PRESENCE 2007

Constraints for Realistic Hand Manipulation
Salvador Cobos, Manuel Ferre, Miguel Angel Sánchez-Urán and Javier Ortego
Universidad Politécnica de Madrid{cobosalvador, mferre, jortego@etsii.upm.es}, {miguelangel.sanchezuran@upm.es}
Abstract
This paper describes dynamic constraints of a human
hand model. Inter-finger and intra-finger constraints havebeen develop in order to obtain quite realistic manipulation.
Keywords--- human hand model, inter-finger, intrafinger, constraints.

1. Introduction
The objective of this work consists of achieving realistic
hand manipulation performed by their kinematicconfiguration and by inter-finger/intra-finger constrains that
imitate the human motion in order to obtain a realistic handmanipulation and representation of the hand model.
Cyberglove [1] was used for checking previous constraints
and testing new constraints for more acceptableapproximations so that more realism in grasp movement.
Several tests with the Cyberglove have been performed toverify the human hand model. Kinematic model of the human
hand is modeled in two representative models [2, 3]. The firstmodel represents the kinematic model of the fingers: index,middle, ring and little with five degrees of freedom each one.
The second model represents the kinematic model of thethumb with four degrees of freedom. All constraints aredeveloping for these two models. The organization of thiswork is in two parts: the Section 2 relates constraints for twomodels and finally, conclusions are presented.

2. Constraints
Fingers carry out movements in specific range caused bystatic constraints, intra-finger constraints and inter-fingerconstraints. These two mentioned constraints are often called
dynamic constraints, which are responsible of giving natural
movements statically and dynamically. However, this rangeof movement is somewhat ambiguous because the range
depends on various factors involving human handbiomechanics. The ranks of movement of each joint arerepresented by static constraints [4, 5, 6].
The hand has two types of movements: active and passive.
Active movements are actuated by muscles and tendons that
permit a range of free movement, and passive movements arerange of movements not actuated. The hyperextension inInterphalangeal (IP), Distal interphalangeal (DIP) andTrapeziometacarpal (TMC) joints are considering such as
passive movement.
In this paper, new constraints have been implemented ininter-finger and intra-finger so as to acquire realistic
movement of the hand model. This realistic movement
generates an adequate degree of presence when the userinteracts with the application.
Intra-finger constraints have been developed to reproduce
movements within of the rank of grip trajectories such as
circular and prismatic grasps.
Inter-finger constraints have been verified in experiments
carried out with a Cyberglove to obtain the dependency oftendons mainly among the middle, ring and little fingers. The
functionality of this glove depends on calibration of the joints[7].

a)b)d)c)e)

Figure 1 Represents intra finger constrains a) Middle andring. b) Middle, ring and little. c) Abduction / adduction
between ring and little. d) Little and ring e) Index andmiddle.
2.1 Intra-finger Constraints
Intra finger constraints refer to dependency of joints
internals. In this section, intra-finger constraints are divided
into two categories, the first is for index, middle, ring andlittle fingers, and the second for thumb model.
2.1.1 General finger model
Intra- finger constraint θDIP ≈ 2/3 θPIP has been accepted byseveral researches as [8] and efficiently checked in ourexperiments. However, the constraint for θPIP ≈ 2θMCP (f/e) [9]in experiments carried out had been inappropriate. It is369/388

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because θPIP and θDIP depends on variation of θMCP (f/e). The
trajectory of the finger with this constraint becomes veryclose. Consequently, is proposing a new constraint for θPIPand θMCP (f/e) as equation (1).

3
θ pip ≈ θ MCP ( f / e )47
θ MCP ( f / e ) Litle
122
θ MCP ( f / e ) Ring ≈ θ MCP ( f / e ) Middle
3
θ MCP ( f / e) Ring − θ MCP ( f / e) Middle < 60º(8)θ MCP ( f / e ) Ring − θ MCP ( f / e ) Litle < 50 º(10)θ MCP ( f / e ) Ring ≈(1)

(7)

(9)

2.1.2 Thumb model
The type of constraints being presented has been developedfor θIP, θMCP (f/e) and θTMC (f/e). The following equations (2) and(3) show the intra constraints for thumb model.

12θ IP ≈ θ MCP ( f / e )54

θ MCP ( f / e ) ≈ θ TMC ( f / e )The Second relationship is when MCP flexion exists in theindex finger as shown in figure 1.e. Equation (11) represents
this type of relationship between the index and the middlefingers.

15(2)
(3)

2.2 Inter-finger Constraints
The inter-finger constraints were obtained by using the handmodel and Ciberglove. These types of constraints are coupled
movements among index, middle, ring and little finger. The
relationship among angles with middle, ring and little finger
has been measured to represent real movements of the handmodel.
2.2.1. Cases of coupling movements. There exist
coupling movement when there is flexion in θMCP (f/e) and theflexions of index and little finger are equal to zero. When thisunique flexion is generated, the flexion of middle finger isequal to the flexion of ring finger as described in equation(4). Such as shown in figure 1.a(4)θ MCP ( f / e ) M ≈ θ MCP ( f / e ) R
Another coupling movement is produced when there isflexion solely in the ring finger θMCP (f/e). This causes theflexion of middle finger to be equal to the flexion of littlefinger as described in equation (5). Such as shown in figure
1.b(5)
θ MCP ( f / e ) M ≈ θ MCP ( f / e ) L
Finally, coupling movement in abduction / adduction isgenerated among ring and little fingers. In most cases, themovement is similar to equation (6). Such as shown in figure
1.c(6)
θ MCP ( abd / add ) R ≈ θ MCP ( abd / add ) L
2.2.2 Relations of angles. This kind of relationship issummarized in two types; the most important relationship iswhen flexion in MCP of little finger exists as shown in figure
1.d. Equations (7), (8), (9) and (10) represent this type ofrelationship among these fingers.

θ MCP ( f / e ) Middle ≈ θ MCP ( f / e ) Index(11)

Conclusions
New constraints for inter-finger and intra-finger werepresented and it allows a reasonable representation ofindependence among joints and fingers. These constraints arevery important because they are responsible for generating
realistic movements of the hand model simulating a realhuman hand.

Acknowledgements
This work is supported by the European commission underthe IMMERSENCE integrated project of the sixth frame
program (IST-4-027141-IP).

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