RU2009834C1 - Method for automatic control of machining of spherical surfaces - Google Patents

Abstract

FIELD: machining. SUBSTANCE: when machining the tool clamping force is controlled depending on variation of the area of contact of the tool and the part, and the time in which the tool passes particular sections of the trajectory. The trajectory is defined by the movement of the point of intersection of the tool axis of symmetry and the surface of the machinable part. EFFECT: improved accuracy. 8 dwg

Description

 The invention relates to the processing of spherical surfaces and may find application in the optical industry for processing lenses, as well as for processing spherical surfaces, in particular spherical kinematic pairs of manipulators and large-diameter balls.

 A known method of automatic control of the processing of spherical surfaces, which consists in measuring the frequency of rotation of the tool during the entire processing cycle, comparing it with the calculated one and by the signal of the mismatch between them changing the clamping force, while in case of exceeding the rotational speed of its calculated value, the clamping force is increased [ 1] .

The disadvantage of this method is that it does not pre-calculate the value of the nominal force Q ^{n of the} clamp tool in function of its movement on the surface of the part.

 The purpose of the invention is to improve the quality of processing.

This is achieved in that they determine the law of change in the clamping force Q ⁿ from the condition that Q ⁿ = A ⁿ ˙ S ⁿ ˙ V _s ⁿ , where S ⁿ is the nominal (calculated) contact area of the contacting surfaces of the tool and the workpiece, V _with ⁿ - nominal (calculated) speed of moving the point C of the intersection of the axis of symmetry of the tool and the surface of the workpiece, A ⁿ = P ⁿ ˙ t _pr ⁿ is a constant parameter that determines the required quality and productivity of the processing process, P ⁿ = Q ⁿ / S ⁿ is the pressure in the zone contact of the tool and the workpiece; t _CR ⁿ - the function of changing the time from the distance traveled L points C, satisfying the given quality of processing.

и по сигналу рассогласования с параметром А^н изменяют силу прижима, увеличивая ее при А^д < А^н и уменьшая при А^д > А^н.Then measure the actual value of speed V _from ^d point C, the value of the actual force Q ^d clamp during the movement of point C along a given path, as well as the actual area S ^{d of} contact of the tool with the workpiece, form electrical signals proportional to the parameters Q ^d , S ^d and V _with ^d , determine the electrical signal proportional to the parameter A ^g =

and the signal mismatch with the parameter And ⁿ change the force of the clip, increasing it at A ^d <A ⁿ and decreasing at A ^d> A ⁿ .

A significant difference of the proposed method is that when it is implemented, the value of the parameter A ⁿ , which determines the required quality and productivity of the processing process, is automatically kept constant. This factor contributes to the removal of a uniform layer of material from the part and, therefore, to improve the quality of its processing.

In FIG. 1 shows a diagram of the relative positioning of the tool and the workpiece; in FIG. 2 is a view along arrow A in FIG. 1 with an additional partition of the surface of the tool and the part into spherical belts; in FIG. 3 - speed V _ci ^{n of the} point C of the tool on each i-th section of the path L, which is a whole function V _c ⁿ = f (L); in FIG. 4 - _dwell time t _pr ^{n of the} point C of the tool in each i-th section, which is a function t _pr ⁿ = f (L) and the dash-dot line is the current time t; in FIG. 5 - contact area S _i ^{n of the} tool and the workpiece on each i-th section of the path, which is a function of S ⁿ = f (L); in FIG. 6 - pressure P _i ⁿ at each i-th section, which is a function of P ^A = f (L); in FIG. 7 - clamping force Q _i ^{n of the} tool to the workpiece at each i-th section, which is a function of Q ⁿ = f (L); in FIG. 8 is a block diagram of a system for automatically controlling the processing of spherical surfaces on ШП type machines.

 The scheme for implementing the method includes a part 1 and a tool 2.

The method consists in initially assigning the trajectory of the portable movement of tool 2 along part 1. Let this trajectory be a closed curve in the form of a circle centered at point C _o , formed by the intersection of a straight line passing through the center of curvature of part 1 at an angle Δ K _o relative to it axis of symmetry with the machined surface.

