CN110315571A - A kind of software actuator control method of robotic asssembly posture correction - Google Patents

Abstract

A kind of software actuator control method of robotic asssembly posture correction deflects the deformation of the method expression software actuator of direction vector and deflection angle using a kind of combination for the pneumatic software actuator of multi-chamber that can be deflected to any direction；Assembly posture correction control process is divided into assembly posture perception and assembly two stages of pose adjustment: assembly posture perception stage and assembly pose adjustment stage by the characteristics of according to pneumatic software actuator pressure control and flexible deformation.The present invention realizes the assembly posture perception and assembly posture correction during the non-rigid part robotic asssembly of isomery.

Description

A software actuator control method for robot assembly attitude correction

technical field

The invention relates to a software actuator control method, in particular to a software actuator control method for rectifying robot assembly posture.

Background technique

For heterogeneous non-rigid parts that widely exist in low-voltage electrical appliances, plastic toys, and 3C products, the contact force during the assembly process of such parts and the coordination between parts are complicated. In the automatic assembly of such parts, traditional The assembly action of clamping-positioning-installation performed by the rigid end effector usually causes parts to be damaged due to the manufacturing error, positioning error and excessive rigidity of the assembly execution system. In the current field of robotic automated assembly, in order to ensure the effective assembly of such heterogeneous non-rigid parts, rigid end grippers are often used for parts clamping. A force feedback sensor is installed at the end joint of the robot, and the assembly attitude of the part is sensed through the assembly contact force feedback, and then the assembly robot is controlled to adjust the assembly attitude according to the sensed part assembly attitude. This type of robot assembly attitude correction control method requires additional installation of force sensors, and a specific assembly attitude correction algorithm needs to be added to the robot operation control program, which increases the cost and reduces the adaptability of the attitude correction method to different robots. Operational efficiency of robotic automated assembly.

Compared with the rigid clamping mechanism, the pneumatic soft actuator made of rubber material has the characteristics of multiple degrees of freedom and high adaptability to the complex force environment, which makes the pneumatic soft actuator very good for the correction of assembly posture. potential. However, the current deformation control of the elastic-pneumatic soft body only controls the large deformation in a single deformation direction, and is not suitable for the situation of multiple deformation directions and small deformation when the assembly posture is corrected.

SUMMARY OF THE INVENTION

In order to overcome the shortcomings of high hardware cost and poor adaptability of the existing assembly attitude correction control method, the present invention proposes a software actuator control method for robot assembly attitude correction, which realizes the assembly of heterogeneous non-rigid parts in the robot assembly process. Attitude perception and assembly attitude correction.

The technical scheme adopted by the present invention to solve its technical problems is:

A software actuator control method for robot assembly attitude correction. For a multi-chamber pneumatic soft actuator that can deflect in any direction, a method combining a deflection direction vector and a deflection angle is used to represent the deformation of the soft actuator. ;According to the characteristics of air pressure control and elastic deformation of the pneumatic software actuator, the assembly attitude correction control process is divided into two stages: assembly attitude perception and assembly attitude adjustment:

In the assembly attitude perception stage, the pneumatic soft robot is regarded as a bending deformation sensor. According to the air pressure value of each chamber, the deflection direction vector of the soft body deformation can be obtained, and the soft body deformation process can be calculated according to the air pressure value feedback of each chamber and the ideal gas state equation. The volume change of , and then calculate the bending angle under the current volume change according to the curvature continuity criterion of elastic material deformation;

In the assembly posture adjustment stage, the multi-chamber software is regarded as a pneumatic bending actuator. According to the Yeoh constitutive model of the elastic body and the principle of virtual work, the relationship between the air pressure work and the bending angle can be obtained. Bend in the specified direction and at the specified angle, so as to realize the assembly posture correction.

