, and the voltage change is less than or equal to the decay threshold u.sub.th2, the result u.sub.i-1e.sup.?T/? of the voltage u.sub.i-1 decay from the previous moment is used as the current moment's calculated value U.sub.i and is substituted into step three.

7. The method according to claim 5, wherein in step one, an offset current compensation is performed: a slope value k.sub.1 related to the deviation of the output voltage over time is pre-calibrated to give dynamic compensation U.sub.i of the voltage value U.sub.i over the moment i; $U_1=U_i-k_1.Math.i.$

8. The method according to claim 5, wherein in step one, a temperature compensation is performed: a slope value k.sub.2 related to the deviation of the output voltage over time is pre-calibrated to give dynamic compensation U.sub.i of the voltage value U.sub.i over the moment i. $U_i=U_i-k_2.Math.?T_i,$ ?T.sub.i represents the change in ambient temperature relative to the moment i's ambient temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 illustrates a comparison between the actual output and ideal output of the quasi-static force loading and unloading for the piezoelectric ceramic force sensor.

[0050] FIG. 2 is the principle block diagram of the invention;

[0051] FIG. 3 is a schematic diagram illustrating the principle of the quasi-static force measurement algorithm based on dynamic compensation for piezoelectric ceramic charge leakage;

[0052] FIG. 4 is the block diagram of the quasi-static force measurement algorithm based on charge leakage dynamic compensation;

[0053] FIG. 5 is a schematic diagram showing the effect of bias current on the quasi-static force algorithm;

[0054] FIG. 6 is a schematic diagram showing the effect of temperature on the quasi-static force algorithm;

[0055] FIG. 7 compares the measurement results of the ultra-precision cutting quasi-static force perception system based on the piezoelectric ceramic sensor with those from a commercial dynamometer;

[0056] FIG. 8 is the circuit schematic diagram of the invention; and

[0057] FIG. 9 is the PCB diagram of the technical solution of the invention.

DESCRIPTION OF THE EMBODIMENTS

[0058] Below, in conjunction with the accompanying figures, provides a further detailed explanation of the specific embodiments of the present invention.

[0059] As shown in FIGS. 1-9, the ultra-precision cutting device based on the piezoelectric ceramic sensor described by this invention is an enhancement to traditional single-point diamond ultra-precision cutting systems (such as fast tool servo devices, slow tool servo devices, etc.). By integrating a piezoelectric ceramic force sensing unit, it aims to achieve online monitoring of cutting forces during the ultra-precision cutting process at the tool end, thereby enabling online monitoring of the machining state.

[0060] A ultra-precision cutting quasi-static force measurement system based on piezoelectric ceramic sensor includes:

[0061] A piezoelectric ceramic force sensing unit 1, located at the machining end of the ultra-precision cutting system 14, and used for mounting the single-point diamond tool 13; The piezoelectric ceramic force sensing unit 1 is a piezoelectric ceramic force sensor integrated into the ultra-precision cutting device, which produces weak charge signals during the application of force;

[0062] The piezoelectric ceramic force sensing unit 1, when subjected to the force exerted by the single-point diamond tool 13, generates a charge signal that is transmitted to an external post-processing module. This post-processing module includes: [0063] A preamplifier circuit 5 for amplifying the signals detected by the piezoelectric ceramic force sensing unit 1; [0064] A low-pass filter circuit 6 for filtering the output signal from the preamplifier circuit; [0065] An ADC module 7 for converting the voltage signal passed from the low-pass filter circuit 6 into a corresponding digital signal; [0066] A DSP signal processor 9 for real-time processing of the digital signal and transmitting the processed data to a computer 8; the computer may be an ordinary PC; [0067] The computer 8 calculates the actual force f.sub.i acting on the piezoelectric ceramic force sensor based on the dynamic variation of forces at each moment, and obtains the actual force F.sub.i acting on the piezoelectric ceramic force sensor at the moment i by accumulating the dynamic changing force at previous moment i;

[00008]$F_i=F_{i-1}+\frac{U_i-U_{i-1}{e}^{-T/?}}{c};$

where [0068] T represents the time interval between moments i and i?1; [0069] ? represents the time constant of charge leakage decay; [0070] U.sub.i represents the actual voltage output of the preamplifier circuit at the current moment; [0071] U.sub.i-1e.sup.?T/? represents the result of the voltage output U.sub.i-1 from the previous moment decayed by the charge leakage effect; [0072] c represents the linear coefficient between the output voltage of the preamplifier circuit and the force applied to the piezoelectric ceramic, which can be calibrated in advance according to the specific preamplifier circuit used. [0073] e represents the natural constant e.

