Belt-Cable Properties

General characteristics of the cord of a pulley system

Libraries:
Simscape / Multibody / Belts and Cables

Description

The Belt-Cable Properties block sets the attributes of a pulley cord, among them its geometry and color, as well as its alignment constraints. For the purpose of visualization, the cord is treated as a one-dimensional line with color and opacity. Circular arc segments straddle the pulleys and straight line segments bridge the distances between the arcs.

By default, the cord can enter and exit a drum—pulley or spool—at an angle to its center plane. This angle can vary during simulation—for example, due to translation of the drum on a prismatic joint. While the contact point is always in the center plane of the drum, the drum can move when mounted on a joint. Use this strategy to model, for example, the winding of a cord on a spool and the fleet angle of the same (denoted θ in the figure).

The cord can also be constrained to enter and exit a drum in the center plane of that drum. The assembly may still be three-dimensional, with different pulleys on different planes, but only as long as the contact angles are each zero. Set the Drum Belt-Cable Alignment block parameter to Monitored Planar to enforce this constraint. (Because the constraint is monitored, the simulation stops with an error if a contact angle should be other than zero.)

Other attributes are set automatically by modeling assumptions and calculations. Among the assumptions are those of a massless cord that is both inextensible and always taut. Length is determined at the moment of assembly and fixed thereafter. Its value is consistent with a cord that precisely spans the pulley system as arranged in its initial configuration.

That configuration depends on the starting positions of the various joints in a model. These are matched where feasible to the state targets specified in the joint blocks. It is possible to use those targets to set the length of the cord and to guide the placement of its ends—for example to apply an initial rotation to a spool or an initial translation to a load-bearing anchor.

The belt-cable port (P) identifies the cord characterized by this block. It matters little where in a belt-cable network the port connects. It is important, however, that each belt-cable network in a model contain one instance of this block. A belt-cable network is distinct from another if there is no belt-cable connection line between the two.

The visualization of the cord is by default on but it can be suppressed in the block. If it is on, you can click any point on a cord to highlight its entire length. Look in the tree view pane for the name of the Belt-Cable Properties block associated with the selected cord—the block name is identified there. Right-click the block name and select Go To Block if necessary to update the cord visualization properties.

Examples

Block and Tackle with Four Pulleys

Models a block and tackle with four pulleys. Torque is applied to a winch which acts through the pulley mechanism to lift a load. Blocks from the Simscape™ Multibody™ Belts and Cables library are used to model the block and tackle.

Open Model

Cable-Driven Cross Slide Table

Models an XY cross positioning table that uses a cable-driven mechanism. A single cable wraps around seven different pulleys and converts the rotational angle of the two input pulleys to the x-y position of the table.

Open Model

Cable Robot

Models a cable robot. The robot comprises 8 independent belt-cable circuits which control the 6 degrees-of-freedom of the mover. A ball is dropped from a fixed height down the center axis of the mechanism. The mover initially starts directly below the ball and the contact is modeled between the mover and the ball such that the ball bounces elastically when striking the mover. The objective of the mover is to perform increasingly complex maneuvers between successive bounces of the ball. The mover is motion actuated from which the necessary cable, pulley, and motor spool kinematics are computed.

Open Model

Pulley Mechanism Right Angle Drive

Models a pulley mechanism that takes a torque applied to a winch and transmits it to a pulley rotated at 90 degrees to that winch. This example uses blocks from the Simscape Multibody Belts and Cables library to model a pulley mechanism that is not all in a single plane.

Open Model

Cable Driven Space Manipulator

Models a cable driven space manipulator. The manipulator comprises of 2 links connected via a system of revolute joints. Each link consists of belt-cable circuits which drive the movements of the manipulator. It also consists of a spring-damper system which provides different stiffness requirements. A space application is shown in this example where the objective of the manipulators is to capture a small satellite. The manipulators start from folded states and then perform necessary maneuvers to extend and reach the desired position. The pulleys are motion actuated from which necessary belt-cable kinematics are computed.

Open Model

Tower Crane with Trolley and Hoist

Models a tower crane with a trolley and a hoist. The hoist can raise and lower a load, and the trolley moves the load towards and away from the tower. Blocks from the belts and cables library are used to model the pulleys that control lifting the load and moving the trolley.

Open Model

Elevator

Models an elevator system in Simscape™ Multibody™. The system is comprised of belt-cable pulley circuits which control the movement of the elevator and the door mechanism. The cable is approximated to be extensible by using high stiffness springs between the belt cable ends and the elevator. The motor pulley is motion actuated based on the necessary elevator kinematics computed from the Floor Number inputs. Effects of people entering and leaving the elevator are modeled using general variable mass blocks.

Open Model

Forklift

Models a forklift which uses the hydraulic and pulley mechanisms to perform the lift action. The tilting of masts is also controlled by hydraulic cylinders. The forklift comprises of 3 masts, namely main mast, top mast and fork mast. The main mast is connected to the chassis by revolute joints and its tilting is governed by the hydraulic tilt cylinders. The top mast slides over the main mast and its motion is governed by the hydraulic lift cylinders. The fork mast slides on the top mast and hangs through belt-cable circuits which drives the movement of the fork mast. A common warehouse application is shown in this example where the objective of the forklift is to grab a box, pass over a bump and place the box in the racks. Spatial Contact Force blocks are used at all contact locations to model the contact between the bodies. The contact between the ground surface and the wheels are modeled using infinite plane block and the contact between the forks and the box are modeled using the point blocks.

Open Model

Ports

Belt-Cable

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P — Belt-cable network attachment point
belt-cable

Attachment point for the belt-cable network whose properties this block aims to specify.

Parameters

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Drum Belt-Cable Alignment — Type of alignment allowed between the cord and the center plane of a drum
`Unrestricted` (default) | `Monitored Planar`

Type of alignment allowed between the cord and the center plane of a drum (whether pulley or spool). Select Unrestricted to enable the cord to enter and exit the drum center plane at an angle. The entry and exit angles can differ during simulation. Select Monitored Planar to require that the cord always enter and exit a drum in line with its center plane. If at any time the contact angle differs from zero, the simulation then stops with an error.

Type — Means by which to visualize the cord
`Pitch Line` (default) | `None`

Means by which to show the cord in a model visualization. The default setting corresponds to a pitch line that arcs around each pulley and spool at the pitch radii specified in their respective blocks. The line segments are circular in the ranges of contact between the cord and pulley or spool; they are straight in the distances between the arcs.

Visual Properties — Parameterizations for color and opacity
`Simple` (default) | `Advanced`

Parameterizations for specifying visual properties. Select Simple to specify Diffuse Color and Opacity. Select Advanced to specify more visual properties, such as Specular Color, Ambient Color, Emissive Color, and Shininess.

Dependencies

To enable this parameter, set Type to From Geometry or Marker.

Color — Color of light due to diffuse reflection
[0.5 0.5 0.5] (default) | 3-by-1 or 1-by-3 vector with values in the range of 0 to 1 | 4-by-1 or 1-by-4 vector with values in the range of 0 to 1

Color of the graphic under direct white light, specified as an [R G B] or [R G B A] vector on a 0–1 scale. An optional fourth element (A) specifies the color opacity on a scale of 0–1. Omitting the opacity element is equivalent to specifying a value of 1.