KR20010090901A - 6 Degree of Freedom Parallel Haptic Device - Google Patents

Abstract

PURPOSE: A 6-degree of freedom parallel haptic instrument is provided to offer a practical interface by using plural degree of freedom more than those of the currently used haptic instrument and to offer a parallel haptic instrument no having a load caused by a self-weight by a light and wide working space and the optimum designing method for the instrument. CONSTITUTION: Three bridges are located having 120-degree intervals and comprised by five links(L1¯L5), respectively, are provided. Three upper contacting points(4) exist on the upper plate away from the radius Rt based on the upper plate coordinate system and comprises globe-shaped joints being connected to a link L2 with the upper plate. Three lower contacting points(3) exist between two links(L4, L5) and comprises globe-shaped joints. Three lower operating devices(1) are located having 120-degree intervals in the vertical direction based on the reference coordinate system and are connected with a link L3. Three upper operating devices(2) are located having 120-degree intervals in the horizontal direction from the reference coordinate system in the above direction of the lower operating devices(1) and are connected with a link L1.

Description

6 Degree of Freedom Parallel Haptic Device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a haptic instrument that provides a user with a sense of reality through hands or tactile senses, and more particularly, to a method for determining kinematic optimum design and driving capacity of a haptic instrument. Virtual reality technology has been used for remote control, simulation, etc., and the scope of application is gradually expanded due to the recent development of information and communication technology and changes in market demand. If a user uses a virtual reality system, the interface to such a system becomes a problem. An interface refers to an area or boundary that both sides share when a human touches a tool. A representative interface with a computer has been a mouse or a keyboard. Recently, as the research on virtual reality is active, the necessity for a haptic interface that provides a sense of reality through the five senses, including the sense of touch, is increasing.

Previously known researches on haptic interfaces include PHANToM, developed at MIT University and limited use for surgery, MagLev Wrist developed at Carnegie Mellon University, and pen-type haptic devices developed at University of Washington. Previous studies such as the above had many studies on mechanisms having a degree of freedom of less than three degrees of freedom in which the direction of movement is limited to three. However, in the conventional three degree of freedom mechanism, each leg is formed by one chain and is moved by two drivers. In order to drive each leg, one driver is fixed to the ground and the other driver is connected to a moving link rather than the ground. Since it is driven, the weight of the driver is included in the weight of the system itself, which increases the weight of the entire system. Therefore, when the conventional parallel mechanism is to be used for haptic, the burden of the weight of the system that the user must drive due to the weight of the driver itself increases, so that fatigue is increased when using it for a long time. There was a disadvantage of deterioration. Conventional parallel mechanisms with more than three degrees of freedom exist, but this mechanism has a disadvantage that the working space is not uniform as a result of the unique shape due to the structure in which the lower driver is located in the same direction as the upper driver.

In the present invention, a practical interface can be provided using more degrees of freedom than conventional haptic instruments, and a parallel haptic mechanism having a light and large work space and no burden due to its own weight, and an optimal design method and driving thereof We propose a method for dose determination.

1 is an overall perspective view of a six degrees of freedom parallel haptic mechanism proposed in the present invention;

Figure 2 is an enlarged view of the main part of the six degrees of freedom parallel haptic mechanism proposed in the present invention,

Figure 3 is a cross-sectional view of the six degrees of freedom parallel haptic mechanism proposed in the present invention.

* Description of the main parts of the drawings *

1: lower driver 2: upper driver

3: lower contact point (spherical joint) 4: upper contact point (spherical joint)

5: cylindrical joint 6: top plate

7: parent chain 8: child chain

L1-L5: Link

In order to achieve the object as described above, the parallel haptic mechanism proposed by the present invention is present at intervals of 120 degrees, three legs each consisting of five links (L1 ~ L5); Three upper contact points 4 of spherical joints on the upper plate which are at a distance of radius Rt around the upper plate coordinate system and which connect the upper plate and the link L2; Three lower contact points 3 between the two links L ₄ , L ₅ and of spherical joints; Three sub-drivers (1) present on the ground at 120-degree intervals in a vertical direction about the reference coordinate system and connected to the link L3; It characterized in that it comprises three upper drivers (2) which are present at intervals of 120 degrees in the horizontal direction from the reference coordinate system over the lower driver and connected to L1.

Hereinafter, with reference to the accompanying drawings, it will be described in detail the structure and kinematic analysis of the six degrees of freedom parallel haptic mechanism according to the present invention.

1 is a view of the overall perspective view of a parallel haptic device proposed in the present invention, Figure 2 is an enlarged view of the main part of the haptic device, Figure 3 is a cross-sectional view of the haptic device.

