CN108453741B - Flexible servo control method for industrial robot - Google Patents
Flexible servo control method for industrial robot Download PDFInfo
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- CN108453741B CN108453741B CN201810331540.6A CN201810331540A CN108453741B CN 108453741 B CN108453741 B CN 108453741B CN 201810331540 A CN201810331540 A CN 201810331540A CN 108453741 B CN108453741 B CN 108453741B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
- B25J9/00—Programme-controlled manipulators
- B25J9/16—Programme controls
- B25J9/1602—Programme controls characterised by the control system, structure, architecture
- B25J9/1607—Calculation of inertia, jacobian matrixes and inverses
Abstract
The invention relates to a flexible servo control method of an industrial robot, which comprises the following steps: establishing a dynamic compensation model, and performing joint gravity compensation by adopting a recursive Newton Euler inverse dynamic algorithm to enable the joint to be in a gravity balance state; establishing a friction force compensation model, wherein in a static state, the model is established in a mode that a high-frequency jitter signal with the amplitude close to a static friction boundary is added to a force front feed joint; designing a buffeting signal, wherein a buffeting amplitude at the position of a motor is enabled to track a reference buffeting amplitude by adopting closed-loop integral control; and (4) compensating the integral feedback residual value, and compensating the integral residual value through a switching transition process. The invention provides a flexible servo control method suitable for a general industrial robot control system, which can be widely applied to a small-range high-precision operation scene without increasing the assembly cost.
Description
Technical Field
The invention relates to the technical field of industrial robot intelligent control, in particular to a flexible servo control method for an industrial robot.
Background
In recent years, with the increasing degree of industrial automation, the application fields of industrial robots have been developed from industries such as automobiles, electronic appliances, and machines to other application fields, and become an indispensable part of many industrial fields. Conventional industrial robot control is based on position control, i.e. the robot is controlled to follow a certain predetermined trajectory. Such a control mode method enables the robot to be competent for most track following tasks, but for more and more application scenarios, especially for small-range high-precision operation tasks such as close tolerance assembly and workpiece finish machining, position control will be difficult to be competent due to a series of uncertain factors such as workpiece mounting positions. Therefore, modern industries place higher demands on the application flexibility and response sensitivity of robots. Many methods currently exist to monitor the contact state of the robot with the external environment by installing an external sensor, such as a force sensor or a vision system, while continuously modifying the slight position uncertainty deviation to achieve a small-scale high-precision operation.
Although these conventional control methods can provide a robot with a relatively good application effect in a wide-range remote operation, they have several disadvantages: 1) in order to meet the requirements of high precision and rapidity of tracking, a servo control system is often required to have strong rigidity, namely, a relatively high closed-loop feedback gain, otherwise, a relatively large tracking error and response delay occur, but the servo control system with high rigidity has poor capability of complying with the external environment, and if a trajectory planning has an error or an obstacle exists on a motion path, the robot collides with a working platform or the obstacle with a relatively large force, so that a workpiece or even the robot is damaged. 2) The additional sensors and control software packages inevitably result in higher complexity, more expensive manufacturing cost, and even lower payload of the robot control system, which is a serious departure from the design concept of low-cost, low-load robots.
Disclosure of Invention
The invention aims to provide a flexible servo control method for an industrial robot, which is used for overcoming the technical defects in the prior art.
In order to achieve the above object, the present invention provides a flexible servo control method for an industrial robot, comprising:
step a, establishing a dynamic compensation model, and performing joint gravity compensation by adopting a recursive Newton Euler inverse dynamic algorithm to enable a joint to be in a gravity balance state;
b, establishing a friction force compensation model, wherein in a static state, the model is established in a mode that a high-frequency shaking signal with the amplitude close to a static friction boundary is added to a force front feed joint;
step c, designing a buffeting signal, and enabling a buffeting amplitude of the motor position to track a reference buffeting amplitude by adopting closed-loop integral control, wherein: the buffeting signal generator generates a periodic buffeting signal; the vibration amplitude is estimated from the collected joint position information; the closed loop integral outputs a multiplier to control the vibration amplitude of the amplified buffeting signal;
and d, compensating the integral feedback residual value, and compensating the integral residual value through a switching transition process.
Further, in the step a, the method includes:
step a1, calculating the speed and acceleration of each mechanical arm;
step a2, calculating the force required by each mechanical arm to realize acceleration;
step a3, calculating the force provided by a joint motor required by each mechanical arm to realize gravity compensation;
wherein:
Further, in the above step a3,
velocity of joint
The data of the passing position is obtained by the low-pass difference method of the formula (2):
in the formula, KlpRepresenting the conversion coefficients, where q represents the joint position, obtained by the motor encoder.
