CN109202721B - Control method of grinding process, grinding device and robot grinding system - Google Patents
Control method of grinding process, grinding device and robot grinding system Download PDFInfo
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- CN109202721B CN109202721B CN201710534319.6A CN201710534319A CN109202721B CN 109202721 B CN109202721 B CN 109202721B CN 201710534319 A CN201710534319 A CN 201710534319A CN 109202721 B CN109202721 B CN 109202721B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B51/00—Arrangements for automatic control of a series of individual steps in grinding a workpiece
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Abstract
The invention discloses a control method of a grinding process, a grinding device and a robot grinding system, wherein the control method specifically comprises the following steps: in the initial stage of grinding, speed control is executed to control the speed of the grinding tool relatively approaching to the processed workpiece; detecting the pressure between the grinding tool and the processed workpiece, judging the contact pressure between the grinding tool and the processed workpiece and the preset contact pressure, stopping executing speed control when the detected contact pressure is greater than or equal to the preset contact pressure, executing torque control to control the output torque of the driving part to enable the pressure between the grinding tool and the processed workpiece to be gradually increased to a preset grinding pressure range from the contact pressure in the current state, and maintaining the contact pressure to be in the preset grinding pressure range to grind the processed workpiece; the control method can play a good role in force buffering, protect the grinding tool well, prolong the service life of the grinding tool and increase the surface processing precision of the processed workpiece.
Description
Technical Field
The invention relates to the technical field of polishing, in particular to a control method of a polishing process, a polishing device and a robot system.
Background
The robot grinding system is an automatic production system for grinding products by using a robot. The system can quickly and effectively remove redundant materials on the surface of a processed part, so that the robot grinding system is widely applied to various industrial fields.
The grinding quality of the surface of the machined part is a constant focus of attention by those skilled in the art.
Disclosure of Invention
In order to solve the above technical problems, the present invention provides a method for controlling a polishing process,
in the initial grinding stage, a speed control strategy is executed to control the speed of the grinding tool relatively close to the processed workpiece;
detecting the pressure between the grinding tool and the processed workpiece in real time, judging the contact pressure between the grinding tool and the processed workpiece and the preset contact pressure, stopping executing the speed control strategy when the detected contact pressure is greater than or equal to the preset contact pressure, executing a torque control strategy to control the output torque of a driving part to enable the pressure between the grinding tool and the processed workpiece to be gradually increased to a preset grinding pressure range from the contact pressure in the current state, and maintaining the contact pressure to be in the preset grinding pressure range to grind the processed workpiece.
Two control parameters are set in the control method of the invention: the preset contact pressure F0 and the preset grinding pressure F1 are that in the grinding contact process of the grinding tool and the processed workpiece, the pressure between the grinding tool and the processed workpiece reaches a smaller preset contact pressure, then the output torque of the driving part is continuously increased, the preset contact pressure F0 is increased to a preset grinding pressure range, and the increase control of the pressure between the grinding tool and the processed workpiece is divided into two stages: the first stage is to increase the initial contact pressure F' to the preset contact pressure F0, and the second stage is to increase the preset contact pressure F0 to a predetermined grinding pressure range. Here, if the grinding tool and the workpiece are relatively brought close to each other by torque control until the grinding tool and the workpiece are brought into contact with each other, the impact when the grinding tool and the workpiece are brought into contact with each other is large. On the other hand, when the grinding tool and the workpiece are relatively brought close to each other by the speed control until the grinding tool and the workpiece are brought into contact with each other, since the speed is controlled, the impact when the grinding tool and the workpiece are brought into contact with each other can be reduced. Therefore, the control method provided by the invention can play a good role in buffering force, protecting the grinding tool well, prolonging the service life of the grinding tool and increasing the surface processing precision of the processed workpiece.
Optionally, while the torque control strategy is executed to grind the workpiece, the following steps are also performed: and detecting the current grinding position in real time, judging whether the current grinding position reaches the grinding lower limit position range, if so, stopping executing the torque control strategy, and executing the position control strategy to keep the grinding tool or the processed workpiece in the grinding lower limit position range in the moving process of the mechanical arm.
Therefore, excessive grinding of the workpiece is avoided by controlling the grinding position in real time.
Optionally, the following steps are further executed in the process of executing the position control strategy: and judging whether the contact pressure between the grinding tool and the workpiece is larger than the upper limit value of the preset grinding pressure range, if so, stopping executing the position control strategy, and executing the torque control strategy to control the output torque of the driving part so as to adjust the contact pressure between the grinding tool and the workpiece to the preset grinding pressure range.
Optionally, a pressure sensor is arranged between the driving component and a grinding tool assembly including a grinding tool, and is used for detecting the pressure between the grinding tool and the workpiece; the control method also corrects the detected pressure, and the specific correction method comprises the following steps: and correcting the detected pressure by considering the self gravity factor of the grinding tool assembly so as to determine the actual torque required to be output by the driving part.
Thus, the accuracy of the output torque of the driving member can be improved to increase the accuracy of control, and the accuracy of the ground surface can be further improved.
