Is there a way to make the artificial grass blades stand up all the time?

There are couple of things you can do to keep the artificial grass blades standing up over time:

Make sure to have infills in the grass: most of initial installations will have infills, but as time goes by, some of the infills might get washed away, so adding more infills might become necessary.
More importantly, you should brush/broom up the blades as soon as you notice that they are laying down, do so during a warm sunny day will be more effective. Artificial grass has “memories” in them, you would not want the fibers to start “remembering” to be laid down. So brush or broom the fibers during a warm sunny day can definitely help to remove the memory and make your turf standing up longer. Please let us know if you have further questions by email or this online form: https://megagrass.com/pages/free-estimates