3. Analysis and results
Kinematics is the first step in the study of the robot manipulator mechanism, considering
only space-time relations and negligible forces and their effects. The study of the
dynamic properties of the robot manipulator, as well as the organization of its control,
requires the creation of a dynamic model of the robot of universal appearance, which
is common to mechanisms with different kinematic structures. Including, we will consider
the example of "Effort collaboration robot 5" (ECR5), PUMA and SCARA research object,
built on the basis of the Lagrange-Euler equation in studying the dynamics of multi-link
manipulators (MLM) [4,5,6]. Because in these robots, only mobile movement levels are considered. In addition,
control parameters corresponding to the dynamic characteristics of movement levels
in the specified coordinate systems are close to each other. The Lagrange-Euler equation
is used to calculate the criterion for evaluating the dynamic characteristics of multi-link
manipulators and the factors affecting their high accuracy in service, and its general
form is as follows:
where 𝑛− is the number of movement levels of MLM; 𝑖− mobility level number (𝑖=1,𝑛);
𝑇− total kinetic energy of the executive body and KLM; П−the total potential energy
of the manipulator with the executive body; 𝑞𝑖− corresponding generalized coordinates
of MLM; 𝑞̇𝑖 –derivatives of MLM generalized coordinates; The moments of the generalized
forces created in the 𝑖− th position for the implementation of the given movement
of the 𝑃𝑖− link are described.
With the help of this proposed [7,8,9] mathematical expression, it is convenient to express the effect of full moment in
the 𝑖− th link of 𝑃𝑖 (1) MLM in the following form:
where 𝐻𝑖(𝑞)− is the component describing the inert properties of the corresponding
MLM mobility level; ℎ𝑖(𝑞,𝑞̇)− component of Coriolis forces; 𝑀𝑖(𝑞, 𝑞̇, 𝑞̈)
− is a one-level movement that takes into account the interaction between gravity
forces and all levels and positions of the mobility of the manipulator during movement;
𝑞̈𝑖− describes the generalized acceleration of MLM.
With the help of this mathematical expression, the kinematic schemes of ECR5, PUMA
and SCARA robots of the MLM type, which allow to calculate the degrees of positional
movement, are studied (Figures 1,2,3). The following symbols are given in these pictures:
𝑙𝑖− length, the 𝑖− th link of the MLM, the distance 𝑙𝑖∗− from the center of the
𝑖− th link to the axis of rotation, the 𝑚𝑖 mass of the 𝑖− th link, 𝑚𝑔− describes
the weight of the manipulator's executive body load [10,11,12]. The total potential energy of MLM includes the potential energy of all its links
and loads (Figures 1-2). Calculation of potential energy for robots of type ECR5,
PUMA based on the mentioned kinematic schemes is carried out by the following relationship:
where П2,П3,П𝑔− are the potential energies of the second and third links of MLMs
and the executive load, respectively; 𝑔− acceleration of free fall.
According to the specified coordinate systems, the kinetic energy of each MLM link
is equal to the sum of the forward movements of their centers of mass and the kinetic
energies of rotational movements relative to these centers of mass:
where 𝑣𝑖2− square of the speed of the forward movement of the center of mass of
the 𝑖− th link; 𝐽𝜔𝑖− the moment of inertia of the 𝑖− th link in relation to the
axis passing through the mass center of the link; describes the square of the rotation
speed 𝜔𝑖2− around the axis of rotation of the 𝑖− th link.
Taking into account (4), the following expression can be used to calculate the total kinetic energy of ECR5,
PUMA type MLMs:
where 𝑇П2, 𝑇П3, 𝑇П𝑔− the kinetic energy of the forward movement of the corresponding link centers and
load centers; 𝑇𝑉𝑅1, 𝑇𝑉𝑅2, 𝑇𝑉𝑅3 − describe the kinetic energies of the rotational
movements of the corresponding links relative to their centers of mass.
그림 1. 다중 링크 산업용 로봇 매니퓰레이터 유형 ECR5의운동학 다이어그램.
Fig. 1. Kinematic diagram of multi-link industrial robot manipulator type ECR5.
그림 2. PUMA형 다중링크 산업용 로봇 매니퓰레이터의 운동학적 다이어그램.
Fig. 2. Kinematic diagram of PUMA-type multi-link industrial robot manipulator.
그림 3. SCARA형 다중링크 산업용 로봇 매니퓰레이터의 운동학적 다이어그램.
Fig. 3. Kinematic diagram of SCARA-type multi-link industrial robot manipulator.
In this case, the kinetic energies of rotational movements of the MLM links relative
to the centers of mass 𝑇𝑉𝑅1 have the following form:
𝐽𝑆𝑙 − is the moment of inertia of the first link of the manipulator MLM with respect
to its longitudinal axis, and this link is considered symmetrical with respect to
the axis.
The center of mass 𝑂𝑖 of each link is related to the correct coordinate system,
whose axes 𝑂𝑖 , 𝑥𝑖 , 𝑦𝑖 , 𝑧𝑖 coincide with its main central inertial axes
[13,14].