Optionally, the correction method specifically includes:
acquiring attitude information of a mechanical arm clamping the grinding tool and a pressure signal of the pressure sensor in real time;
and judging the attitude position of the grinding tool assembly according to the attitude information of the mechanical arm, and calculating the pressure applied to the machined workpiece by the self gravity of the grinding tool assembly or the pressure sensor through the attitude position of the grinding tool assembly so as to determine the actual torque required to be output by the driving part.
Therefore, the posture information of the mechanical arm can be directly obtained from the inside of the controller of the robot, and the calculation efficiency is improved.
Alternatively to this, the first and second parts may,
detecting the gravity W of the grinding tool assembly by using the pressure sensor in advance, and storing the gravity W in a controller;
in the grinding process, determining an included angle theta between the normal direction and the vertical direction of the grinding position of the workpiece in the current state according to each angle sensor arranged on the mechanical arm; according to formula FFruit of Chinese wolfberry＝FApplying (a) toW cos θ determines the actual torque that the drive member needs to output.
Alternatively to this, the first and second parts may,
the grinding lower limit position range is determined by the following method: before grinding work begins, a mechanical arm drives the grinding tool to move towards a standard position of a machined workpiece, the contact pressure between the grinding tool and the machined workpiece is detected in real time in the moving process, the contact position of the machined workpiece and the grinding tool in the current state is defined as a grinding lower limit position under the condition that the contact pressure reaches a preset pressure, and then the grinding lower limit position range is determined according to the grinding lower limit position;
the standard position is the position of the surface to be ground of the workpiece to be ground after the surface to be ground is ground.
From this, drive grinding apparatus and standard position contact once through the arm and can confirm to grind the lower limit position to can accurate, confirm fast and grind the lower limit position, be favorable to follow-up grinding technology to the one-time grinding shaping of work piece, further improve grinding efficiency.
Optionally, while determining the polishing lower limit position, the encoder of the driving part feeds back the position information to the controller to record the polishing lower limit position inside the controller.
Alternatively to this, the first and second parts may,
the torque control strategy comprises a pressure increase curve prestored in a controller, and when the detected contact pressure is greater than or equal to the preset contact pressure, the contact pressure is increased to the preset grinding pressure range according to the pressure increase curve; wherein the pressure increase curve is a curve of pressure values changing along with time;
or, the torque control strategy includes a preset time period during which the contact pressure is gradually increased to the predetermined grinding pressure range when the detected contact pressure is greater than or equal to the preset contact pressure.
Therefore, the control logic can be simplified, and the machining efficiency can be improved while the pressure increase acceleration is controlled.
In addition, the invention also provides a control method of the grinding process, which comprises the following specific steps:
before the grinding process is started, executing a speed control strategy to control the speed of the grinding tool relatively approaching to the processed workpiece;
and detecting the pressure between the grinding tool and the processed workpiece and the current grinding position in real time, stopping the speed control strategy when the contact pressure between the grinding tool and the processed workpiece is judged to be less than a preset contact pressure and the current grinding position is within the grinding lower limit position range, and executing a position control strategy to keep the grinding tool or the processed workpiece within the grinding lower limit position range in the moving process of the mechanical arm.
Therefore, whether the grinding lower limit position range is reached or not is detected while the speed control strategy is carried out, and if the grinding lower limit position range is reached, the position control strategy is switched to, so that the surface of the workpiece is prevented from being over-cut.
Optionally, the following steps are further executed in the process of executing the position control strategy: and judging whether the contact pressure between the grinding tool and the processed workpiece is larger than the upper limit value of the preset grinding pressure range, if so, stopping executing the position control strategy, and executing a torque control strategy to control the output torque of the driving part so as to adjust the contact pressure between the grinding tool and the processed workpiece to the preset grinding pressure range.
In addition to the above control method, the present invention provides a polishing apparatus comprising:
a grinding tool for grinding a surface of a work piece;
the controller stores a speed control strategy, a torque control strategy and a position control strategy; the controller controls the grinding tool to grind the surface of the workpiece by adopting any one of the control methods of the grinding process.
In addition, the invention also provides a robot grinding system which is characterized by comprising the following components:
the robot is provided with a plurality of sections of mechanical arms which are connected in sequence;
the grinding device is arranged at the free end part of the last section of mechanical arm;
the controller stores a speed control strategy, a torque control strategy and a position control strategy; the controller controls the grinding device to grind the surface of the workpiece by adopting the control method of any one of the grinding processes.
Optionally, the grinding device includes a grinding tool assembly, a servo motor and a servo control system, a pressure sensor is disposed between the grinding tool assembly and the servo motor, and the controller sends a command to the servo control system to control the servo motor to operate according to the pressure detected by the pressure sensor.
