Is there a way to constraint one of the robot arm's joints while it moves?

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Description

Hi everyone,

I am currently using MoveIt's programming interface to control and send commands to move a Robot's (Fetch Robot) arm in simulation. I was wondering if there is a way to constraint one or more of the robot's arm joints while it is executing a Cartesian path. The robot is capable of moving to the desired locations, however, the configuration of the arm is not ideal (the elbow lowers significantly during movement). It would be beneficial to have the elbow stay at an the desired height. I would appreciate any tips on how to accomplish this. Gracias.

Your Environment

ROS Distro: Kinetic OS Version: Ubuntu 16.04