Furthermore, in the step c, in a static state, a high-frequency shaking signal with the amplitude close to a static friction boundary is added through the force front feeding joint, the mechanical arm moves after the positive half period or the negative half period corresponding to the external force and the high-frequency shaking signal are superposed, and then the compensation is carried out by using a friction force compensation method in a motion state,
wherein:
Further, the step d includes:
d1, at the moment of switching, setting the proportionality coefficient to zero, reserving or properly increasing the integral coefficient, setting the reference position instruction as the current position, and adding a buffeting closed loop;
step d2, waiting for the system to stabilize, wherein the integrator residual value is equal to the gravity compensation value, and the process is defined as a transition process;
and d3, setting the integral coefficient to zero, setting a position reference value and a proportional gain, and keeping a buffeting closed loop to realize the switching of the compliance control.
Compared with the prior art, the flexible servo control method applicable to the control system of the general industrial robot has the beneficial effects that the compensation of the driving force required to be overcome in the joint motion process of gravity, friction and the like is completed through the dynamic model and the recursive solving algorithm and by combining the position, the speed and other information acquired by the joint motor of the robot. In a state close to a standstill, compensation of the static friction is achieved by closed-loop buffeting control. Under the condition of achieving the force compensation, the position closed-loop control loop gain is greatly reduced, so that the robot is in a state close to free motion, and the compliance capability of the industrial robot to the external environment is improved. The simple flexible servo control method for the robot can be widely applied to a small-range high-precision operation scene under the condition that the assembly cost is not required to be increased.
Furthermore, the flexible servo control method is adopted, the capability of the industrial robot to conform to the external environment is improved, an additional sensor is not required to be configured, the manufacturing cost is low, the design process is simple, and the loss of the load capacity is small.
Furthermore, the adopted buffeting moment feedforward design method can effectively reduce the traction force overcoming the coulomb friction in the friction dead zone, increase the sensitivity of external force and simultaneously avoid the impact at the moment of being separated from the static state, thereby improving the precision of small-range movement.
Further, the adopted design method of the closed-loop buffeting signal realizes the automatic adjustment of the buffeting amplitude value, so that the control process does not depend on uncertain coulomb friction coefficients any more;
furthermore, the integral feedback residual value compensation method effectively realizes zero clearing of the integrator in the rigid-flexible switching process and reduces the requirement for observing the state inside the servo system.
Drawings
Fig. 1 is a block diagram of a flexible servo control method of an industrial robot according to an embodiment of the invention;
FIG. 2 is a graph of time versus moment for various forces of an industrial robot in accordance with an embodiment of the present invention;
fig. 3 is a block diagram of a closed-loop buffeting structure for an industrial robot of an embodiment of the present invention;
fig. 4 is a block diagram of an industrial robot integrated feedback residual compensation according to an embodiment of the present invention.
Detailed Description
The above and further features and advantages of the present invention are described in more detail below with reference to the accompanying drawings.
Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only for explaining the technical principle of the present invention, and are not intended to limit the scope of the present invention.
It should be noted that in the description of the present invention, the terms of direction or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, which are only for convenience of description, and do not indicate or imply that the device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.
Furthermore, it should be noted that, in the description of the present invention, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood as the case may be, for a seat mechanism of the art.
Referring to fig. 1, which are respectively block diagrams of a flexible servo control method of an industrial robot according to the present invention, the control process of the present embodiment includes:
step a, establishing a dynamic compensation model; and performing joint gravity compensation by adopting a recursive Newton Euler inverse dynamics algorithm to enable the joint to be in a gravity balance state.
The method comprises the following implementation steps:
step a1, calculating the speed and acceleration of each mechanical arm;
step a2, calculating the force required by each mechanical arm to realize acceleration;
step a3, calculating the force provided by a joint motor required by each mechanical arm to realize gravity compensation;
wherein:
Wherein, the joint position q is obtained by a motor encoder, and the joint speed
The data of the passing position is obtained by the low-pass difference method of the formula (2):
in the formula, KlpRepresenting the conversion coefficient.
B, establishing a friction force compensation model; in a static state, a model is established by adding a high-frequency jitter signal with the amplitude close to a static friction boundary to the force front feed joint.
In the motion state, the compensation of the friction force only needs to add a motor compensation force with the same speed direction, and the magnitude of the compensation force is approximately the sum of viscous friction and coulomb friction described by a linear model. However, in a static state, coulomb friction force changes in an interval, the magnitude and the direction of the coulomb friction force are difficult to determine, and the motion of the mechanical arm must overcome the friction force, so that the mechanical arm needs larger environmental force to overcome the coulomb friction from static to dynamic in a flexible servo state, and the sensitivity of the mechanical arm to the external environment is reduced, namely when the environmental force is smaller, the mechanical arm cannot respond to the external environment, and corresponding motion is generated. For improving the sensitivity of the mechanical arm to the external force, the embodiment adopts a buffeting control method, that is, in a static state, a high-frequency shaking signal with the amplitude close to a static friction boundary is added through a force front feeding joint, when the external force and a corresponding positive (negative) half period of the high-frequency shaking signal are superposed, the mechanical arm is easy to move, and then compensation can be performed by using a friction force compensation method in a moving state, as shown in the following formula, by combining with the method shown in fig. 3.