The grinding device and the robot grinding system have the controller provided with the control method, so the grinding device and the robot grinding system also have the technical effects of the control method
Drawings
FIG. 1 is a schematic view of a polishing apparatus according to an embodiment of the present invention;
FIG. 2 is a flow chart of a method of controlling a polishing process in accordance with one embodiment of the present invention;
FIG. 3 is a schematic diagram illustrating contact pressures between a grinding tool and a workpiece at different locations of the workpiece during grinding of the workpiece according to an embodiment of the present invention;
FIG. 4 is a flowchart illustrating a control for determining a lower grinding limit position range according to an embodiment of the present invention;
FIG. 5 is a flow chart illustrating a process for correcting a pressure between a grinding tool and a workpiece during a grinding process according to an embodiment of the present invention;
FIG. 6 is a schematic view of the positional relationship of the abrasive tool assembly to the workpiece at a particular point in time in accordance with the present invention;
FIG. 7 is a block diagram of a control system in an embodiment of the present invention.
Wherein, the one-to-one correspondence between component names and reference numbers in fig. 1 is as follows:
the robot arm 100, the free end portion 100a, the table 200;
a servo motor 11, a screw rod 12, a nut 13 and a pressure sensor 14;
a mounting frame 20, a power component 21, a grinding tool 22, a driving pulley 23, a driven pulley 24 and a transmission belt 25;
a work piece 30.
Detailed Description
The robot grinding system utilizes a grinding tool arranged at the free end part of the robot to process and grind the surface of a product to be ground. In the product grinding process, factors influencing the quality of the formed surface of a ground product are many, such as the type of a grinding tool, the material quality of a workpiece, the grinding force and the like, wherein the grinding force is one of important factors influencing the quality of the finally ground formed surface.
As an example, the grinding force is determined mainly by: an operator selects a proper grinding force value according to the grinding precision requirement of the surface to be ground, and adjusts the proper distance position of the grinding tool on the surface to be ground by combining the operation experience, so that the pressure applied to the surface to be ground by the grinding tool approximately meets the working requirement during grinding.
Practice proves that although the robot grinding system in the above example can finish grinding the surface of the product quickly, the grinding surface precision is not uniform and sometimes greatly differs, that is, the precision of a part of the grinding surface meets the requirement, and the precision of a part of the grinding surface does not meet the requirement. Sometimes, the surface after grinding needs to be partially ground, which is labor-consuming and time-consuming.
Based on the above findings, the present invention has been made to further study and search, and has proposed a solution to the above-mentioned technical problem of large difference in the precision of the polished surface.
In order to make the technical solutions of the present invention better understood by those skilled in the art, the present invention will be further described in detail with reference to a grinding apparatus, a control method, a robot grinding system, a drawing, and specific examples.
Referring to fig. 1 and 7, fig. 1 is a schematic structural diagram of a polishing apparatus according to an embodiment of the present invention; FIG. 7 is a block diagram of a control system in an embodiment of the present invention.
The robot polishing system includes a robot having a plurality of stages of the robot arms 100, the stages of the robot arms 100 being connected in series, and a polishing device which can be attached to an end portion 100a of the last stage of the robot arm 100, the work 30 being fixed to the table 200 by a jig, for example, and the end portion 100a of the robot being moved along a predetermined path to complete polishing of the surface of the work 30. Of course, the workpiece 30 may be disposed at the end 100a of the robot, the polishing device is fixed to the worktable 200, and the robot drives the workpiece 30 to move along the predetermined path, thereby completing the polishing of the surface of the workpiece 30.
The grinding apparatus generally includes a grinder assembly including a mounting bracket 20, a power member 21, a grinder 22, a drive pulley 23, a driven pulley 24, and a drive belt 25. The grinding tool 22 is mainly used for contacting with and finishing the surface to be ground of the workpiece 30, and the suitable grinding tool 22 is selected according to the workpiece 30, and the material of the grinding tool 22 is not described in detail herein, and reference can be made to the prior art. The power unit 21 mainly provides the rotational force required for grinding the grinding tool 22, i.e., drives the grinding tool 22 to rotate. The power unit 21 may be a motor, and the power unit 21 is taken as an example to describe the technical solution, however, it should be understood by those skilled in the art that the power unit of the grinding tool herein is not limited to a motor, and may be other units as long as the power unit can provide the rotational power of the grinding tool.
Generally, the grinder 22, the power member 21, the driving pulley 23, the driven pulley 24 and the transmission belt 25 are all mounted on the mounting frame 20, wherein the driving pulley 23, the driven pulley 24 and the transmission belt 25 form a transmission member, and the power member 21 drives the grinder 22 to rotate through the driving pulley 23, the driven pulley 24 and the transmission belt 25, i.e., the power of the power member 21 is transmitted to the grinder 22 through the driving pulley 23, the driven pulley 24 and the transmission belt 25. Among them, the mounting frame 20, the driving pulley 23, the driven pulley 24 and the driving belt 25 are unnecessary components constituting the grinding tool assembly.