As shown in Fig. 1, the six degrees of freedom parallel haptic mechanism is composed of a top plate 6, a ground driver (1, 2) and three legs connecting them. The upper plate has three upper contact points in the form of a spherical joint at 120 degree intervals from the upper plate coordinate system. Three pairs of actuators are located on the ground in three directions of 120 degrees with respect to the center reference coordinate system. The reason why all the drivers are attached to the ground is to eliminate the burden of their own weight. The distance from the origin of the reference coordinate system to the upper driver 2 located in the horizontal direction is defined as RB1, the horizontal distance from the lower driver 1 located in the vertical direction is defined as RB2 and the vertical distance to the lower driver 1 is defined as HB. . As can be seen in Figure 2, the three legs connect the upper contact point and the upper driver 2, respectively, the upper chain 7 consisting of a path connecting the link 1 and link 2, and the lower contact point ( ^m ) of the spherical joint type D , m = 1, 2, 3) and the lower driver (1) and consists of a lower chain (8) consisting of a path along Link3->Link4->Link5-> Link1. Unlike the conventional parallel haptic mechanism, all the actuators are attached to the ground, so the mechanism that connects the lower chain to each leg is selected. Three upper and three lower actuators give the system driving force, with the exception of the joints. Among the passive joints, the cylindrical joint rotates in one direction, and the spherical joint can rotate in three directions. The two chains are driven by being constrained to the lower contact point, and the rotational movement of the upper actuator attached to the upper chain contributes to the vertical movement of the upper contact point of the chain, and the rotational movement of the lower actuator attached to the lower chain is upper The position and movement of the top plate are determined by the cooperation of the three legs by contributing to the left and right movement of the contact point.

Hereinafter, a method of analyzing the haptic mechanism kinematically to find the Jacobian of the haptic mechanism and to analyze various performance indices of the device based on the same.

To get Jacobian, the speed of the joint ) And top plate output speed ( ) Should be identified. In order to find this, the position vector of the top plate and the position vector of the upper contact point must be obtained first. The position vector of the upper plate coordinate system with respect to the lower reference frame is defined by the following equation.

[Equation 1]

The first term means the position of the top plate and the latter term means the azimuth of the top plate.

The position vector of the upper contact When defined as The position vector of the first upper contact point is It is expressed as Equation (2).

[Equation 2]

Equation 2 is the position vector of the top plate and the position vector from the center of the top plate to the upper contact point Can be rewritten as in Equation 3 below.

[Equation 3]

here Is, Represents the rotation matrix of the upper plate coordinate system with respect to the reference coordinate system, For the tops coordinate system Position vector of the first upper contact point.

In order to determine the relationship between the upper contact point and the speed of the upper plate, the derivative of Equation 3 is as follows.

[Equation 4]

here to be.

Equation 4 may be written as Equation 5 in a matrix form.

[Equation 5]

here Is the same as Equation 6.

[Equation 6]

Output velocity vector from equation (5) Velocity vector of the contact point It can be seen that the relationship with the equation (7)

[Equation 7]

here Is defined as in Equation 8.

[Equation 8]

The first kinematics for the upper chain of each leg is defined by the following equation (9).

[Equation 9]

here Is the velocity vector of the joints forming the upper chain of the mth leg.

As described above, each leg has a lower contact point between the upper chain and the lower chain. Since it is constrained to form a closed chain, at D point, the lower chain and the upper chain have the same speed and position. Therefore, equation (10) can be found from equation (9).

[Equation 10]

When the lower chain has a non-specific shape, Equation 10 is rearranged using an inverse transformation relationship to obtain a linear relationship between the joint vector of the upper chain and the joint vector of the lower chain as shown in Equation 11.

[Equation 11]

Drive joint of each leg from equation (11) And joints that make up the parent chain ( Velocity relation between the two is given by Equation (12).

[Equation 12]

here Is defined as in Equation 13.

[Equation 13]

Substituting the inverse of Equation 9 into Equation 12, the velocity relationship between the driving joint and the upper contact point may be defined as shown in Equation 14.

[Equation 14]

Substituting this back into Equation 7 gives Equation 15 representing the speed relationship between the drive joint and the output vector.

[Equation 15]

When the system is a non-specific shape, Equation 15 is expressed as Equation 16 through inverse change, which is a Jacobian of the haptic system.

[Equation 16]

The Jacobian of the haptic system obtained by Equation 16 is the basis for calculating the kinematic performance index. Hereinafter, a work space, a maximum force transmission ratio, and an isotropic index, which are considered in the design of the haptic mechanism proposed by the present invention, will be described.