[0074] The time interval T depends on the computational power of the processor, which affects the frequency of real-time processing. The processor used in this invention has an interval of about 1 ms, corresponding to 1 kHz. Theoretically, the stronger the computational power of the processor, the shorter the time interval T and the higher the precision.

[0075] Preferably, the post-processing module also includes: a charge leakage dynamic compensation module 10, which compensates the voltage output U.sub.i of the preamplifier circuit at the current moment based on the change |u.sub.i?u.sub.i-1| in output voltage between adjacent moments and the circuit noise threshold u.sub.th1, as well as the change |u.sub.i?u.sub.i-1| in voltage and the voltage decay threshold u.sub.th2=U.sub.i-1(1?e.sup.?T/?) within the cycle time T.

[0076] Preferably, the post-processing module also includes: an offset current compensation module 11, which performs dynamic compensation U.sub.i=U.sub.i?k.sub.1.Math.i on the voltage value U.sub.i at the moment i based on a pre-calibrated slope value k.sub.1 of the deviation of the output voltage over time.

[0077] Preferably, the post-processing module also includes: a temperature compensation module 12, which performs dynamic compensation U.sub.i=U.sub.i?k.sub.2.Math.?T; on the voltage value U.sub.i at the moment i based on a pre-calibrated slope value k.sub.2 of the correlation between changes in output voltage and temperature changes, where ?T.sub.i is the change in ambient temperature relative to the moment i's ambient temperature.

[0078] A ultra-precision cutting quasi-static force measurement method based on piezoelectric ceramic sensor includes the following steps:

[0079] Step 1, continuously detect the voltage signal on the piezoelectric ceramic force sensor and record the output value U.sub.i of the charge amplifier at that moment; if the dynamic varying force acting on the piezoelectric ceramic force sensor at any moment is f.sub.i, then the contribution of this dynamic force to the output of the charge amplifier at that moment is ?U.sub.i,

[00009]$\begin{array}{cc}?U_i=c{f}_i;& \left(1\right)\end{array}$

[0080] At the start of cutting, the initially detected output value U.sub.i of the charge amplifier is the actual output voltage U.sub.1 of the charge amplifier at that moment, and the initial dynamic varying force f.sub.1 is the actual force F.sub.1 initially applied to the piezoelectric ceramic force sensor,

[00010]$F_1=\frac{U_1}{c};$

[0081] Step 2, use the current moment's charge amplifier output value U.sub.i and the previous moment's charge amplifier output value U.sub.i-1 to calculate the dynamic varying voltage ?U.sub.i generated due to the dynamic force,

[00011]$\begin{array}{cc}?U_i=U_i-U_{i-1}{e}^{-T/?};& \left(2\right)\end{array}$

[0082] Step 3, calculate the dynamic varying force f.sub.i at the current moment,

[00012]$\begin{array}{cc}{f}_i=\frac{?U_i}{c};& \left(3\right)\end{array}$

[0083] c represents the linear coefficient between the output voltage of the charge amplifier and the force applied to the piezoelectric ceramic;

[0084] Step 4, based on the solution f.sub.i of the dynamic varying force at each moment, the actual force F.sub.i acting on the piezoelectric ceramic force sensor at the current moment can be obtained by accumulating the dynamic varying forces from previous moment i, that is

[00013]$\begin{array}{cc}{F}_i={.Math.}_{m=1}^i{f}_m=F_{i-1}+f_i;& \left(4\right)\end{array}$

[0085] Preferably, in Step 1, as shown in FIG. 4, filter the voltage signal on the piezoelectric ceramic force sensor, as follows: [0086] Record the change |u.sub.i?u.sub.i-1| in output voltage between two adjacent moments, the circuit noise threshold u.sub.th1, and the voltage decay threshold u.sub.th2=U.sub.i-1(1?e.sup.?T/?) within the cycle time T; [0087] When the change |u.sub.i?u.sub.i-1| in output voltage between two adjacent moments is greater than the circuit noise threshold u.sub.th1, it indicates that the voltage change is caused by an external dynamic force variation. The output voltage u.sub.i of that moment is used as the calculated value U.sub.i and is substituted into formula (3) of Step 3; [0088] When the change |u.sub.i?u.sub.i-1| in output voltage between two adjacent moments is less than or equal to the circuit noise threshold u.sub.th1, but the voltage change is greater than the decay threshold u.sub.th2, it indicates that the voltage change is induced by a dynamic force variation. The output voltage u.sub.i of that moment is used as the calculated value U.sub.i and is substituted into formula (3) of Step 3; [0089] When the change in output voltage |u.sub.i?u.sub.i-1| between two adjacent moments is less than or equal to the circuit noise threshold u.sub.th1, and the voltage change is less than or equal to the decay threshold u.sub.th2, the result u.sub.i-1e.sup.?T/? of the voltage u.sub.i-1 decay from the previous moment is used as the current moment's calculated value U.sub.i and is substituted into formula (3) of Step 3.

