Swift4の加速度センサ値の取得について

###前提・実現したいこと
textviewに配列に格納した加速度を時間ごとに見やすく表示させたい

###発生している問題・エラーメッセージ
コンパイルは通るのですがThread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional valueが出て動きません。多分self.~のところで何か起きてると思うのですが何がいけないのかわかりません

エラーメッセージ
```Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

###該当のソースコード
```swift4
import UIKit
import CoreMotion

class ViewController: UIViewController {
    let motionManager = CMMotionManager()
    var dataX:[Double] = []
    var dataY:[Double] = []
    var dataZ:[Double] = []
    
    @IBOutlet weak var accelX: UILabel!
    @IBOutlet weak var accelY: UILabel!
    @IBOutlet weak var accelZ: UILabel!
    @IBOutlet weak var TextView: UITextView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        if motionManager.isAccelerometerAvailable {
            motionManager.accelerometerUpdateInterval = 0.2
            
            motionManager.startAccelerometerUpdates(
                to: OperationQueue.current!,
                withHandler: {(accelData: CMAccelerometerData?, errorOC: Error?) in
                    self.outputAccelData(acceleration: accelData!.acceleration)
            })
            
        }
    }
    
    func outputAccelData(acceleration: CMAcceleration){
        accelX.text = String(format: "x = %.4f", acceleration.x)
        accelY.text = String(format: "y = %.4f", acceleration.y)
        accelZ.text = String(format: "z = %.4f", acceleration.z)
        
        dataX.append(acceleration.x)
        dataY.append(acceleration.y)
        dataZ.append(acceleration.z)
        
        TextView.text = String(format: "%.2f %.2f %.2f\n",dataX,dataY,dataZ)
        
        if ((acceleration.x >= 1.0)||(acceleration.x <= -1.0)) {
            accelX.textColor = UIColor.red }
        else if((acceleration.x <= 1.0)||(acceleration.x >= -1.0)) {
            accelX.textColor = UIColor.black }
        if((acceleration.y >= 1.0)||(acceleration.y <= -1.0)) {
            accelY.textColor = UIColor.red }
        else if((acceleration.y <= 1.0)||(acceleration.y >= -1.0)) {
            accelY.textColor = UIColor.black }
        if((acceleration.z >= 1.0)||(acceleration.z <= -1.0)) {
            accelZ.textColor = UIColor.red }
        else if((acceleration.z <= 1.0)||(acceleration.z >= -1.0)) {
            accelZ.textColor = UIColor.black }
        
    }
    
    func stopAccelerometer(){
        if (motionManager.isAccelerometerActive) {
            motionManager.stopAccelerometerUpdates()
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}