US 11,484,982 B2 · Online CNC machine tool geometric/thermal error measurement and compensation system

Abstract

An online geometric/thermal error measurement and compensation system for computer numerically controlled (CNC) machine tools belonging to the technical field of error testing and compensation of CNC machine tools. The online CNC machine tool geometric/thermal error measurement and compensation system includes two parts: the hardware platform and the measurement and compensation software. The hardware platform includes a unidirectional acceleration sensor, a precision integrated circuit (IC) temperature sensor, a multi-channel temperature data collector, and a geometric/thermal error measurement and compensation host. The error measurement and compensation software runs in the geometric/thermal error measurement and compensation host and realizes testing and compensation of geometric and thermal errors in machine tools, which are communicated to the FANUC CNC system.

An online geometric/thermal error measurement and compensation system for CNC machine tools, the online CNC machine tool geometric and/or thermal error measurement and compensation system is mainly comprised of two parts:

a hardware of measurement and compensation system and a software of measurement and compensation system;
the hardware of measurement and compensation system comprises a unidirectional acceleration sensor, a digital precision IC temperature sensor, a multi-pass channel temperature data logger and a geometric and/or thermal error measurement and compensation host;
geometric and/or thermal error data processing and compensation, communication with numerical control system and reading and writing data are controlled via the software of measurement and compensation of the system operated in the geometric and/or thermal error measurement and compensation host;
wherein
the unidirectional acceleration sensor is connected to the geometric/thermal error measurement and compensation host via a coaxial shielded cable and the acceleration signal is sent to the geometric and/or thermal error measurement and compensation host in analog form;
the digital precision IC temperature sensor connects to a multi-pass channel temperature data logger through a four-core shielded cable and sends temperature data to a multi-pass channel temperature data logger based on a single-line bidirectional communication protocol;
the multi-pass channel temperature data logger can connect to up to ten temperature sensors;
the multi-pass channel temperature data logger connects to the geometric and/or thermal error measurement and compensation host through the three-core shielded cable and sends the aggregated temperature data to the geometric and/or thermal error measurement and compensation host based on the Modbus RTU communication protocol;
the geometric/thermal error measurement and compensation host connects to the FANUC CNC through a twisted pair cross cable and the communication is carried out based on the FOCAS II network communication protocol;
software of measurement and compensation system:
(1) based on the acceleration signal, the straightness error of the feed axis of the machine tool is obtained by applying the geometric error identification algorithm of the feed axis;
the geometric error identification algorithm of the feed axis is
{
s
⁡
(
t
)
=
∫
∫
a
⁡
(
t
)
⁢
dt
-
1
2
⁢
a
0
⁢
t
2
-
v
0
⊥
⁢
t
-
x
0
⊥
x
⁡
(
t
)
=
v


(
1
)
where s(t) is the real-time displacement, x01 is the initial displacement in the vertical direction, v01 is the initial velocity perpendicular to the axial direction, a0 is the DC component of the acceleration signal, a(t) is the real-time acceleration, vII is the constant velocity along the axial direction, and x(t) the axial real-time length;
solving Equation (1), the relationship between the real-time displacement s(t) and the axial test stroke x is obtained as
s
⁡
(
x
)
=
∫
∫
a
⁡
(
x
/
v


)
⁢
d
⁢
t
-
1
2
⁢
a
0
⁡
(
x
v


)
2
-
v
0
⊥
⁢
t
-
x
0
(
2
)
then, the two-point line connection method is applied to calculate the straightness error of the feed axis according to s(x);
the specific calculation is
E
s
⁡
(
x
)
=
s
⁡
(
x
)
-
s
⁡
(
end
)
-
s
⁡
(
0
)
L
⁢
x
(
3
)
where Es(x) is the straightness error, L is the total test stroke, x is the test stroke, s(end) is the final displacement at the end of the test, and s(0) is the displacement at the starting point of the test;
(2) based on the position and the temperature signal applied to the feed shaft thermal error model, thermal errors are predicted in real time;
dividing the feed shaft thermal error model screw into N segments, each of length l, the thermal error is calculated as
⁢
E
f
⁡
(
m
,
t
)
=
∑
i
=
1
m
⁢
k
×
l
×
(
T
i
⁡
(
t
)
-
T
0
)
(
4
)
T
i
⁡
(
t
)
=
T
i
⁡
(
t
-
Δ
⁢
⁢
t
)
+
γ
×
Q
-
{
α
×
[
T
i
⁡
(
t
-
Δ
⁢
t
)
-
T
i
-
1
⁡
(
t
-
Δ
⁢
t
)
]
+
[
T
i
⁡
(
t
-
Δ
⁢
t
)
-
T
i
+
1
⁡
(
t
-
Δ
⁢
t
)
]
l
+
β
×
[
T
i
⁡
(
t
-
Δ
⁢
t
)
-
T
f
⁡
(
t
-
Δ
⁢
t
)
]
}
×
Δ
⁢
⁢
t
where Ef(m,t) is the calculated value of thermal error to the m-th section of the screw at the current time, Ti(t) is the temperature corresponding to the i-th section of the screw at the current time, Q is the heat generated through the nut of the screw in each segment, Ti(t−Δt) is the temperature to the i-th section of the screw at the previous time, Tf(t−Δt) is the temperature of the air in contact with the surface of the screw at the previous moment, Δt is the sampling period, and k, α, β, and γ are coefficients;
(3) to realize communication with FANUC numerical control system based on the FOCAS II protocol, reading of the machine tool coordinates and writing of the error compensation value, and compensation based on extended external mechanical coordinate origin offset function, the following steps are performed:
1) set “embedded/PCMCIA” as a valid ethernet device in the FANUC control system;
2) set relevant parameters of the “expanded external machine coordinate origin shift function” and turn on the function;
3) the measurement and compensation system software establishes a connection with the IP address and port number of the FANUC numerical control system;
once the connection is successful, the mechanical coordinates of the feed axis are read, data from the unidirectional acceleration sensor and the temperature sensor are simultaneously acquired, and the geometry and/or heat is calculated;
the integrated error compensation value is used to write the error compensation value to the numerical control system;
the current integrated geometric and/or thermal error compensation value is calculated as follows:
C(x,t)=−[Es(x)+Ef(m,t)] (5).

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Online CNC machine tool geometric/thermal error measurement and compensation system

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Online CNC machine tool geometric/thermal error measurement and compensation system

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Abstract

Claims1