Jerk (Rate of Acceleration Change)
Compute the jerk, J = Δacceleration/Δtime, the rate of change of acceleration over time — the third derivative of position. High jerk causes jolts, vibration and wear; controlling it (jerk-limited or S-curve profiles) makes motion smooth, protecting mechanisms and improving the finish on CNC machines and elevators. Enter the acceleration change and the time interval.
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Jerk (variação da aceleração)
Depois da posição, velocidade e aceleração vem o jerk (arranque, ou solavanco): a taxa de variação da aceleração no tempo, J = Δa/Δt — a terceira derivada da posição. É o que você sente quando um carro 'engasga' ao trocar de marcha, ou quando um elevador parte e para bruscamente: não é a aceleração em si, mas a sua mudança súbita. Jerk alto causa vibração, ressonância, desgaste de engrenagens e correias, e marcas de trepidação em peças usinadas. Por isso os controladores modernos usam perfis com limitação de jerk (S-curve), que suavizam as transições — a aceleração sobe e desce gradualmente em vez de 'ligar' e 'desligar'. O conforto em elevadores, trens e montanhas-russas é, em boa parte, controle de jerk. Informe a variação de aceleração e o intervalo de tempo.
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Trapezoidal Profile Time
Compute the total time of a motion with a trapezoidal velocity profile, t = d/Vmax + Vmax/a, adding the cruise-velocity time to the acceleration and deceleration phases. It is the most common motion profile in motors and robots: accelerate to maximum speed, hold constant and decelerate. Enter the distance, the maximum velocity and the acceleration (assuming equal acceleration and deceleration).
Follower Max Jerk (SHM)
Calculate the maximum jerk of a simple-harmonic-motion cam follower, j_max = (π³·h·ω³) ÷ (2·β³), from the total lift h (mm), the cam angular velocity ω (rad/s) and the rise angle β (rad). Jerk is the RATE OF CHANGE of acceleration (the third time-derivative of displacement). Though less known than velocity and acceleration, jerk is decisive for the SMOOTHNESS and vibration of a cam mechanism: abrupt acceleration changes (high jerk) generate SHOCKS that excite the system's natural frequencies, causing vibration, noise, fatigue and wear — even if peak acceleration is within limits. In SHM, although acceleration is continuous inside the rise, it is DISCONTINUOUS at the ends, meaning INFINITE jerk there (the formula gives the interior jerk peak, but the end discontinuities are the real problem). It is precisely to eliminate these acceleration discontinuities (infinite jerk) that CYCLOIDAL motion and polynomial profiles were developed — they ensure finite, continuous jerk, the choice for high-speed, precision cams. Jerk grows with the CUBE of the rotation ω, becoming critical at high speeds. Considering jerk is the mark of advanced cam design. Enter the lift, the angular velocity and the rise angle.
Max Acceleration (Parabolic Cam)
Calculate the (constant) maximum acceleration of a parabolic-motion (constant-acceleration) cam follower, a_max = (4·h·ω²) ÷ β², from the total lift h (mm), the cam angular velocity ω (rad/s) and the rise angle β (rad). Parabolic, or constant-acceleration, motion is the law producing the LOWEST possible maximum acceleration for a given lift and time — so it minimizes peak inertia forces. It consists of two halves: in the first, the follower accelerates with CONSTANT acceleration (rising parabolic displacement); in the second, it decelerates with the same constant (negative) acceleration, stopping at the top. The name 'parabolic' comes from the displacement diagram, formed by two parabolas. The great advantage is the low maximum acceleration; the drawback is that acceleration JUMPS abruptly — from +a_max to −a_max at the middle, and from zero to ±a_max at the ends — generating infinite JERK there, causing shocks, noise and vibration. So in practice pure parabolic is little used at high speed (despite low peak acceleration), and cycloidal or modified profiles that smooth these transitions are preferred. Parabolic is didactic and useful when peak acceleration is the limiting factor and speeds are moderate. Enter the lift, the angular velocity and the rise angle.
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