и углами Ψ и Δ К в неподвижной системе координат ХYZ, связанной с центром обрабатываемой сферической поверхности.Then, on the adopted trajectory, point C is selected, which is the intersection of the axis of symmetry of tool 2 with the workpiece surface 1. The location of this point can be determined by a radius vector

and angles Ψ and Δ K in a fixed coordinate system XYZ associated with the center of the processed spherical surface.

In FIG. 2, the surface of the tool and the part was further divided into spherical belts by circles, which makes it possible to determine the number of points of intersection and contact of the upper and lower links and determine, with the required accuracy, the area S ^{n of the} contact of the tool with the workpiece, and with an increase in the number of circles spherical belts increases accordingly the accuracy of determining the area S ^{n the} contact of the tool and the part.

 Suppose that, moving along a selected path, the tool (point C) sequentially passes through points A, B, C, D, i.e., it moves counterclockwise relative to the fixed coordinate system XYZ. Moreover, points A, B, C, D divide the trajectory L into four equal sections.

Consider the algorithm for compiling a "hard" control program for the strength of Q ⁿ for machine tools such as silos.

From the condition that the value of the parameter A ⁿ , which determines the required quality and productivity of processing, be kept constant, it is possible to pre-calculate the law of change in the clamping force Q ⁿ , knowing the law of change in the contact area S ^{n of the} tool and the workpiece, for a given trajectory of point C and speed V _s ⁿ , as a function of the distance L traveled by C.

есть некоторая функция от пройденного пути точкой С, воспроизведение этой функции обеспечивает "жесткое" программное управление силой прижима. Так, например, для станков типа ШП максимальный путь, пройденный точкой С определяется размахом выходного звена исполнительного механизма, при обработке плоскостей траектория точки С - дуга окружности. Скорость точки V_c = f(L) как некоторая функция от пути легко определяется скоростью выходного звена исполнительного механизма. Таким образом, зная требуемую производительность q =

, где Т - время кинематического цикла, за которое точка С возвращается в исходное положение; n - количество кинематических циклов, необходимое для съема припуска обрабатываемой поверхности, определяют время кинематического цикла T =

(время одного оборота кривошипа исполнительного механизма). Скорость же точки С, например, для станков типа ШП в каждом i-том шаге легко найти, представив функцию в дискретном виде. Так время пребывания точки С в каждом участке пути i, i-1 определяется по формуле: t $\genfrac{}{}{0ex}{}{\text{н}}{\text{п}}$ _рi=

. Причем, как видно из фиг. 4, T= 2

t $\genfrac{}{}{0ex}{}{\text{н}}{\text{п}}$ _рi.In this case, the obtained value Q ⁿ = A ⁿ · S ⁿ ·

there is some function of the path traveled by point C, the reproduction of this function provides a “hard” software control of the clamping force. So, for example, for SHP type machines, the maximum path traveled by point C is determined by the amplitude of the output link of the actuator; when processing planes, the path of point C is an arc of a circle. The speed of the point V _c = f (L) as a function of the path is easily determined by the speed of the output link of the actuator. Thus, knowing the required performance q =

where T is the time of the kinematic cycle, during which point C returns to its original position; n is the number of kinematic cycles required to remove the stock of the machined surface, determine the time of the kinematic cycle T =

(time of one turn of the crank of the actuator). The speed of point C, for example, for ШП type machines in each i-th step is easy to find by presenting the function in a discrete form. So the residence time of point C in each section of the path i, i-1 is determined by the formula: t $\genfrac{}{}{0ex}{}{\text{n}}{\text{P}}$ _pi =

. Moreover, as can be seen from FIG. 4, T = 2

t $\genfrac{}{}{0ex}{}{\text{n}}{\text{P}}$ _pi .

The required quality of the processed surface in the proposed technical solution is linked to the pressure value P ⁿ = Q ⁿ / S ⁿ . So, for given diameters of the workpiece d _n and tool d _in , as well as the radius R of the machined sphere, the dependence S ⁿ = f (L) is analytically established. Such a function S ⁿ = f (L) is determined for each trajectory of point C. Next, the path L is divided into N equal sections, as shown in FIG. 3 N = 10.