The calculation of the moment of inertia with respect to an arbitrary axis of rotation
forming angles 𝛼, 𝛽, 𝛾 − with the axes of this coordinate system can be written
as follows [15,16]:
where 𝐽𝑥𝑖 , 𝐽𝑦𝑖 , 𝐽𝑧𝑖 − are the main central moments of inertia of the link;
𝛼𝑖 , 𝛽𝑖 , 𝛾𝑖 − describe the angles formed by the axis of rotation with the main
central axes of inertia.
For ECR5 and PUMA type MLMs with an adaptive position- trajectory control system,
taking into account (7), we can write the moment of inertia of their second link relative to the axis of
rotation passing through the center of mass 𝑂2 in the following form:
Taking into account the mentioned moment of inertia interlink interaction (8), the rotational kinetic energy of the second link of ECR5, PUMA type MLMs is determined
by the following expression:
For ECR5 and PUMA-type KZMs with an adaptive position-trajectory control system, the
moments of inertia of the third link relative to the axes of rotation 𝜔3, its center
of mass passes through𝑂2, taking into account the expression (7), the calculation of the kinetic energy of the third link is as follows:
and taking into account the kinetic energy expression (10), and for ECR5 and PUMA type MLMs, the rotational movement of the third link is as
follows:
The coordinates of the centers of mass of the third links of the ECR5 and PUMA type
MLMs with an adaptive position-trajectory control system are as follows:
and their time derivatives are as follows:
For ECR5 and PUMA-type MLMs with an adaptive position-trajectory control system, taking
into account (12), the second link of the manipulator has the square representation of the linear velocity
of the center of mass,
the kinetic energy of the forward movement of the center of mass of this link is equal
to:
The calculation of the coordinates of the centers of mass of the third links of the
ECR5 and PUMA type MLMs with an adaptive position-trajectory control system looks
like this:
and their time derivatives are as follows:
As a result, taking into account (14), the expression for determining the linear speed of the center of mass of the third
link of ECR5 and PUMA type KZMs with an adaptive position-trajectory control system
is as follows:
for ECR5 and PUMA type KZMs, the expression for determining the kinetic energy of
the forward movement of the center of mass of the third link is as follows:
Determining the load coordinates of ECR5 and PUMA type MLMs with an adaptive position-trajectory
control system can be carried out with the following expressions [2,17]:
and the time derivatives of the load coordinates are determined using the following
expression:
As a result, taking into account (16), the expression of the linear speed of the movement
of ECR5 and PUMA type MLM with load will have the following form:
and the expression of the kinetic energy of its forward movement is written as follows:
Taking into account the above expressions (3), (5), (6), (9), (11), (13), (15) and (17), the Lagrangian function for ECR5 and PUMA typed MLMs will have the following form:
Taking this function and expression (1) into account, the calculation of all parameters of equation (2) for all mobility levels of ECR5, PUMA-type MLMs will have the same form, and their
expressions can be written as follows:
– for a manipulator with one degree of freedom:
– for a manipulator with two degrees of freedom:
– for a manipulator with three degrees of freedom:
The SCARA robot with an adaptive position-trajectory control system is usually a type
of industrial robot working in the Cartesian coordinate system, and since [2,14,17,119] it has two levels of positional mobility, the expressions for calculating the relevant
elements of equation (2) for the kinematic scheme of the KZM (Fig. 3) are as follows only for the first and second links is written:
– for a manipulator with one degree of freedom:
– for the state of two degrees of freedom of the SCARA robot type MLM with an adaptive
positional-trajectory control system:
Taking into account expression (2), it can be said that SCARA robots with adaptive position-trajectory control system
perform movements mainly in coordinates. Therefore, the determination and synthesis
of dynamic properties for one or two degrees of freedom is carried out.
Taking into account expression (2), it can be said that SCARA robots with adaptive position-trajectory control system
perform movements mainly in coordinates. Therefore, the determination and synthesis
of dynamic properties for one or two degrees of freedom is carried out.
Advantage of the chosen calculation method.
The use of this selected Lagrange-Euler equation in the calculation of dynamic characteristics
of multi-link manipulators includes the following advantages:
- the main calculations are related to the kinetic and potential energy of the system;
– the dynamics of the multi-link manipulator is considered as a whole system;
- internal connection reaction forces are excluded from the equations;
- equations are written in symbolic form;
– the resulting expressions are more suitable for modeling and analyzing system properties.
Including the modeling of the dynamics of this multi-link manipulator can be seen
in the example of the following structural scheme (Fig. 4). On the basis of this structural scheme, it is possible to determine and synthesize
the dynamic characteristics of a multi-link manipulator, and to realize the dynamics
[2,17,18,19] of the manipulator as an integrated system on the basis of computer technologies.
그림 4. 다중 링크 매니퓰레이터 동역학 모델링의 구조 다이어그램.
Fig. 4. Structural diagram of multi-link manipulator dynamics modeling.
As a result of the computer modeling of the multi-link manipulator, it is possible
to determine and synthesize the dynamic characteristics of the links according to
the coordinates and the position of the manipulator (Fig. 5).
그림 5. 다중링크 매니퓰레이터의 동적 특성: a) 링크의 좌표에 따라 b- 위치별.
Fig. 5. Dynamic characteristics of multi-link manipulator: a) according to the coordinates
of the links, b- by position.
These obtained dynamic characteristics allow defining and synthesizing the dynamic
model characteristics of the multi-link manipulator in relation to its kinetic and
potential energy as a whole system.