The grinding apparatus further includes a driving unit for mainly driving one of the grinding tool 22 and the work material 30 to move relative to the other to adjust a distance between the grinding tool 22 and the work material 30. That is, the driving unit may drive the grinding tool 22 to approach or separate from the workpiece 30, or may drive the workpiece 30 to approach or separate from the grinding tool 22, that is, change the distance between the grinding tool 22 and the surface to be ground of the workpiece 30, and accordingly change the grinding force between the grinding tool 22 and the surface to be ground.
The driving means may directly drive the grinder 22 or the workpiece 30, or may indirectly drive the grinder 22 or the workpiece 30, that is, an intermediate means is provided, and the driving means drives the intermediate means to drive the grinder 22 or the workpiece 30. The driving member may be a telescopic shaft or a servomotor 11, and in this case, it is preferable that the servomotor 11 is controlled by a servomotor drive system, and the controller controls the servomotor 11 to operate by controlling the servomotor drive system.
The invention provides a control method of a grinding process, which comprises the following specific steps:
in the initial stage of grinding, a speed control strategy is executed to control the speed of the grinding tool 22 relatively close to the processed object; and, while carrying out the speed control strategy, also detect the pressure between the grinding tool 22 and the work piece 30 in real time, judge the magnitude of the contact pressure F ' between the grinding tool 22 and the work piece 30 and the preset contact pressure F0, when the contact pressure F ' is greater than or equal to the preset contact pressure F0, stop carrying out the speed control strategy, and carry out the torque control strategy to control the output torque of the driving part to make the pressure between the grinding tool and the work piece gradually increase from the contact pressure F ' of the present state to the predetermined grinding pressure range, and maintain the contact pressure in the predetermined grinding pressure range to grind the work piece 30.
That is, referring to fig. 2, the control method may be performed according to the following flow:
s0, starting;
s1, executing a speed control strategy to control the speed of the grinding tool 22 relatively close to the processed workpiece;
s2, judging the sizes of F 'and F0, if F' is larger than or equal to F0, executing S3; otherwise, executing S1;
and S3, executing a torque control strategy to control the output torque of the driving component to gradually increase the pressure between the grinding tool and the workpiece from the contact pressure F' in the current state to a preset grinding pressure range, and maintaining the contact pressure in the preset grinding pressure range to grind the workpiece 30.
As described above, the end 100a of the last arm 100 of the robot may be the grinder 22 or the workpiece 30, that is, the robot may clamp the grinder 22 close to the workpiece 30 or clamp the workpiece 30 close to the grinder 22. For simplicity of description of the technical solution, the technical solution and the technical effects will be further described by taking the example that the grinder 22 is mounted on the end 100a of the last mechanical arm 100 of the robot.
Of course, the control methods provided herein are also applicable to a grinding system in which the work piece 30 is mounted to the robot end 100 a.
The driving component for adjusting the distance between the grinding tool 22 and the workpiece 30 may include a servo motor 11 and a nut-screw assembly, the nut-screw assembly includes a screw 12 and a nut 13, the grinding tool assembly is mounted on the screw 12, the servo motor 11 drives the nut 13 to rotate, and then the screw 12 is driven to move back and forth, so that the grinding tool 22 assembly is close to or far away from the workpiece 30. Of course, the drive components are not limited to the servomotor 11 and nut screw assembly described herein above, so long as relative movement of the grinding tool 22 with respect to the work piece 30 is achieved.
The pressure between the grinding tool 22 and the workpiece 30 can be detected by the pressure sensor 14.
The predetermined grinding pressure range may be a specific value in theory, but the predetermined grinding pressure range may be a range of values in general, in consideration of the machining accuracy, machining efficiency, and other factors of the workpiece. The predetermined grinding pressure range may be determined by the predetermined grinding pressure F1 input to the controller. The magnitude of the preset contact pressure may be appropriately selected depending on the material of the work 30 and the material of the grinding tool 22. The preset contact pressure F0 and the predetermined grinding pressure range are stored in the controller before the grinding process is performed. For convenience of operation, the preset contact pressure F0 and the predetermined grinding pressure F1 may be input to the controller by the touch panel. The signal input port of the controller is connected with the signal output port of the pressure sensor 14, and the controller can receive the detection signal from the pressure sensor 14, and determine the specific value of the pressure between the grinding tool 22 and the workpiece 30 at this time through the detection signal.
As can be seen from the above description, the preset contact pressure F0 is smaller than a specific value in the predetermined grinding pressure range. Two control strategies are set in the control method of the invention: and a speed control strategy and a torque control strategy, wherein in the process of grinding contact between the grinding tool 22 and the workpiece 30, before the pressure between the grinding tool 22 and the workpiece 30 does not reach the preset contact pressure F0, the speed control strategy is executed, the grinding tool 22 is controlled to approach the workpiece 30 at a preset speed, and when the pressure between the grinding tool 22 and the workpiece 30 is detected to be greater than or equal to the preset contact pressure F0, the speed control strategy is switched to the torque control strategy, so that the pressure between the grinding tool 22 and the workpiece 30 is slowly increased to a preset grinding pressure range. That is, the movement of the grinding tool 22 relative to the work piece 30 is divided into two stages: the first stage is to control the moving speed of the grinding tool 22 by the speed control strategy until the contact pressure F' between the grinding tool 22 and the workpiece 30 is increased to the preset contact pressure F0, the second stage is to control the grinding tool 22 to move relative to the workpiece 30 by the torque control strategy until the pressure between the grinding tool 22 and the workpiece 30 is increased to the preset grinding pressure range from the preset contact pressure F0, the first stage can control the grinding tool 22 to move to the workpiece 30 at the preset speed by the speed control strategy, the contact impact between the grinding tool 22 and the workpiece 30 can be relieved, and the second stage is to easily and accurately control the pressure increasing speed between the grinding tool 22 and the workpiece 30, and the pressure is prevented from increasing too fast to exceed the preset grinding pressure range.
