Papers by Keyword: Jerk

Abstract: Gas metal arc welding process has the capability of producing high quality, all position welding, and is easily adaptable for automated welding applications. Repair welding of random cracks on existing assembly/structure through automatic welding would need real time crack/gap identification and weld path generation. In this work, an image processing-based system is presented for identifying the crack geometry. Graphical user interfaces are also developed to take necessary user inputs required at different stages for crack identification, predicting weld bead dimension, and weld path generation. Based on the identified crack geometry and predicted weld bead feature, linear and curved weld path planning methodology is proposed. The proposed modules are validated for a case study by successfully generating the desired weld paths. Different natures of velocity profiles are considered to appraise the role on motion behaviour and a suitable profile is selected for reducing the jerks at sharp corners/via points on the weld path and maintaining uniform bead geometry.

Abstract: The paper investigates the effects of mechanical wheel slide protection devices (WSPD) on the braking capacity for coaches equipped with disc or cast iron block brakes. Decelerations and jerks, that affect the passengers comfort, are also analyzed. An original simulation program, based on experimentally determined air pressure evolutions in brake cylinder is used for this purpose. Results of numerical simulations show that in the case of repeated actuations of mechanical WSPDs, disc brake vehicles are more affected in terms of braking capacity. Regarding jerks during braking actions, in both normal and low adhesion conditions, vehicles equipped with high power cast iron block brake with two pressure levels prove to be more affected.

Abstract: For the shaking table system, the 90^o phase shift frequency of the servo valve system is close to the oil column resonance frequency, the bandwidth under the influence of servo valve features was so narrow that it cannot meet requirements. Multi-variable control is presented in this paper by introducing the jerk feedback on the basis of the three-variable control. The theoretical derivation and the system simulation show that: the jerk feedback can reduce the oil column resonance frequency, and decrease the influence of the system performance caused by the servo valve characteristics.

Abstract: Exciting the mechanical resonance mode and vibration caused by non-smooth trajectories can cause some failure in the structure of the robot and its actuators. This work proposes a smooth trajectory planning for 3 degree of freedom (dof) 3-upu parallel manipulator. We have used optimization method to define the smooth trajectory for this robot. In this paper an objective function has been used which contain a term related to the total execution time and a term corresponding to the integral of squared jerk. Some constraints have been applied to the problem as the input of our system. Task space and joint space trajectory are then considered as the output. In this method optimization techniques such as genetic algorithm and fmincon (function of MatLab^TM ) have been investigated. Six via points have been considered and B-splines have been used to present kinematic quantities.

Abstract: In this paper, the usual feedrate control methods are introduced. The characters of them are analyzed. The shortcomings such as the discontinuity of acceleration and jerk in these methods will influence the accuracy of CNC. In order to overcome the weaknesses, a novel feedrate scheme based on fractional power polynomial is proposed. The constraint condition is discussed. The jerk-time curves, acceleration-time curves feedrate-time curves are contrasted. The simulation result shows that this feedrate scheme can fulfill the requirements of high-speed and high-accuracy through the interpolation process.

Abstract: In order to improve the stability of feed movement in high speed CNC system, the feedrate planning algorithm based on piece-wise polynomial function was proposed. The flexible transition of feedrate was realized through maintaining linear continuous jerk. The principle of the proposed algorithm was introduced and the method to generate smooth motion profile based on the proposed algorithm was presented. The proposed algorithm is simple and it can be applied in acceleration/deceleration before interpolation in high speed feed movement to improve the stability of it. The proposed algorithm was applied in multi-contour high speed processing and the result indicated that it could improve the stability of large-scale parts motion.

Abstract: In high speed machining, excessive vibration and shock growing out of acceleration and jerk should be suppressed. Therefore, based on before acceleration/deceleration with linear jerk, a new NURBS curve interpolation was proposed. Interpolation feed and acceleration were planned employing before acceleration/deceleration with linear jerk evolution. During real-time interpolation, the interpolation feed and acceleration were calculated with polynomial fitting method, and with the second-order Taylor expansion, the interpolation parameter was computed. A NURBS curve was interpolated with the proposed method and the one with S curve acceleration/deceleration as comparison. The results indicated the proposed method not only maintain high feed but also reduce the interpolation output acceleration and jerk significantly, and its output jerk evolves along with time linearly. The proposed method can be used to reduce the vibration and shock from the high speed moving parts and improve their smoothness.

Abstract: In order to improve the stability of feed movement in high speed CNC system, the feedrate planning algorithm based on piece-wise polynomial function was proposed. The flexible transition of feedrate was realized through maintaining linear continuous jerk. The principle of the proposed algorithm was introduced and the method to generate smooth motion profile based on the proposed algorithm was presented. The rapidity, stability and tracking accuracy of the feedrate planning algorithm to linearity, S curve and the proposed one were analyzed. The proposed algorithm is simple and it can be applied in acceleration/deceleration before interpolation in high speed feed movement to improve the stability of it. The proposed algorithm was applied in multi-contour high speed processing and the result indicated that it could improve the stability of large-scale parts motion.

Abstract: A new joint space trajectory planning method for the series robot is proposed. Comparing with the traditional path planning methods which can only guarantee the planned trajectory velocity or acceleration continuous, the proposed trajectory planning algorithm can also ensure the derivative of acceleration (Jerk) continuous within a limit threshold. At the end of this paper, the proposed path planning algorithm is validated of having a great performance on robot trajectory tracking.

Abstract: Control of the motion process of acceleration/deceleration (Acc/Dec) is one of key complicated problems in CNC system development. The excellent Acc/Dec control can improve the processing precision. The traditional Acc/Dec algorithms such as the linear and the exponential are not suitable for high speed motion because there would be flexible impacts existing in feed motion, especially that the jerk of the S-shape curve Acc/Dec is discontinuous. A new flexible Acc/Dec algorithm for high speed motion system based on the squared sine function is introduced. The modeling of the Acc/Dec algorithm with Trigonometric Function Squared Sine(TFSS) shape curve is constructed.In this algorithm, the sine curve in jerk, acceleration, velocity and displacement are all continuous. The simulation experiments result demonstrate that the Acc/Dec algorithm with TFSS shape curve is a new method of continuous Jerk for the design flexible Acc/Dec.