Modeling Mechanical Systems
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Modeling Mechanical Systems SimMechanics gives you a complete set of block libraries for modeling machine parts and
connecting them into a Simulink block diagram. 1. Modeling Machines How to create a mechanical model with SimMechanics and Simulink 2. Modeling Bodies and Grounds How to represent a machine's mechanical environment and the mass and geometric properties of bodies 3. Modeling Joint How to represent degrees of freedom as joints 4. Modeling Constraints and Drivers How to represent time-independent and time-dependent constraints on relative body motions 5. Modeling Actuators How to apply forces, motions, and initial conditions to machines 6. Modeling Force Elements How to represent internal forces within machines 7. Modeling Sensors How to measure motions and forces in machines and create feedback loops to model internal forces 8. Checking Model Validity Special restrictions and requirements for block diagram models with SimMechanics blocks
Modeling Machines Machine In a SimMechanics model, a machine is a complete, connected block diagram representing one mechanical system. It is topologically isolated from any other machine in your model and has at least one ground. In SimMechanics the term machine has two meanings. It refers to a physical system that includes at least one rigid body. SimMechanics provides a library of Simulink blocks that allow you to create Simulink models of machines. It also refers to a topologically distinct and separate block diagram representing one physical machine. A model can have one or more machines.
Comparison to Other Simulink Models A SimMechanics model differs significantly from other Simulink models in how it represents a machine. An ordinary Simulink model represents the mathematics of a machine's motion, i.e., the algebraic代数的 and differential微分的 equations that predict the machine's future state from its present state. The mathematical model enables Simulink to simulate the machine. By contrast, a SimMechanics model represents the physical structure of a machine, the geometric and kinematic relationships of its component bodies. SimMechanics converts this structural representation to an internal, equivalent mathematical model. This saves you the time and effort of developing the mathematical model yourself. Creating a SimMechanics Model You create a SimMechanics model in much the same way you create any other Simulink model. First, you open a Simulink model window. Then you drag instances of SimMechanics and other Simulink blocks from the Simulink block libraries into the window and draw lines to interconnect the block The SimMechanics block library provides the following blocks specifically for modeling machines: Machine Environment blocks set the mechanical environment for a machine. Exactly one Ground block in each machine must be connected to a Machine Environment block. See the Running Mechanical Models chapter. Body blocks represent a machine's components and the machine's immobile surroundings (ground). See Modeling Bodies and Grounds. Joint blocks represent the degrees of freedom of one body relative to another body or to a point on ground. See Modeling Joints. Constraint and Driver blocks restrict motions of or impose motions on bodies relative to one another. See Modeling Constraints and Drivers. Actuator blocks specify forces, motions, variable masses and inertias, or initial conditions applied to bodies, joints, and drivers. See Modeling Actuators. Force element blocks model interbody forces. See Modeling Force Elements. Sensor blocks measure the forces on and motions of bodies, joints, and drivers. See Modeling Sensors. You can use blocks from other Simulink libraries in SimMechanics models. For example, you can connect the output of SimMechanics Sensor blocks to Scope blocks from the Simulink Sinks library to display the forces and motions of your model's bodies and joints. Similarly, you can connect blocks from the Simulink Sources library to SimMechanics Driver blocks to specify relative motions of your machine's bodies. Connecting SimMechanics Blocks In general, you connect SimMechanics blocks in the same way you connect other Simulink