According to the control method provided by the invention, a good force buffering effect can be achieved through a speed control strategy, so that the grinding tool 22 can be well protected, the service life of the grinding tool 22 is prolonged, and the surface processing precision of the processed workpiece 30 is improved.
The pressure between the grinding tool 22 and the workpiece 30 gradually increasing from the preset contact pressure F0 to the preset grinding pressure range may be increased according to the following manner: increasing the preset contact pressure F0 to a preset grinding pressure range according to a pressure increase curve prestored in the controller; that is, the torque control strategy includes a pressure increase curve that is pre-stored within the controller. The pressure increase curve is a curve of the pressure value changing along with time, so that the preset contact pressure can be increased according to a preset speed in the process of increasing to a preset grinding pressure range, Overshoot (Overshoot) caused by too fast increase is relieved, and the grinding surface precision can be further improved.
The torque control strategy may also include a preset time period during which the contact pressure is gradually increased to the predetermined grinding pressure range when the detected contact pressure is greater than or equal to the preset contact pressure. The longer the preset time period, the smaller the acceleration of the speed increase, and the Overshoot (Overshoot) caused by the speed surge is alleviated. Namely, the speed increase acceleration is controlled, which is beneficial to improving the quality of the grinding surface.
Maintaining the pressure between the grinding tool 22 and the workpiece 30 within a predetermined grinding pressure range, i.e. a is less than or equal to FWhen in useB is not more than b, a is the minimum value of the preset grinding pressure range, b is the maximum value of the preset grinding pressure range, FWhen in useThe pressure between the grinding tool 22 and the workpiece 30 is the current state. It should be noted that a and b herein may not be equal; a and b may also be equal.
Therefore, the grinding surface of the workpiece 30 to be processed is roughly under the same grinding force for grinding, the surface precision after grinding is basically the same, the overall quality of the grinding surface of the workpiece 30 to be processed is greatly improved, the qualified rate of grinding products is improved, and the production efficiency is further improved.
While executing the torque control strategy to grind the workpiece, the following steps are also carried out: and detecting the current grinding position in real time, judging whether the current grinding position reaches the grinding lower limit position range, if so, stopping executing the torque control strategy, and executing the position control strategy to keep the grinding tool 22 or the processed workpiece 30 in the grinding lower limit position range in the moving process of the mechanical arm 100.
That is, when it is detected that the position of the grinder 22 reaches the grinding lower limit position range during execution of the torque control strategy, the grinder 22 is held at the position and the robot arm 100 continues to move along the predetermined path. At this time, the contact pressure between the grinder 22 and the work material 30 is less than the minimum value of the predetermined grinding pressure range. That is, when it is detected that the position of the grinder 22 reaches the grinding lower limit position range, the position of the grinder 22 is controlled by switching from the torque control strategy to the position control strategy.
The following steps are also executed simultaneously in the process of executing the position control strategy: and judging whether the contact pressure between the grinding tool 22 and the workpiece 30 is larger than the upper limit value a of the preset grinding pressure range, if so, stopping executing the position control strategy, and executing the torque control strategy to control the output torque of the driving part so as to adjust the contact pressure between the grinding tool 22 and the workpiece 30 to the preset grinding pressure range.
That is, when the position control strategy is executed, if the detected contact pressure between the grinder 22 and the workpiece 30 is greater than a, the position control strategy is switched to the torque control strategy, the drive motor 11 drives the nut 13 to rotate, the vertical position of the screw 11 is adjusted, the position of the grinder 22 is adjusted, the contact pressure between the grinder 22 and the workpiece 30 is adjusted to a predetermined grinding pressure range, and the surface of the workpiece 30 is ground with a constant grinding force.
Referring to fig. 3, fig. 3 is a schematic view illustrating a contact pressure between a grinding tool and a workpiece at different positions of the workpiece when the workpiece is ground according to an embodiment of the present invention; the control method is shown in fig. 3 only for a part of the time period during which grinding is started. In fig. 3, the abscissa represents time and the ordinate represents force.
The above control method is specifically described herein by taking the example of grinding a planar weld with different concave-convex portions.
