Weizhong Guo

The Design of a New Metal Forming Press with Controllable Mechanism

Metal forming press is one of the most commonly used manufacturing machines. Every day millions of parts are produced by metal forming ranging from battery caps to automotive body panels. Therefore, even a small improvement may add to significant corporative gain. Currently, the metal forming presses can be divided into two categories: mechanical presses and hydraulic presses. The former is fast (high speed presses may reach up to several thousand shots per minute) and energy efficient (the large flywheel eases the impulsive force), but lacks flexibility. On the other hand, the hydraulic presses are flexible (their motions can be programmed) and accurate, but are expensive to build and to operate. Recently, there are mechanical presses driven by seryomotors. They could perform as flexible as hydraulic presses with high speed. Nevertheless, they are even more expensive to build and to operate. This paper introduces a new design of mechanical press whose performances are programmable, including the trajectory and the velocity of the stroke, and yet, it is relatively inexpensive to build and to operate. The key idea of the new design is a 2-degree-of-freedom seven-bar linkage mechanism driven by a large constant speed motor and a small servomotor. First, the kinetics and kinematics of the design are presented including the feasibility conditions, mechanical advantage, as well as the torque and power distribution between the two motors. Next, a number of simulation results are given. The design (parameter) optimization is also carried out using Genetic Algorithm (GA). Based on computer simulation, it is shown that the new design is indeed very attractive.

Type synthesis for 4-DOF parallel press mechanism using GF set theory

Parallel mechanisms is used in the large capacity servo press to avoid the over-constraint of the traditional redundant actuation. Currently, the researches mainly focus on the performance analysis for some specific parallel press mechanisms. However, the type synthesis and evaluation of parallel press mechanisms is seldom studied, especially for the four degrees of freedom(DOF) press mechanisms. The type synthesis of 4-DOF parallel press mechanisms is carried out based on the generalized function(GF) set theory. Five design criteria of 4-DOF parallel press mechanisms are firstly proposed. The general procedure of type synthesis of parallel press mechanisms is obtained, which includes number synthesis, symmetrical synthesis of constraint GF sets, decomposition of motion GF sets and design of limbs. Nine combinations of constraint GF sets of 4-DOF parallel press mechanisms, ten combinations of GF sets of active limbs, and eleven combinations of GF sets of passive limbs are synthesized. Thirty-eight kinds of press mechanisms are presented and then different structures of kinematic limbs are designed. Finally, the geometrical constraint complexity(GCC), kinematic pair complexity(KPC), and type complexity(TC) are proposed to evaluate the press types and the optimal press type is achieved. The general methodologies of type synthesis and evaluation for parallel press mechanism are suggested.

Type synthesis of parallel mechanisms having the first class gf sets and one-dimensional rotation

A method is presented for the type synthesis of a class of parallel mechanisms having one-dimensional (1D) rotation based on the theory of Generalized Function sets (GF sets for short), which contain two classes. The type synthesis of parallel mechanisms having the first class GF sets and 1D rotation is investigated. The Law of one-dimensional rotation is given, which lays the theoretical foundation for the intersection operations of GF sets. Then the kinematic limbs with specific characteristics are designed according to the 2D and 3D axis movement theorems. Finally, several synthesized parallel mechanisms have been sketched to show the effectiveness of the proposed methodology.

Kinematic and dynamic analyses of the multi-actuated mechanical press with parallel topology

This article proposes a new type of multi-actuated mechanical press with parallel topology to develop high stamping capacity. Four active limbs actuated by servomotor deliver forces and motions to moving platform, and the passive limbs are driven by moving platform to push or pull the ram. This four-input-single-output system realizes multiple actuations without causing being over-constrained. Due to infinite number of solutions for the inverse kinematics, selection of actuation schemes for given ram trajectories is more crucial. Further, the principle of virtual work is used in the inverse dynamic problem. By choosing the pose variables of moving platform as generalized coordinates to describe the manipulator system, the linear form of dynamic models is derived. A typical deep-drawing process with nominal 25,000 kN capacity and 1200 mm stroke is simulated, and the required driving torques are computed. These performance analyses provide a basis to the design of the control law or the estimation of servomotor parameters for the mechanical press.

Snake Skeleton Graph: A New Method for Analyzing Signals That Contain Spatial Information

Many modern engineering systems use multiple sensors for monitoring, diagnosis and control. Some of these sensors contain not only time domain and frequency domain information, but also valuable spatial domain informationto which little attention has been paid. This paper presents a new method for capturing the spatial characteristics of the sensor signals. The basic idea is to model the spatial information of the signals using a Bezier surface. For example, given m one-dimensional force signals: X 1 (t),X 2 (t),...,X m (t), at each time instance t, a Bezier surface can be constructed, which describes the distribution of the force. Furthermore, lining up the surfaces at different time t 1 , t 2 ,..., t n , will show how the force changes as a function of time. Since the graph looks like a snake skeleton, the new method is called the snake skeleton graph. The paper first describes how the snake skeleton graph is constructed using a demonstration example: afoot walking on a plate. Then it presents an application for fault diagnosis in sheet metal stamping operation. Future research topics are also discussed.