Further, for a soft body actuator with n chambers, the soft body actuator control method includes the following steps:

Step 1: Determine the bending direction vector of each chamber of the soft actuator

Select the bottom section of the soft actuator as the projection reference plane, select the bottom center point of the soft actuator as the origin, and establish a plane coordinate system on the projection reference plane to make the control air pressure of each chamber of the pneumatic soft actuator equal, and then increase The control air pressure of the ith (1~n) chamber of the soft actuator causes the soft actuator to bend, and the unit vector of the axis of the pneumatic actuator in the projection direction of the projection datum plane as the bending direction vector of the i-th chamber;

Step 2: Collect the air pressure changes of each chamber in the standard assembly process

In the process of completing the standard assembly of the robot, the air pressure data P _i,j of each chamber of the n·k groups of soft actuators are collected at the same time interval, where i=1～n represents the different chambers of the soft actuator, j =1～k represents the serial number of the air pressure value of each chamber collected when performing the assembly action;

Step 3: Evaluate assembly deviation

When the robot performs the assembly task, the air pressure feedback values P' _i,j at different times of the ith chamber of the soft actuator are collected at the same interval as in step 1, and the difference between P _i,j and P' _i,j is compared.

|P _i,j -P' _i,j |>δ (1)

Then it is considered that there is an error in the assembly process, the current air pressure value P' _i of each chamber is recorded and the robot is notified to stop the assembly action and return to a safe position, where δ is the set allowable error range;

Step 4: Soft Body Pose Perception When Assembly Errors Occur

When there is an error in the assembly process, the soft actuator will bend under the action of external force, and its bending direction is the direction of the external force. The resultant force of the software brake is reversed; according to the bending direction vector of each chamber determined in step 1 and the air pressure value P' _i of each chamber under the bending condition, the bending of the resultant force of the software actuator by the air pressure of each chamber under the error condition can be obtained The direction vector is

Then the bending direction of the soft actuator under the error condition is opposite to this direction vector, that is,

Assuming the bending deformation process of the soft body actuator under the condition of assembly error to simplify the analysis, according to the ideal gas state equation, the relationship between the gas volume V and the pressure P is:

where n is the amount of gas substance, R is the gas constant, and T is the temperature. According to the cavity volume and air pressure before the bending deformation of the soft body actuator, the air pressure value after the bending deformation and the formula (4), the soft body actuator after the deformation is obtained. Actuator air cavity volume V _m ;

Further, according to the cross-sectional shape of the soft actuator, the relationship between the bending angle θ after the bending deformation and the volume V _m of the soft actuator is obtained

θ=f(V _m ) (5)

Then, according to the bending direction of the soft actuator provided by the formula (3) and the bending angle provided by the formula (5), the assembly posture of the soft actuator when the assembly error is determined;

Step 5: Adjustment of the assembly attitude of the software actuator

According to the contact force in the part assembly process, the analysis of the fit type, and the perception of the assembly attitude during the assembly deviation in step (4), the correct assembly attitude under the current error condition is obtained, that is, the deflection direction vector of the software actuator when the correct assembly is performed. and the deflection angle θ _c ;

The bending direction vector of each chamber air pressure to the resultant force of the soft body actuator expressed in formula (2), then we have

where P _in,i is the input gas pressure of each air cavity;

Based on the assumption in step 4 and formula (5), the volume of each air cavity is obtained when the bending angle of the soft actuator is _θc

V _m,i = _gi (θ _c )(i=1～n) (7)

where n is the number of air cavities of the soft actuator, g _i () is the functional relationship between the bending angle θ _c and the volume V _m,i of each air cavity;

In the process of adjusting the assembly attitude of the soft actuator, the work done by the compressed gas is completely used to overcome the external restraint force and the work done by the internal stress of the rubber material. According to the principle of virtual work, a balance expression is established.