·t $\genfrac{}{}{0ex}{}{\text{н}}{\text{п}}$ _рi= P $\genfrac{}{}{0ex}{}{\text{н}}{\text{i}}$ ·t $\genfrac{}{}{0ex}{}{\text{н}}{\text{п}}$ _рi, где Р_i ^н = Q_i ^н/S_i ^н - давление в зоне контакта инструмента и обрабатываемой детали на участке i, i-1.In each section i, i-1, the average value of the contact area S _i ^{n of the} tool and the workpiece is determined as a function of the path L of the point C. The clamping force Q _i ^{n of the} tool and the workpiece in each section i, i-1 is determined from the condition that it remains constant parameter A _нi =

T $\genfrac{}{}{0ex}{}{\text{n}}{\text{P}}$ _pi = P $\genfrac{}{}{0ex}{}{\text{n}}{\text{i}}$ T $\genfrac{}{}{0ex}{}{\text{n}}{\text{P}}$ _pi , where P _i ⁿ = Q _i ⁿ / S _i ⁿ is the pressure in the contact zone of the tool and the workpiece in section i, i-1.

), сила же прижима Q_i ^н меняется в соответствие с изменением площади контакта инструмента и обрабатываемой детали, а также с изменением времени t_прi ^н пребывания инструмента на каждом участке i, i-1 траектории L точки С.Thus, the proposed control method involves maintaining the constancy of the value of the parameter A _i ⁿ (i =

), the force of the clamp Q _i ⁿ changes in accordance with the change in the contact area of the tool and the workpiece, as well as with the change in the time t _pr ⁿ of the tool stay in each section i, i-1 of the trajectory L of point C.

Such an algorithm for developing the calculated clamping force can be used for most types of machines operating in the opto-mechanical industry. It can be used to compile programs that provide "hard" control by the force of Q ⁿ . Unaccounted (random) factors leading to a deviation from the described "hard" program control by the force Q ⁿ can be taken into account by introducing feedback on the parameter A _i ⁿ , which keeps a constant value for the entire time T of the kinematic cycle. In this case, in case of deviation of the actual value from the nominal value, A _i ⁿ change the pressing force, increasing it if A _ni > A _di and decreasing if A _ni <A _di .

 The block diagram of the automatic control system for the processing of spherical surfaces on ШП machines consists of a control unit (control system), a group of amplifiers U1, U2, U3, U4, U5, actuators IM1, IM2, multiplication units for nominal values of BPN and actual values of BPD , BS comparison unit, TG tachogenerator, TD strain gauge, scanning device, workpiece 1 and tool 2.

The automatic control system operates as follows. The SU unit generates electrical signals proportional to the nominal speed V _from ^{n the} point C of the tool supplied to the amplifier U1 and BPN, the nominal force Q ^{n of the} clamp of the tool to the workpiece supplied to the amplifier U2 and BPN, the nominal area S ^{n of the} contact of the tool and the workpiece, arriving at the BPN. Electrical signals from amplifiers U1 and U2 are fed to actuators IM1 and IM2, providing respectively a change in speed V _c ^{d of} point C and clamping force Q ^d according to the nominal law. Electrical signals of the TG tacho generator, proportional to the actual speed V _s ^{d of the} tool, from the TD strain gauge, proportional to the real force Q ^{d of the} tool pressing against the workpiece, from the scanning device, proportional to the actual area S ^{d of the} tool and part contact, are fed to the BJP.

From the multiplication units of the nominal BPN and actual BPD parameters, electrical signals proportional to the parameters A ⁿ and A ^d , respectively ^, through the sensors U3 and U4 are fed to the BS comparison unit. The latter makes a comparison of the parameters A ⁿ and A ^d, and if the actual value of the parameter A ^d deviates from the nominal A ^{n, it} generates an electric signal supplied to IM2 and changes the force Q ^{n of the} clamp, increasing it if A ⁿ > A ^d and decreasing if A ⁿ <A ^d . (56) 1. USSR author's certificate N 1496991, cl. B 24 V 13/00, 1989.

Claims (1)

 METHOD FOR AUTOMATIC CONTROL OF SPHERICAL SURFACES PROCESSING, in which they change the strength of the tool to the surface of the part depending on the change in the parameters that characterize the processing process, which differs in that the quality is changed in order to increase the quality and the time the tool passes the specified sections of the toolpath, which is determined by the movement of the point of intersection of the axis of symmetry of the tool to the surface of the workpiece .

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