Cures for low-frequency resonance 
Numerous methods can be used: low pass filter, low-pass in combination with high-pass named bi-quadratic (a.k.a. biquad) filter (two poles and two zeros).  Another method is to use acceleration feedback.
A combination of biquad with acceleration feedback dramatically improves performance. The biquad lowers the settling time by a factor three and raises the bandwith by the same factor. While acceleration feedback maintains stability margin.
A Luenberger observer takes input from the motor current and the encoder, adds the two, and feeds the sum to a motor model. The model then produces observed position and compares this with actual position. The PID observer compensator drives out most error up to the observer bandwidth, which is usually between 200 and 500 Hz. One by-product of the observer is an acceleration signal, which represents acceleration much better than double-differentiating the position-feedback signal. The step response of the baseline system shows a settling time of about 60 msec with some overshoot and a system bandwidth of 23 Hz.

Alain Codourey - Dynamic Modeling of Parallel Robots for Computed-Torque Control Implementation

Control of parallel robot with modern theory has been restrained. Mainly since simple modelling of the dynamic behaviour is needed to enable real time calculations. In this work a simple dynamic model based on the virtual work principle is established. The method is applied to the DELTA parallel robot, leading to a very efficient model that has been implemented in a real-time computed-torque control algorithm.
1. Introduction
 Keeping the motors on the robot base is a requirement when direct drive is used; thus, parallel robots are well suitedto direct-drive actuation.
The advantages of direct-drive robots are well known (Asada and Youcef-Toumi 1987): simple mechanical structure, elimination of backlash, reduction of friction and noise, and higher rigidity. This concept requires greater effort and sophistication at the controller level because of the mechanical coupling and inertial variations that are directly felt on each motor axis.