Among them, dV _c,i is the volume change of the air cavity before and after attitude adjustment, V _{r, i} is the volume of the rubber material in each air cavity, W _ou is the work done to overcome the external constraints, W is the energy density function of the rubber material, using the second-order Yeoh The constitutive model strain energy density function, then

Among them, C ₁₀ and C ₂₀ are material parameters, and λ is the axial main elongation ratio of the actuator;

Simultaneous formulas (6) to (9) are substituted into the known quantities of each part to obtain the input gas pressure P _in,i of each air cavity required for the attitude correction control of the software actuator, and the required value is achieved by controlling the input gas pressure, namely Adjust the pneumatic software actuator to the correct assembly posture, and return to step 3 to perform the assembly action again.

In the fourth step, for the bending deformation process of the soft actuator under the condition of assembly error, the following assumptions are made to simplify the analysis:

4.1) There is no radial expansion of the pneumatic software actuator, that is, the outer contour size of the section remains unchanged;

4.2) The rubber material on the outer wall of the air cavity of the pneumatic software actuator changes uniformly;

4.3) The mechanical influence of the strain limiting layer on the overall deformation process is not considered;

4.4) The overall volume of the elastic matrix remains unchanged before and after deformation;

4.5) The curvature of the multi-chamber pneumatic soft actuator changes uniformly during the bending deformation process.

The main technical idea of the present invention is as follows: a projection method is used to express the bending direction of the pneumatic soft actuator as the action direction of the combined pressure of each air cavity, and the automatic assembly process of the robot is realized by using the air pressure feedback of each air cavity of the pneumatic soft actuator. Through the air pressure control of the software actuator, the pneumatic software can be bent and deformed in a specified way to achieve the purpose of rectifying and adjusting the assembly posture.

The beneficial effects of the present invention are mainly manifested in that a software actuator control method applied to robot assembly posture correction is proposed, which can reduce hardware cost and improve robot assembly of heterogeneous non-rigid parts compared with other assembly posture recognition and correction. efficiency and applicability.

Description of drawings

FIG. 1 is a flowchart of a software actuator control method for robot assembly posture correction.

Figure 2 shows an example of a soft pneumatic actuator application.

Fig. 3 is the A-A sectional view of Fig. 2, wherein 1 is the end effector base plate, 2 is the movable top ball mounting rod, 3 is the top ball mounting rod, 4 is the three-chamber cylindrical pneumatic software device, and 5 is the clamping mechanism installation Rod, 6 is the fixed top ball, 7 is the top-tightening cylinder, 8 is the cylinder mounting plate, 9 is the top ball spring, 10 is the fixing plate of the clamping mechanism, and 11 is the clamping mechanism.

Figure 4 is a schematic diagram of the deflection of the soft pneumatic actuator.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

Referring to Figures 1 to 4, a software actuator control method for robot assembly posture correction, for multi-chamber pneumatic soft actuators that can deflect in any direction, a method combining deflection direction vector and deflection angle is used to represent Deformation of soft body actuators. According to the characteristics of air pressure control and elastic deformation of the pneumatic software actuator, the assembly attitude correction control process is divided into two stages: assembly attitude perception and assembly attitude adjustment. In the assembly attitude perception stage, the pneumatic soft robot is regarded as a bending deformation sensor. According to the air pressure value of each chamber, the deflection direction vector of the soft body deformation can be obtained, and the soft body deformation process can be calculated according to the air pressure value feedback of each chamber and the ideal gas state equation. The volume change of , and then calculate the bending angle under the current volume change according to the curvature continuity criterion of elastic material deformation. In the assembly attitude adjustment stage, the multi-chamber software is regarded as a pneumatic bending actuator. According to the Yeoh constitutive model of the elastic body and the principle of virtual work, the relationship between the air pressure work and the bending angle can be obtained. The software body is bent in the specified direction and at the specified angle, so as to realize the correction of the assembly posture.