As shown in fig. 3, the surface of the workpiece 30 is uneven, and the grinding process specifically includes:
initial 0 to t1 stage of grinding: the execution speed control strategy controls the driving motor 11 to rotate, and the screw rod 12 drives the grinding tool 22 to move towards the processed workpiece 30 at a certain speed.
Stage t1 to t 2: when the grinding tool 22 moves to the position a, the contact pressure between the grinding tool 22 and the workpiece 30 reaches F0, the control strategy of the driving component is switched to the torque control strategy, the contact pressure between the grinding tool 22 and the workpiece 30 is gradually increased from F0 to F1 according to the torque control strategy, and the contact pressure between the two is maintained in the preset grinding pressure range.
Stage t2 to t 3: when the grinder 22 moves to the position B and the grinder 22 reaches the grinding lower limit position range (where P1 is the grinding lower limit position), the position control strategy is switched to maintain the grinder 22 in the grinding lower limit position range during the movement of the robot arm.
Stage t3 to t 4: when the grinding tool 22 exceeds the position C, the contact pressure between the grinding tool 22 and the workpiece 30 is greater than F1, the position control strategy is switched to the torque control strategy, and the servo motor 11 drives the screw rod 12 to move upwards to adjust the contact pressure between the grinding tool 22 and the workpiece 30 to be F1.
The polishing control in the subsequent time period can be referred to the above description, and is not repeated herein.
The above description is only made in detail by taking the control method applied to the polishing of a flat surface as an example, but it is needless to say that the control method provided by the present invention is not limited to flat surface polishing, and can also be applied to curved surfaces, inclined surfaces, and the like, and the polishing control principle is the same, and will not be described in detail herein.
The control method of the grinding process provided by the invention is provided with three control strategies, namely a speed control strategy, a torque control strategy and a position control strategy, and selects corresponding control strategies according to different conditions when the surface of the processed workpiece 30 is ground, so that the grinding tool is greatly prevented from being damaged by overlarge grinding force and the grinding surface precision is reduced in the process that the grinding tool transversely moves along a preset track along a mechanical arm, and the service life of the grinding tool and the grinding surface precision are improved.
Referring to fig. 4, fig. 4 is a control flow chart illustrating the determination of the polishing lower limit position range according to an embodiment of the present invention.
The polishing lower limit position range in the above embodiment may be a specific position or may be a single position range. The determination can be specifically determined by the following method: the lower grinding limit position is determined by: before the grinding operation starts, the mechanical arm 100 drives the grinding tool 22 to move towards the standard position of the workpiece 30, and detects the contact pressure between the grinding tool 22 and the workpiece 30 in real time during the movement, and defines the contact position between the workpiece 22 and the current state as the grinding lower limit position under the condition that the contact pressure reaches the predetermined pressure. Before the grinding work is started, the following steps are carried out:
s01, the mechanical arm drives the grinding tool 22 to move towards the standard position of the processed workpiece 30, and the contact pressure between the grinding tool 22 and the processed workpiece 30 is detected in real time in the moving process;
s02, judging the contact pressure between the grinding tool 22 and the machined workpiece 30 in the current state and the preset pressure; when the contact pressure is greater than or equal to the predetermined pressure, step S03 is executed; otherwise, continuing to execute step S01;
s03, defining the contact position of the workpiece to be machined 30 and the grinding tool 22 in the current state as a grinding lower limit position, and further determining a grinding lower limit position range according to the grinding lower limit position;
the polishing lower limit position is a specific position, and may be set to a range, i.e., a polishing lower limit position range, according to the polishing lower limit position, in consideration of control efficiency, machining efficiency, and the like. While determining the polishing lower limit position, the encoder of the drive member feeds back the position information to the controller to record the polishing lower limit position inside the controller.
The standard position is the position of the surface to be ground of the workpiece to be ground, which is to be formed after the surface to be ground is ground.
Before the grinding process is carried out, the grinding tool is driven by the mechanical arm to contact the standard position once, so that the grinding lower limit position can be determined, the grinding lower limit position can be accurately and quickly determined, the subsequent grinding process is facilitated to grind and form a machined workpiece once, and the grinding efficiency is further improved.
The pressure sensor may not be directly attached to the contact surface of the grinding tool 22 and the work material 30 in consideration of the quality of grinding of the work material 30 and the life of the pressure sensor. As can be seen from fig. 1, a pressure sensor for detecting a pressure between the grinding tool 22 and the workpiece 30 in the grinding apparatus is generally provided between the driving member and the grinding tool 22 assembly. When the grinding tool 22 is in a different attitude, the pressure value actually detected by the pressure sensor 14 may not be the same as the actual contact pressure between the grinding tool 22 and the work material 30. That is, the feedback value of the pressure sensor 14 is not the actual pressure value between the grinding tool 22 and the workpiece 30. In order to compensate for the accuracy of the pressure value detected by the pressure sensor 14, the control method of the present invention further corrects the detected pressure before the determining step: the detected pressure is corrected in consideration of the self-weight factor of the grinder assembly. The posture of the grinding tool assembly can be judged in various modes, and an angle sensor can be arranged on the grinding tool assembly to judge the posture of the grinding tool assembly at the moment. For a robot system, a sensor for detecting motion displacement of the robot arm 100 is usually disposed on the robot arm 100 of the robot, so that the correction of the pressure signal in the method of the present invention is specifically performed according to the following method, please refer to fig. 5, which includes the following specific steps:
s001, acquiring attitude information of a mechanical arm for clamping the grinding tool 22 and a pressure signal of a pressure sensor in real time; and S002, judging the attitude position of the grinding tool assembly according to the attitude information of the mechanical arm, calculating the pressure applied to the machined workpiece by the gravity of the grinding tool assembly or the pressure of the pressure sensor through the attitude position of the grinding tool assembly, and further determining the actual torque required to be output by the driving part.