On the Mobility of Single Loop N-Bar Linkage With One Prismatic Joint

Single loop N-bar linkages that contain one prismatic joint are common in engineering. This paper presents a systematical study on the mobility of this type of mechanism. It is found that this type of mechanisms can be divided into three categories: Class I, Class II and Class III. For each category, the slide reachable range is cut into different regions: Grashofian region, non-Grashofian region and change-point region. At each region, the rotation range of the revolute joint or rotatability of the linkage is able to determine based on Ting’s criteria. The characteristics charts are given to describe the rotatability condition. For active prismatic joint, the input revolute joint(s) is/are dependent in non-Grashofian region but independent in other regions. For passive prismatic joint, the revolvability of input revolute joints is dependent on the offset distance of the prismatic joint. Two special cases are illustrated with four and five bars. Examples are given to demonstrate the presented method able to cover all the cases of N-bar linkages with one or a set of adjoined prismatic joints and N-bar open-loop robotic mechanisms.Copyright

Innovative group-decoupling design of a segment erector based on G F set theory

The segment erector is a key part of the shield machines for tunnel engineering. The available segment erectors are all of serial configuration which is suffering from the problems of low rigidity and accumulative motion errors. The current research mainly focuses on improving assembly accuracy and control performance of serial segment erectors. An innovative design method is proposed featuring motion group-decoupling, based on which a new type of segment erector is developed and investigated. Firstly, the segment installation manipulation is analyzed and decomposed into three motion groups that are decoupled. Then the type synthesis for the 4-DOF motion group is performed based on the general function(GF) set theory and a new configuration of (1T⊕1R⊕1PS&3UPS) is attained according to the segment manipulation requirements. Consequently, the kinematic models are built and the reducibility and accuracy are analyzed. The dexterity is verified though numerical simulation and no singular points appear in the workspace. Finally, a positioning experiment is carried out by using the prototype developed in the lab that demonstrates a 13.1% improvement of positioning accuracy and the feasibility of the new segment erector. The presented group-decoupling design method is able to invent new type of hybrid segment erectors that avoid the accumulative motion error of erecting.

The Design of a Programmable Metal Forming Press and Its Ram Motion

Metal forming is one of the oldest production processes that can be traced back to the beginning of the Industry Revolution. Today, metal forming press is still one of the most commonly used manufacturing machineries. Every day, millions of parts are produced by metal forming ranging from battery caps to automotive body panels. Therefore, even a small improvement may add to significant corporative gain.

The new design of stabilised platform for target seekers using two-dof spherical linkage

A target seeker is an important portion of the guidance system for the flying vehicles to track fixed/flying objects. In the target seeker, the stabilised platform is fundamental as it provides pointing capability to maintain the apparatus mounted on it a desired time-invariant or time-variant pose. In this paper, a new design of the stabilised platform is investigated using a two-degree-of-freedom (dof) spherical linkage driven by two fixed motors. The configuration, forward and inverse kinematics, singularity as well as linearity are discussed. Then, the driving torques are modelled and investigated that leads to balance design. Furthermore, the balance design is detailed considering the motion of the flying base. Simulations illustrate the new design and a prototype is developed in the laboratory.

A novel method to model the effect of environmental constraint of geometry in the mechanism design

Few studies have considered the effect of environmental constraints throughout the entire design process of mechanical systems. Neglecting such effect might lead to misunderstanding the kinematic performance of the mechanical systems. In our work, an environment-based design concept was proposed by using passive limbs to model and analyze geometrical constraints in each step of the theoretical design process. Redesigning of a thrust system in a shield machine is taken as an example for better demonstration of this design approach. A new equivalent model of the thrust system was synthesized by using passive limbs to express environmental constraints of geometry based on the shield behavior. The uniform kinematic model was developed for the integrated equivalent mechanism of the thrust system. The effectiveness of the passive limbs in expressing environmental constraints was then evaluated by kinematical analysis. A singularity analysis was performed to assess the consistency between the equivalent model and a real thrust system. The reachable angular workspace was also analyzed to demonstrate the influence of the passive limbs as an example of environment-based parameter design. A motion simulation was performed to demonstrate the improvement of the forward kinematics by using the passive limbs to solve the singularity problem. A dexterity performance index based on the proposed model was conducted to demonstrate the kinematical property of the thrust system.