The present invention is further described with a rigid-soft composite robot end-effector using a three-chamber soft-body pneumatic actuator (part 4 in FIG. 2 ) as an object, and the soft-body actuator control method includes the following steps:

Step 1: Determine the bending direction vector of each chamber of the soft actuator

Select the bottom section of the soft actuator as the projection datum, select the bottom center point of the soft actuator as the origin, and establish a plane coordinate system on the projection datum. Make the control air pressure of each chamber of the pneumatic soft actuator equal, and then increase the control air pressure of a chamber of the soft actuator to bend the soft actuator (as shown in Figure 3). Each air cavity of the actuator is arranged at an interval of 120°, and the unit vector of each air cavity on the projection datum plane respectively (As shown in Figure 3).

Step 2: Collect the air pressure changes of each chamber in the standard assembly process

In the process of completing the standard assembly of the robot, the air pressure data P _i,j of each chamber of the n·k groups of soft actuators are collected at the same time interval. Wherein i=1-3 represent different chambers of the soft actuator, and j=1-k represent the serial numbers of the air pressure values of the chambers collected when performing the assembly action.

Step 3: Evaluate assembly deviation

When the robot performs the assembly task, the air pressure feedback values P' _i,j at different times of the ith chamber of the soft actuator are collected at the same time interval as in step 1, and the difference between P _i,j and P' _i,j is compared.

|P _i,j -P' _I,j |>0.1Pa (1)

Then it is considered that there is an error in the assembly process, the current air pressure value P' _i of each chamber is recorded and the robot is notified to stop the assembly action and return to a safe position.

Step 4: Soft Body Pose Perception When Assembly Errors Occur

When an error occurs in the assembly process, the soft actuator bends under the action of external force (as shown in Figure 3), and its bending direction is the direction of the action of the external force. The external force is opposite to the resultant force of the air pressure of each chamber on the soft brake. According to the bending direction vector of each chamber determined in step 1 and the air pressure value P _i of each chamber under the bending condition, the bending direction vector of each chamber air pressure to the resultant force of the soft actuator under the error condition can be obtained as:

Then the bending direction of the soft actuator under the error condition is opposite to this direction vector, that is,

For the bending deformation process of the soft-body actuator under the condition of assembly error, the following assumptions can be made to simplify the analysis:

4.1) There is no radial expansion of the pneumatic software actuator, that is, the outer contour size of the section remains unchanged;

4.2) The rubber material on the outer wall of the air cavity of the pneumatic software actuator changes uniformly;

4.3) The mechanical influence of the strain limiting layer on the overall deformation process is not considered;

4.4) The overall volume of the elastic matrix remains unchanged before and after deformation;

4.5) The curvature of the multi-chamber pneumatic soft actuator changes uniformly during the bending deformation process.

Based on the above assumptions, according to the ideal gas equation of state, the relationship between the gas volume V and the gas pressure P is

where n is the amount of gas substance, R is the gas constant, and T is the temperature. Then, the air cavity volume V _m of the soft actuator after the deformation can be obtained according to the cavity volume and air pressure before the bending deformation of the soft actuator, the air pressure value after the bending deformation and the formula (4). Further, based on the above assumptions 4.1), 4.4), 4.5) according to the cross-sectional shape of the soft actuator, the relationship between the bending angle θ after the bending deformation and the volume V _m of the soft actuator is obtained

θ=f(V _m ) (5)

Then, according to the bending direction of the soft actuator provided by the formula (3) and the bending angle provided by the formula (5), the assembly posture of the soft actuator during the assembly error can be determined.

Step 5: Adjustment of the assembly attitude of the software actuator

According to the contact force in the part assembly process, the analysis of the fit type and the perception of the assembly attitude during the assembly deviation in step (4), the correct assembly attitude under the current error condition can be obtained, that is, the deflection direction vector of the soft actuator during correct assembly. and the deflection angle θ _c .

The bending direction vector of each chamber air pressure to the resultant force of the soft actuator expressed in formula (2), then we have

where P _in,i is the input gas pressure of each air cavity.

