Currently, the widely used point-to-point motion control commands in the industry only support trapezoidal, sin², quadratic, and quadratic (smooth) acceleration/deceleration curves. This fails to meet the requirements in some practical applications:
▶Long travel time: Back-and-forth movement from point A to point B typically involves reduced acceleration and deceleration to avoid excessive mechanical impact, thus increasing the travel cycle. ▶Servo overcurrent: Frequent high-speed back-and-forth movement can trigger servo overcurrent alarms, increasing the equipment's alarm failure rate.
▶High mechanical impact: In order to achieve production efficiency, it is necessary to increase the acceleration, which makes it impossible to avoid mechanical impact at high speeds when the point-to-point motion commands of the original platform are executed.
To meet the above requirements, LeadSys developed the ModConsVelMoveAbs function block, which integrates four different types of curves: AccTrap, VelTrap1, VelTrap4, and ModConsVel. It is a motion control algorithm developed based on the LeadSysStudio platform. It mainly realizes precise point-to-point motion control from point A to point B, supports single-command multi-mode switching, and meets the full range of fast, accurate, and stable requirements in industrial scenarios, from basic positioning to precision machining.
Leadshine Process Solutions
Absolute motion ModConsVelMoveAbs
This function block contains four types of trapezoidal functions:
1. AccTrap acceleration T-shape.
2. VelTrap1 speed T-shaped linear acceleration and deceleration.
3. VelTrap4 speed T-shaped quartic curve acceleration and deceleration.
4. ModConsVel deformation isovelocity curve.
Different modes can be selected via eMoveCureType, as shown in the curve below:
AccTrap acceleration T-shape
The acceleration curve exhibits a T-shaped distribution, with configurable parameters including dTa, total motion duration, and target displacement. The parameter dTa is used to adjust the acceleration and deceleration segments in the acceleration curve. These adjustment regions are represented by four completely symmetrical intervals on the curve, thus the effective value range of dTa is limited to [0, 0.25].
VelTrap1 speed T-shaped linear acceleration and deceleration
A T-shaped velocity curve is used, providing four adjustable parameters: dTa, dTb, total motion time, and target position. dTa is used to set the time proportion of the acceleration phase (value range [0, 0.5]), while dTb is used to set the time proportion of the deceleration phase (value range [0, 0.5]).
This T-shaped acceleration/deceleration pattern is the most commonly used ramp pattern in the CODESYS platform, and its characteristics are:
① There is a sudden change in acceleration at the velocity inflection point;
② It has high execution efficiency;
③ It can effectively reduce the maximum speed, acceleration and current requirements.
When cubic or quintic polynomial curves fail to meet efficiency requirements, it is recommended to try using VelTrap1 type curves for testing and verification.
VelTrap4 speed T-shaped quadratic curve acceleration and deceleration
It adopts a T-shaped velocity curve and supports the setting of four parameters: dTa, dTb, total motion time, and target position. Its operating characteristics are similar to the VelTrap1 curve, but the difference is that the system uses a fifth-order position function (corresponding to a fourth-order velocity function) during acceleration and deceleration. This design can significantly reduce torque impact, but it will correspondingly increase the maximum speed, acceleration, and current requirements.
ModConsVel deformation isotropic curve
The deformation is a uniform velocity curve, with configurable parameters including dTa, dTb, total motion time, and target position. Its features include:
① Segmented processing is adopted during the acceleration phase;
② A smooth transition between the acceleration and deceleration zones is achieved using a sine curve;
③ The dTb parameter controls the overall ratio of the acceleration/deceleration interval (value range 0-0.5);
④ The dTa parameter adjusts the range of acceleration variation within the acceleration interval (value range from 0 to dTb);
⑤ When dTb = 2dTa, its motion characteristics are very similar to the T-shaped quartic curve pattern;
This design ensures smooth motion while providing flexible parameter adjustment capabilities.
● Customer Value ●
Dynamic response optimization
It operates faster than the positioning commands built into the original platform. The shift time of a certain terminal client device has been reduced to 510ms, a 10% improvement over Codesys's secondary (smooth) absolute positioning of 530ms.
Energy efficiency improvement
The algorithm can plan different acceleration curves, thereby reducing operating current. For example, the current of a certain end-customer's equipment decreased from 125A to 90A, a reduction of 28%.
Small mechanical impact
By employing high-order or sinusoidal composite algorithms, continuous acceleration changes without abrupt changes are achieved, thereby reducing mechanical impact.
Flexible and versatile
By selecting the mode and adjusting the Ta and Tb values, different scenario requirements can be flexibly adapted.
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