Specifically, each section of the mechanical arm 100 is provided with an angle sensor, and the controller can determine the posture of the grinder assembly in the current state according to a signal detected by the angle sensor. Alternatively, the acquisition of the posture information of the robot arm 100 may be directly read from the inside of a controller that controls the robot, thereby improving the calculation efficiency.
As described above, the pressure sensor is installed between the grinder assembly and the driving part, and before grinding starts, the grinder assembly may be in a vertical state, and the gravity W of the grinder assembly may be detected by the pressure sensor and stored in the controller.
In the grinding process, determining an included angle theta between the normal direction and the vertical direction of the grinding position of the workpiece in the current state according to each angle sensor arranged on the mechanical arm; according to formula FFruit of Chinese wolfberry＝FApplying (a) toW cos θ determines the actual torque that the drive member needs to output. Referring to FIG. 6, FIG. 6 shows the position of the grinder assembly in an embodiment where the actual pressure F between the grinder 22 and the workpiece 30 isFruit of Chinese wolfberry＝FApplying (a) to+W*cosθ。
Wherein, FFruit of Chinese wolfberryActual output torque for the drive member; fApplying (a) toIs the pressure detected by the pressure sensor; theta is an included angle between the normal direction of the contact position of the grinding tool and the workpiece and the vertical direction.
The method for correcting the pressure between the grinding tool and the machined workpiece fully considers the influence of the gravity of the grinding tool assembly at different positions on the pressure signal detected by the pressure sensor, obtains the actual pressure between the grinding tool 22 and the machined workpiece 30, and calculates the actual torque required to be output by the driving part. This is advantageous for achieving the purpose that the surface of the workpiece 30 is ground by the grinding tool 22 with equal grinding force, improving the consistency of the ground surface precision of the workpiece, and improving the grinding efficiency.
In addition, the invention also provides a control method of the grinding process, which comprises the following specific steps:
before the grinding process is started, executing a speed control strategy to control the speed of the grinding tool relatively approaching to the processed workpiece;
and detecting the pressure between the grinding tool 22 and the processed workpiece 30 and the current grinding position in real time, stopping the speed control strategy when the contact pressure between the grinding tool 22 and the processed workpiece 30 is judged to be less than the preset contact pressure and the current grinding position is within the grinding lower limit position range, and executing the position control strategy to keep the grinding tool 22 or the processed workpiece 30 within the grinding lower limit position range in the moving process of the mechanical arm.
Further, the following steps are also executed in the process of executing the position control strategy: and judging whether the contact pressure between the grinding tool 22 and the workpiece 30 is larger than the upper limit value of the preset grinding pressure range, if so, stopping executing the position control strategy, and executing the torque control strategy to control the output torque of the driving part so as to adjust the contact pressure between the grinding tool and the workpiece to the preset grinding pressure range.
The control method considers the situation that the initial grinding position is lower than the grinding lower limit position, and is beneficial to avoiding the excessive grinding phenomenon.
In addition to the control method, the invention also provides a grinding device and a robot grinding system, wherein the grinding device and the robot grinding system are provided with a controller provided with the control method, namely a speed control strategy, a torque control strategy and a position control strategy are stored in the controller; the controller can control the grinding tool to grind the surface of the workpiece by adopting the control method of any one of the grinding processes.
The grinding device and the robot grinding system also have the technical effects of the control method.
The control method of the grinding process, the grinding device and the robot grinding system provided by the invention are described in detail above. The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
Claims (12)
1. A control method of a grinding process is characterized by comprising the following specific steps:
in the initial stage of grinding, speed control is executed to control the speed of the grinding tool relatively approaching to the processed workpiece;
detecting the pressure between the grinding tool and the processed workpiece, judging the pressure between the grinding tool and the processed workpiece and the magnitude of a preset contact pressure, stopping executing the speed control when the detected pressure is greater than or equal to the preset contact pressure, executing torque control to control the output torque of a driving part to enable the pressure between the grinding tool and the processed workpiece to be changed from the contact pressure in the current state to a preset grinding pressure range, and maintaining the pressure to be in the preset grinding pressure range to grind the processed workpiece;
the torque control comprises a pressure increase curve prestored in a controller, and when the detected pressure is greater than or equal to the preset contact pressure, the pressure is increased to the preset grinding pressure range according to the pressure increase curve; wherein the pressure increase curve is a curve of pressure values changing along with time;
alternatively, the torque control includes a preset time period during which the pressure is gradually increased to the predetermined grinding pressure range when the detected pressure is greater than or equal to the preset contact pressure.