Based on the assumptions 4.1)～4.5) and formula (5) in step 4, the volume of each air cavity can be obtained when the bending angle of the soft actuator is _θc

V _m,i = _gi (θ _c )(i=1～3) (7)

where g _i () is the functional relationship between the bending angle θ _c and the volume V _m,i of each air cavity;

In the process of adjusting the assembly attitude of the soft actuator, the work done by the compressed gas is completely used to overcome the external restraint force and the work done by the internal stress of the rubber material. According to the principle of virtual work, a balance expression is established.

Among them, dV _c,i is the volume change of the air cavity before and after attitude adjustment, V _{r, i} is the volume of the rubber material in each air cavity, W _ou is the work done to overcome the external constraints, W is the energy density function of the rubber material, using the second-order Yeoh The constitutive model strain energy density function, then

Among them, C ₁₀ and C ₂₀ are material parameters, and C ₁₀ =0.11MPa and C ₂₀ =0.02MPa are taken from the rubber material, and λ is the axial main elongation ratio of the actuator.

In the applied example, the three-air-chamber pneumatic actuator is fixed on the clamp mounting rod, and the fixed clamp mounting rod is constrained by the spring force (as shown in Figure 2), so during the attitude adjustment process Have

Among them, m is the number of springs, k _i , _li are the spring coefficients of each tensioning spring and the deformation amount during attitude adjustment, respectively, G and h are the weight of the object fixed on the soft actuator and its attitude Displacement during adjustment.

Simultaneous formulas (6) to (10) are substituted into the known quantities of each part to obtain the input gas pressure P _in,i of each air cavity required for the attitude correction control of the software actuator, and the required value is achieved by controlling the input gas pressure, namely Adjustable pneumatic soft body actuator to the correct assembly posture.

Claims (3)

1. a kind of software actuator control method of robotic asssembly posture correction, which is characterized in that for can be to any direction The pneumatic software actuator of the multi-chamber of deflection indicates software using a kind of method that combination deflects direction vector and deflection angle The deformation of actuator；The characteristics of according to pneumatic software actuator pressure control and flexible deformation, by assembly posture correction Control process is divided into assembly posture perception and assembly two stages of pose adjustment:

In the assembly posture perception stage, pneumatic soft robot is considered as a Bending Deformation sensor, according to the gas of each chamber Pressure is worth the deflection direction vector of available soft body deformation, according to the atmospheric pressure value of each chamber feedback and The Ideal-Gas Equation The volume change of soft body deformation process is calculated, and then current volume variation is calculated according to the continual curvature criterion of elastic material deformation Under bending angle；

In the assembly pose adjustment stage, multi-chamber software is considered as air bending actuator, according to the Yeoh of elastomer this structure mould Type and the relationship of the principle of virtual work available air pressure acting and bending angle, the air pressure by controlling each chamber make software to finger Fixed direction is bent with specified angle, to realize assembly posture correction.

2. the software actuator control method of robotic asssembly posture correction as described in claim 1, which is characterized in that for One software actuator with n chamber, software actuator control method the following steps are included:

Step 1: the bending direction vector of each chamber of software actuator is determined

Select the bottom section of software actuator as projection reference surface, selection software actuator bottom centre point is origin, Plane coordinate system is established on projection reference surface, is kept each chamber control pressure of pneumatic software actuator equal, is then increased software The control pressure of i-th (1~n) chamber of actuator makes software actuator generate bending, by pneumatic actuator axis in projection base Unit vector on quasi- face projecting directionBending direction vector as the i-th chamber；

Step 2: each chamber pressure situation of change of acquisition standard assembling process

During robot completes standard assembly, at interval of the gas of same time acquisition each chamber of nk group software actuator Press data P_i,j, wherein i=1~n represents the variant chamber of software actuator, and j=1~k is represented to be acquired when executing assembly movement Each chamber pressure value serial number arrived；

Step 3: assembling deviation situation is judged

When robot executes fittage, when being spaced time acquisition the i-th chamber of software actuator difference identical with step 1 The air pressure value of feedback P ' at quarter_i,j, compare P_i,jWith P '_i,jDifference, if

|P_i,j-P’_i,j|>δ (1)