The working space refers to the space where the end device is reachable and can have any azimuth in all directions at that point, which is defined by Equation 17 and the range of the azimuth is Equation 18.

[Equation 17]

Equation 18

The isotropic index is about how uniform the velocity distribution can be in all directions in the work space of the end device of the haptic instrument. The larger the value is, the more uniform the velocity distribution becomes. It is defined as the ratio of.

[Equation 19]

However, Jacobian has both terms for linear and rotational speeds, so they must be converted to the same dimension in order to be integrated. To this end, in the present invention, the proportional Jacobian [Dimensional Jacobian] using the nominal length means the distance from the reference coordinate system to the center of the main work space [ ]. Proportional Jacobian is defined as in Equation 20.

[Equation 20]

Therefore, the proportional isotropy index is defined as Equation 21, and the global proportional isotropy index is defined as in Equation 22.

[Equation 21]

[Equation 22]

The maximum force transmission ratio means the maximum joint input torque for exerting the unit output force at the end of the haptic mechanism and is defined as in Equation 23 below.

[Equation 23]

The global maximum force transmission ratio distributed over the entire workspace is defined as in Equation (24).

[Equation 24]

In order to support a constant force, the smaller the driving force is, the more efficient it is.

In order to optimize the design of the haptic mechanism under given conditions, the various performance indices described above should be taken into consideration. In the present invention, by introducing the concept of a composite global design index to propose a method that can obtain the solution of the optimal design when designing haptic mechanisms. In order to consider each performance index comprehensively, it is necessary to dimensionize different performance indices of different units. In the present invention, a fuzzy theory of changing the indices of various dimensions to a value between 0 and 1 is used as a dimensionless method. . According to this, the anisotropy index and the global maximum force transmission ratio such as the work space and the global proportion are redefined as Equations 25, 26 and 27, respectively.

[Equation 25]

[Equation 26]

[Equation 27]

The complex global design index considering the above design index is calculated as shown in Equation 28 below.

[Equation 28]

The design factor when the value of the composite global design index is the maximum is the solution of the optimal design. At this time, the design factors include the radius Rt of the top plate, the length of the links constituting each leg l ₁ , l ₂ , l ₃ , l ₄ , l ₅ , the horizontal distance RB2 to the second driver 1, the vertical distance HB, and the like. have. When the user designs the haptic device, the user can perform the optimal design using Equation 28 while modifying the design factor in consideration of a given operating environment.

The present invention proposes a method for determining the optimum capacity of a drive system using the characteristics of the designed mechanism. The maximum load imposed on each drive is determined as the optimum capacity of that drive by the amount of force applied to the end device. Maximum load capacity required , The maximum driving force on each drive under the following constraints: Obtain The constraint is set as in Equation 29.

[Equation 29]

here, Is the displacement of the i joint Is the total number of joints. At this time, the load on the end device can be expressed as shown in Equation 30.

Equation 30

load on the nth drive And gravity-induced load Since the optimum driving capacity is determined by Equation 31,

Equation 31

As described above, according to the six degrees of freedom parallel haptic mechanism proposed in the present invention, a more practical interface can be provided by utilizing many degrees of freedom, and all the drivers are attached to the ground, so there is no burden due to the weight of the drivers themselves. The weight of the instrument is light and the working space is increased. In addition, the user can design the optimal system considering the working environment through the system optimization design method considering the various performance indices, and maximize the work efficiency by selecting the actuator reflecting these system characteristics.

Claims (3)

Claims [1] A parallel haptic device comprising: three legs which are disposed at 120 degree intervals and consist of five links L1 to L5; Three upper contact points 4 of spherical joints on the upper plate which are at a distance of radius Rt around the upper plate coordinate system and which connect the upper plate and the link L2; Three lower contact points 3 between the two links L ₄ , L ₅ and of spherical joints; Three sub-drivers (1) present on the ground at 120-degree intervals in a vertical direction about the reference coordinate system and connected to the link L3; And six upper actuators (2) which are spaced 120 degrees horizontally from the reference coordinate system above the lower driver and connected to L1. 6. A six degree of freedom parallel haptic device according to claim 1, characterized in that the six upper and lower drivers (1,2) are attached to the ground to eliminate the burden of their own weight. The method of claim 1, wherein when designing the six degrees of freedom parallel haptic device, design factors are determined using a global hybrid optimal design method that simultaneously considers the workspace, isotropy, and maximum force transmission ratio of the device. 6 degrees of freedom parallel haptic mechanism.