Sims has had an up-and-down season, culminating in a poor performance last Sunday against the Buffalo Bills when he was responsible for two of the six sacks the team allowed. He hadn't allowed a sack through Detroit's first four games.
According to ratings by Pro Football Focus, Sims has been the Lions' worst offensive lineman this season. Caldwell told the Free Press' Dave Birkett he hasn't considered making a change.
"'I wouldn't agree with you in that (he's struggled),' Caldwell said. 'Rob does a good job in there for us. No one up front's been perfect. There hasn't been anyone on the field that's been perfect."
"Like I said, I think he's doing a fine job in there for us and he'll continue to get better,' Caldwell said. 'Not perfect, but he'll continue to do it better.'"
The Lions selected center Travis Swanson in the third round of this year's NFL draft with the belief he'd eventually develop into a starter. He has yet to appear in a game this season.
Sims and center Dominic Raiola are slated to become free agents at the end of the season.
Sims, 30, was selected by the Seattle Seahawks in the fourth round of the 2006 NFL draft. He joined the Lions in 2010 and has started every game for the team since.
The Lions are 3-2 this season and tied for first place in the NFC North. They travel to Minnesota to play the Vikings this Sunday.
- Ben Estes