Then think that error occurs in assembling process, records current each chamber pressure value P '_iAnd robot is notified to stop assembly movement and retract To home, wherein δ is set allowable error range；

Step 4: there is software posture perception when rigging error

When assembling process generates error, software actuator generates bending under external force, and bending direction is outer masterpiece The external force on software actuator is acted on each chamber pressure to software brake according to the interaction of power at this time with direction Resultant force it is reversed；According to the atmospheric pressure value of each chamber in the case of each chamber flex direction vector and bending determined in step 1 P’_i, each chamber pressure is to the bending direction vector of software actuator resultant force under available error condition

Wherein n is actuator pneumatic cavity number of chambers mesh,For the bending direction vector of the i-th chamber,

Then bending direction of the software actuator under error condition and this direction vector are on the contrary, i.e.

Software actuator Bending Deformation process work in the case of rigging error is assumed with Simplified analysis, according to perfect gas shape State equation, the relationship between gas volume V and air pressure P are

Wherein n is gaseous matter amount, and R is gas constant, and T is temperature, then according to the cavity body before software actuator Bending Deformation It accumulates, air pressure, the atmospheric pressure value and formula (4) after Bending Deformation obtain the software actuator air cavity volume V after deformation occurs_m；

Further, the bending angle θ and software actuator volume V being bent according to the cross sectional shape of software actuator after deformation_m Relationship

θ=f (V_m) (5)

The bending angle that the software actuator bending direction and formula (5) then provided according to formula (3) provides determines rigging error When software actuator assemble posture；

Step 5: software actuator assembles pose adjustment

According to the assembly posture sense in the contact force of component assembly process, fits kind analysis and step (4) when assembling deviation Know, obtain the correct assembly posture under error current situation, i.e., the deflection direction of software actuator when correctly being assembled to AmountAnd deflection angle θ_c；

By each chamber pressure expressed in formula (2) to the bending direction vector of software actuator resultant force, then have

Wherein P_in,iGas pressure intensity is inputted for each air cavity, n is actuator pneumatic cavity number of chambers mesh,For the i-th chamber bending direction to Amount；

Based in step 4 hypothesis and formula (5) obtain software actuator bending angle be θ_cWhen each air cavity volume V_m,i

V_m,i=g_i(θ_c) (i=1~n) (7)

Wherein n is software actuator air cavity number, g_i() is bending angle θ_cWith each air cavity volume V_m,iBetween functional relation；

During software actuator assembles pose adjustment, compressed gas work done be entirely used for overcoming external constraint power and Rubber material internal stress work done establishes balance expression according to the principle of virtual work

Wherein dV_c,iFor air cavity volume change before and after pose adjustment, V_{R, i}For each air cavity rubber material volume, W_ouTo overcome outside Work done is constrained, W is rubber material energy density function, using second order Yeoh constitutive model strain energy density function, then

Wherein, C₁₀, C₂₀For material parameter, λ is actuator shaft to principal elongation ratio；

It is defeated to substitute into each air cavity needed for each section known quantity acquires the correction control of software actuator posture for simultaneous formula (6)~(9) Enter gas pressure intensity P_in,i, reaching desirable value by control input gas pressure intensity can be adjusted pneumatic software actuator to correct assembly Posture, and return step three re-executes assembly movement.

3. the software actuator control method of robotic asssembly posture correction as claimed in claim 2, which is characterized in that described In 4th step, for the software actuator Bending Deformation process in the case of rigging error, make the following assumptions with Simplified analysis:

4.1) pneumatic software actuator is without being radially expanded, i.e. section exterior contour size constancy；

4.2) the rubber material even variation of pneumatic software actuator air cavity outer wall；

4.3) do not consider to strain the mechanics influence that limiting layer generates overall deformation process；

4.4) overall volume of elastic matrix remains unchanged before and after deformation；

4.5) the pneumatic software actuator of multi-chamber is in bending deformation process mean curvature even variation.