Wherein:
Step c, designing a buffeting signal;
due to environmental changes and motion state changes, the identification of the friction coefficient is inaccurate, and the amplitude of the buffeting signal is difficult to solidify, so that closed-loop buffeting is designed to realize the automatic adjustment of the buffeting amplitude, a design block diagram is shown in fig. 3, and the design principle is that closed-loop integral control is adopted to enable the buffeting amplitude at the position of the motor to track the reference buffeting amplitude. Wherein: the buffeting signal generator generates a periodic buffeting signal; the vibration amplitude is estimated from the collected joint position information; the closed loop integral outputs a multiplier for controlling the magnitude of the vibration of the amplified dither signal.
D, compensating the integral feedback residual value, and compensating the integral residual value through a switching transition process;
if the high-speed rigid motion state is switched to the flexible motion state, the closed-loop gain at the switching moment is greatly reduced, but the closed-loop integrator still retains the integral value at the current moment, and how to counteract the integral value is the key of switching. This embodiment achieves compensation of the integrated residual value by introducing a transition process as shown in fig. 4. The method comprises the following specific steps:
d1, at the moment of switching, setting the proportionality coefficient to zero, reserving or properly increasing the integral coefficient, setting the reference position instruction as the current position, and adding a buffeting closed loop;
step d2, waiting for the system to stabilize, wherein the integrator residual value is equal to the gravity compensation value, and the process is defined as a transition process;
and d3, setting the integral coefficient to zero, setting a position reference value and a proportional gain, and keeping a buffeting closed loop to realize the switching of the compliance control.
According to the embodiment, the flexible servo control method is adopted, so that the capability of the industrial robot for following the external environment is improved, an additional sensor is not required to be configured, the manufacturing cost is low, the design process is simple, and the loss of the load capacity is small;
the adopted buffeting moment feedforward design method can effectively reduce the traction force overcoming the coulomb friction in the friction dead zone, increase the sensitivity of external force and simultaneously avoid the impact at the moment of separating from the static state, thereby improving the precision of small-range movement;
the adopted closed-loop buffeting signal design method realizes the automatic adjustment of buffeting amplitude, so that the control process does not depend on uncertain coulomb friction coefficients any more;
the integral feedback residual value compensation method effectively realizes zero clearing of the integrator in the rigid-flexible switching process and reduces the requirement for observing the state inside the servo system.
So far, the technical solution of the present invention has been described in connection with the preferred embodiments shown in the accompanying drawings, but it is apparent to those skilled in the art that the scope of the present invention is not limited to these specific embodiments. Equivalent modifications or substitutions of features relative to the prior art can be made to the seat mechanism of the prior art without departing from the principle of the invention, and the technical solutions after such modifications or substitutions are all within the protective scope of the invention.
Claims (5)
1. A flexible servo control method for an industrial robot is characterized by comprising the following steps:
step a, establishing a dynamic compensation model, and performing joint gravity compensation by adopting a recursive Newton Euler inverse dynamic algorithm to enable a joint to be in a gravity balance state;
b, establishing a friction force compensation model, wherein in a static state, the model is established in a mode that a high-frequency shaking signal with the amplitude close to a static friction boundary is added to a force front feed joint;
step c, designing a buffeting signal, and enabling a buffeting amplitude at the position of the motor to track a reference buffeting amplitude by adopting closed-loop integral control;
d, compensating the integral feedback residual value, and compensating the integral residual value through a switching transition process;
in the step a, the method comprises the following steps:
step a1, calculating the speed and acceleration of each mechanical arm;
step a2, calculating the force required by each mechanical arm to realize acceleration;
step a3, calculating the force provided by a joint motor required by each mechanical arm to realize gravity compensation;
wherein:
2. An industrial robot flexible servo control method according to claim 1, wherein in the above step a3,
velocity of joint
Data passing position passing equation (2) Low pass DifferenceThe method comprises the following steps:
in the formula, KlpThe conversion coefficient is represented, where q represents the joint position, obtained by the motor encoder.
3. A flexible servo control method for an industrial robot according to claim 1, wherein in step b, the dither signal generator generates a periodic dither signal; the vibration amplitude is estimated from the collected joint position information; the closed loop integral outputs a multiplier for controlling the magnitude of the vibration of the amplified dither signal.
4. The flexible servo control method of industrial robot as claimed in claim 1, wherein in the step c, a high frequency dithering signal with amplitude close to static friction boundary is added through the force front feeding joint in static state, the mechanical arm is moved after the positive or negative half period corresponding to the external force and the high frequency dithering signal are overlapped, then compensation is carried out by using the friction force compensation method in motion state,
wherein:
5. A flexible servo control method of an industrial robot according to claim 1, wherein said step d comprises:
d1, at the moment of switching, setting the proportionality coefficient to zero, reserving or properly increasing the integral coefficient, setting the reference position instruction as the current position, and adding a buffeting closed loop;
step d2, waiting for the system to stabilize, wherein the integrator residual value is equal to the gravity compensation value, and the process is defined as a transition process;
and d3, setting the integral coefficient to zero, setting a position reference value and a proportional gain, and keeping a buffeting closed loop to realize the switching of the compliance control.
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