[0090] Preferably, in Step 1, as shown in FIG. 5, the offset current is an inherent phenomenon of the charge amplifier. The presence of the offset current leads to a fixed slope deviation in the output voltage of charge amplifier without a powerful input, and the effect of bias current on the output of charge amplifier. Since the effect of the bias current on the output voltage of the charge amplifier is a linear offset, dynamic compensation U.sub.i for the momentary voltage value is achieved by pre-calibrating the slope value k.sub.1 related to the deviation of the output voltage U.sub.i over the moment i. This allows for the implementation of bias current compensation.

[00014]$U_i=U_i-k_1.Math.i.$

[0091] Preferably, in Step 1, as shown in FIG. 6, changes in the ambient temperature can cause deviations in the output voltage of the charge amplifier, thereby affecting the force measurement values calculated based on the output voltage of the charge amplifier. The influence of temperature changes on the output voltage of the charge amplifier shows a linear negative correlation with temperature change. Hence, by pre-calibrating the slope value k.sub.2 related to the change in output voltage with temperature variation, dynamic compensation U.sub.i for the voltage value U.sub.i at the moment i is performed. This allows for the implementation of temperature compensation;

[00015]$U_i=U_i-k_2.Math.?T_i,$

[0092] ?T.sub.i represents the change in ambient temperature relative to the moment i's ambient temperature.

[0093] In summary, the function of measuring quasi-static forces with the piezoelectric ceramic force sensor is realized based on charge leakage dynamic compensation, and the precision of quasi-static force detection is achieved through the offset current compensation module and temperature compensation module.

[0094] To further verify the effectiveness of the method described in this invention, a comparison was made with a commercial dynamometer, and the results are shown in FIG. 7. The force loading method shown in FIG. 7 involves continuous loading and unloading of quasi-static forces.

[0095] In the upper part of FIG. 7, the uncompensated quasi-static force detection results of the piezoelectric ceramic force sensor are displayed. It can be observed that although the sensor outputs a sensitive voltage change at the moment of force variation, this change cannot be sustained, which causes it can't effectively determine the actual force applied to the piezoelectric ceramic force sensor at any given moment.

[0096] The middle part of FIG. 7 shows the compensated quasi-static force detection results of the piezoelectric ceramic force sensor according to this invention. It can be seen that not only is there a sensitive change at the moment of force application, but this change is also maintained consistently, thereby enabling the measurement of quasi-static forces; that is, it reflects the actual magnitude of the force acting on the piezoelectric ceramic force sensor at any moment.

[0097] The lower part of FIG. 7 displays the detection results from the commercial dynamometer. It is evident that the commercial dynamometer can also respond and maintain changes to quasi-static forces. However, it has greater signal noise, which makes it less sensitive in force detection compared to the method described in this invention, and it is unable to effectively and accurately sense ultra-low cutting forces.

[0098] The actual detection process of this system: Each detection starts from zero. At the beginning of cutting, the first detected output value U.sub.i of the charge amplifier is the actual output voltage U.sub.1 of the charge amplifier at that moment, and the first actual force F.sub.1=U.sub.1/c is obtained through the formula. During the second detection, the current output voltage U.sub.2 is used as a basis, and is subtracted the residual charge U.sub.1e.sup.?T/? from U.sub.1 due to charge leakage to obtain the actual increased voltage ?U.sub.2 for the second detection. Then based on the actual increased voltage ?U.sub.2, the actual dynamic changing force f.sub.2 is calculated. By accumulating the dynamic changing force f.sub.2 based on the F.sub.1, the actual force F.sub.2 acting on the single-point diamond tool 13 at the current moment can be obtained, and so forth.

[0099] The above embodiments and descriptions in the specification are only to illustrate the principles of the invention. Under the premise of not departing from the spirit and scope of the invention, there may be various modifications and improvements, which fall within the scope of the invention as claimed. The scope of protection sought by the invention is defined by the attached claims and their equivalents.