2. The method of controlling a grinding process according to claim 1, wherein the torque control is performed to grind the work piece, and at the same time, the following steps are performed: and detecting the current grinding position, judging whether the current grinding position reaches the grinding lower limit position range, if so, stopping executing the torque control, and executing a position control strategy to keep the grinding tool or the processed workpiece in the grinding lower limit position range in the moving process of the mechanical arm.
3. The method of claim 2, wherein the following steps are further performed in performing the position control strategy: and judging whether the pressure between the grinding tool and the processed workpiece is larger than the upper limit value of the preset grinding pressure range, if so, stopping executing the position control, and executing the torque control to control the output torque of the driving part so as to adjust the pressure between the grinding tool and the processed workpiece to the preset grinding pressure range.
4. The method of controlling a grinding process according to claim 1, wherein a pressure sensor for detecting a pressure between the grinding tool and the work material is provided between the driving part and a grinding tool assembly including a grinding tool; the control method also corrects the detected pressure, and the specific correction method comprises the following steps: and correcting the detected pressure by considering the self gravity factor of the grinding tool assembly so as to determine the actual torque required to be output by the driving part.
5. The method of claim 4, wherein the modifying method specifically comprises:
acquiring attitude information of a mechanical arm clamping the grinding tool and a pressure signal of the pressure sensor;
and judging the attitude position of the grinding tool assembly according to the attitude information of the mechanical arm, and calculating the pressure applied to the machined workpiece by the self gravity of the grinding tool assembly or the pressure sensor through the attitude position of the grinding tool assembly so as to determine the actual torque required to be output by the driving part.
6. The method of controlling a grinding process according to claim 5, wherein the gravity W of the grinder assembly is detected in advance using the pressure sensor and stored in a controller;
in the grinding process, determining an included angle theta between the normal direction and the vertical direction of the grinding position of the workpiece in the current state according to an angle sensor arranged on the mechanical arm; according to formula FFruit of Chinese wolfberry＝FApplying (a) toW cos θ determines the actual torque that the drive member needs to output.
7. The method of controlling a polishing process according to any one of claims 2 to 3, wherein the polishing lower limit position range is determined by: before grinding work begins, a mechanical arm drives the grinding tool to move towards a standard position of a machined workpiece, pressure between the grinding tool and the machined workpiece is detected in the moving process, the contact position of the machined workpiece and the grinding tool in the current state is defined as a grinding lower limit position under the condition that the pressure reaches a preset pressure, and then the grinding lower limit position range is determined according to the grinding lower limit position;
the standard position is the position of the surface to be ground of the workpiece to be ground after the surface to be ground is ground.
8. The method of claim 7, wherein the encoder of the driving part feeds back the position information to a controller to record the polishing lower limit position inside the controller while determining the polishing lower limit position.
9. A grinding apparatus comprising the following components:
a grinding tool for grinding a surface of a work piece;
a controller capable of performing speed control, torque control, and position control; the controller controls the grinding tool to grind the surface of the workpiece by using the control method of the grinding process according to any one of claims 1 to 8.
10. The grinding apparatus of claim 9, wherein the grinding apparatus includes a grinder assembly, a servo motor, and a servo control system, a pressure sensor is disposed between the grinder assembly and the servo motor, and the controller sends a command to the servo control system to control the servo motor according to the pressure detected by the pressure sensor.
11. A robotic lapping system comprising the following components:
the robot is provided with a plurality of sections of mechanical arms which are connected in sequence;
the grinding device is arranged at the free end part of the last section of mechanical arm;
a controller capable of performing speed control, torque control, and position control; the controller controls the grinding device to grind the surface of the workpiece by using the control method of the grinding process according to any one of claims 1 to 8.
12. The robotic grinding system of claim 11 wherein said grinding means includes a grinder assembly, a servo motor, and a servo control system, a pressure sensor being disposed between said grinder assembly and said servo motor, said controller sending commands to said servo control system to control the operation of said servo motor based on the pressure sensed by said pressure sensor.
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| CN112658808B (en) * | 2020-11-11 | 2022-07-29 | 哈尔滨工业大学（深圳） | Force position coupling compliant polishing control method and compliant polishing control system |
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| CN105014521A (en) * | 2015-05-27 | 2015-11-04 | 苏州德锐朗智能科技有限公司 | Three-stage upper plate rising and falling speed control method for plane grinding machine |
| CN105643399B (en) * | 2015-12-29 | 2018-06-26 | 沈阳理工大学 | The complex-curved automatic grinding-polishing system of robot and processing method based on Shared control |
| CN205325472U (en) * | 2016-02-04 | 2016-06-22 | 株式会社安川电机 | Grinder and robot that has this grinder grind system |
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